Leukocyte-rich versus leukocyte-poor platelet-rich plasma for Osteoarthritis: A systematic review

Abstract

Introduction

Osteoarthritis is an increasingly prevalent condition with limited conservative treatments. Platelet-rich plasma (PRP) therapy has gained attention, but its efficacy may depend on the type used. In particular, leukocyte-rich (LR-PRP) and leukocyte-poor (LP-PRP) formulations may influence outcomes, yet direct comparisons are limited.

Methodology

a systematic literature search and analysis of clinical trials, through PubMed database, were conducted to evaluate the effect of leukocyte – rich and leukocyte – poor platelet rich plasma in the treatment of osteoarthritis.

Results

11 articles were analyzed individually, including both in vivo and in vitro studies, to examine the effect of leukocytes in PRP.

Conclusion

This review highlights that current evidence is insufficient to determine whether adding leukocytes to PRP provides a clinical benefit in the treatment of osteoarthritis. Overall, results generally show no significant differences between LR-PRP and LP-PRP, suggesting that both may be effective. Although leukocytes were initially thought to induce inflammation, there is no conclusive evidence that local reactions are directly caused by them. Given the limitations of existing studies, further research is required to clarify the role of leukocytes in PRP therapy.

1. Introduction

1.1. Osteoarthritis Background

1.1.1. Epidemiology

Osteoarthritis (OA) is the most common musculoskeletal condition and the leading cause of disability worldwide [1]. It is estimated that 580 million people suffer from some form of OA around the world [2]. Its distribution is heterogeneous; for example, the incidence of knee OA in North America ranges between 12 and 21%, while in South America it is between 2 and 4% [3]. Furthermore, this condition is more prevalent in women and has a higher incidence in individuals over 60 years old [4].

1.1.2. RISK factors

Understanding the risk factors that can contribute to the development of the disease is essential for designing effective prevention strategies and lowering its incidence.

The main risk factor is aging, understood as the progressive loss of tissue and organ function over time. It has been shown that joint space decreases with each decade [5]. Genetics also plays a significant role, with between 39 and 78% of OA cases potentially attributable to genetic factors [6]. Genome studies can help identify which genes are involved in the development of a specific disease; currently there are 90 OA risk loci identified [7]. Variations in joint shape also influence the development of OA, undertaking surgical procedures to restore a more anatomically joint structure [8].

On the other hand, the most important modifiable risk factor is obesity, defined as a body mass index (BMI) greater than 30 kg/m2. Obesity has been associated with OA in weight-bearing joints such as the hip and knee, while it has not been described for non-weight-bearing joints like the hand [9].

1.1.3. Physiopathology

OA is a multifactorial pathology caused by different biological mechanisms that contribute to joint degeneration. The most relevant ones, for the development of this article, will be identified below.

1.1.3.1. MITOCHONDRIAL dysfunction

Chondrocytes are cells that form cartilage. When mitochondrial dysfunction occurs, they eventually die. This sign appears before cartilage degradation [10]. A series of consequent changes occur in the mitochondria.

There is an increase in reactive oxygen species (ROS), that is, the accumulation of oxygen free radicals, which leads to oxidative stress. The cell has a defense mechanism against this scenario to remove excess radicals and maintain homeostasis. When there is an overproduction of ROS, this mechanism is inhibited [11]. Oxidative stress has been shown to be related to collagen degradation, suggesting that ROS are involved in the catabolism of articular cartilage [12].

Furthermore, metabolic respiration is reduced, which represents a stressful situation at the cell, so it releases inflammatory markers [13]. These markers are capable of inhibiting the activity of the electron transport chain, consequently decreasing ATP synthesis [14].

Mitochondria is the organelle responsible for regulating cellular calcium levels; a concentration much higher than normal can lead to chondrocyte apoptosis [15].

Mitochondrial membrane permeability also increases, leading to the release of cytochrome c into the cytoplasm and the entry of BAX, a gene that regulates apoptosis, into the mitochondrial matrix. Bcl-2, a biomarker responsible for protecting cells from apoptosis, is also found in the mitochondrial matrix. The entry of BAX consequently increases the BAX/Bcl-2 ratio [16], inducing chondrocyte apoptosis.

Finally, mitochondrial DNA mutations are thought to be caused by increased ROS in chondrocytes. The resulting mitochondrial DNA damage could result in respiratory chain dysfunction, thus increasing chondrocyte apoptosis [13].

1.1.3.2. Synovitis

It is believed that most patients with OA develop synovitis, leading to a state of chronic inflammation [17]. Proinflammatory mediators have been isolated in the synovial fluid, which release enzymes that degrade the extracellular matrix, resulting in cartilage loss [18]. However, other anti-inflammatory markers have also been identified [19]. In a healthy joint, this is regulated through autocrine-paracrine cell signaling, whereas in a joint affected by OA, there is an imbalance between these markers, shifting toward cellular destruction [20].

With the degradation of the extracellular matrix, fragments are released into the synovial cavity, stimulating the immune system, which in turn activates more inflammatory cells [21].

1.1.3.3. Joint REMODELING

Joint destruction leads to the formation of osteophytes, osseocartilaginous outgrowths that attempt to repair the degenerative damage gradually caused in the joint by excessive mechanical load [22]. It is believed that osteophytes redistribute mechanical forces to protect the articular cartilage [23].

Subchondral sclerosis is the result of excessive loading, which produces microfractures in the subchondral trabeculae. These fractures consolidate and eventually remodel the bone [24].

1.1.4. Intraarticular treatment

1.1.4.1. PLATELET-RICH plasma

PRP is composed of plasma with a platelet concentration significantly higher than normal [25]. Platelets contain a high amount of growth factors, which induce cell proliferation, revascularization, and the repair of damaged tissue [26]. The most important growth factors released include vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF), hepatocyte growth factor (HGF), fibroblast growth factor (FGF), epidermal growth factor (EGF), insulin-like growth factors 1 and 2 (IGF-1, IGF-2), matrix metalloproteinases 2 and 9 (MMP-2, MMP-9), and interleukin-8 (IL-8) [27].

Its therapeutic effect was observed in the 1970s, when it was used in the treatment of thrombocytopenia [28].

In the 1990s, its use was introduced into sports medicine and has progressively extended to various other medical disciplines [29].

1.1.4.2. Platelets

The precursor cells of platelets are megakaryocytes, which are found in the extracellular matrix of the bone marrow. Their concentration in the blood ranges between 150,000 and 400,000 per microliter. Platelets are responsible for the aggregation process, contributing to the body's homeostasis and preventing hemorrhage [30].

It is now also known that platelets contain a large number of growth factors and cytokines that influence angiogenesis, inflammation, cell proliferation, and stem cell migration [28].

1.1.4.3. Types of platelet-rich plasma

There are several types of PRP. The first and most widely used classification was developed by Dohan Ehrenfest and collaborators. It is based on analyzing the fibrin architecture and the presence of leukocytes in the sample [31] (Table 1) (see Table 2).

Table 1.

PRP types.

	FIBRIN	LEUKOCYTES
Pure platelet-rich plasma (P-PRP)	Low density	No
Leukocyte- and platelet-rich plasma (L-PRP)	Low density	Yes
Pure platelet-rich fibrin (P-PRF)	High density	No
Leukocyte- and platelet-rich fibrin (L-PRF)	High density	Yes

Table 1. PRP types [1]. Pure platelet-rich plasma (P-PRP), also known as leukocyte poor platelet rich plasma (LP-PRP), does not contain leukocytes and the fibrin is low density [2]. Leukocyte and platelet - rich plasma (L-PRP), also known as leukocyte rich platelet rich plasma (LR-PRP), contains leukocytes but a low density fibrin [3]. Pure platelet-rich fibrin (P-PRF), which contains a high density of fibrin but no leukocytes [4]. Leukocyte and platelet-rich fibrin (L-PRF), contain a high density of fibrin and leukocytes.

Table 2.

Summary of data from articles related to inflammatory mediators, including study design, reviewers responsible for data extraction, year, number of articles, participants, age, intervention, follow-up, and results. These data are intended for biological characterization and should be considered hypothesis-generating rather than evidence of clinical efficacy.

AUTHORS (YEAR)	STUDY DESIGN	REVIEWERS (DATA EXTRACTION)	NUMBER OF ARTICLES	PARTICIPANTS	AGE	INTERVENTION	FOLLOW-UP	RESULTS
Braun et al. (2014)	Controlled laboratory study	NA	NA	4	NA	LR – PRP LP – PRP PPP	NA	Cellular death: LR > LP. IL-4: LR = LP (anti-inflammatory). IL-6, IL-1β: similar but > in LR (pro-inflammatory). IL-10: LP > LR (anti-inflammatory). TNFα: LP > LR (pro-inflammatory). LR – PRP: induces a greater pro-inflammatory effect.
Assirelli et al. (2015)	Controlled laboratory study	NA	NA	7	27 – 38 years	LR – PRP LP – PRP PPP	NA	LR – PRP: Increase FGF-2, IL-1β, IL-8 Decrease TIMP-4, HGF (Pro-inflammatory markers increase, anti-catabolic markers decrease)
Mariani et al. (2016)	Non – randomized controlled study	NA	NA	36 (19)	58 ± 9 years	LR – PRP AH	12 months (0, 2, 6, 12)	LR – PRP do not modify pro-inflammatory cytokines systemic and local levels 1 week post treatment.
Jayaram et al. (2023)	Controlled laboratory study	NA	NA	12 (6,6)	59,16 ± 11,78 years	LR – PRP LP – PRP	NA	IL-1Ra increases in LR – PRP (anti-inflammatory). IL-1β + TNFα no significant (pro-inflammatory). MMP-9 increases in LR – PRP (pro-inflammatory). LR – PRP (with an increased in neutrophils) is anti-inflammatory compared to LP – PRP (with an increased in neutrophils)

1.1.4.4. Sample collection

The sample can be obtained using the conventional method with a centrifuge or through commercially available PRP preparation kits.

Standardized protocols for PRP preparation were lacking, but recently, in 2022, Muthu et al. [32] proposed a protocol (Fig. 1) based on a study involving 40 healthy volunteers. They examined different variables such as centrifugation time, relative centrifugal force and the required blood volume. In addition, the authors evaluated the platelet concentration, structural integrity, viability and regenerative potential of the final PRP product.

Fig. 1.

LP-PRP preparation. First, blood is drawn directly from the patient. The sample is then centrifuged at 100g for 15 min to separate the blood's cellular components. The plasma is collected in a new tube and subjected to a second centrifugation at 1600g for 20 min. As a result, the platelets precipitate, so the upper two-thirds consist of PPP, while the lower third is the plasma with the highest platelet concentration—known as PRP. Elaborated by the authors. Created with BioRender.com.

During the first centrifugation step, the authors observed that platelet yield was optimized at a centrifugal acceleration of 100g; beyond which their efficiency decreased. Centrifugation time was also found to be a significant factor, with optimal results achieved after 15 min. This initial spin effectively separates the cellular components of whole blood, resulting in plasma accumulating at the top of the collection tube. This plasma must then be carefully transferred to a sterile secondary tube.

The second centrifugation step is performed at 1600g, a force beyond which platelet viability again begins to decrease. Here, a centrifugation time of 20 min was determined to yield the highest-quality platelet concentrate. The result of this second spin is the stratification of the plasma into two fractions: approximately two-thirds platelet-poor plasma (PPP) and one-third PRP, which settles at the bottom of the tube.

To prepare LR-PRP, following the first centrifugation, the blood really separates into three distinct layers. The top layer consists of plasma; the middle layer—a thin interface containing leukocytes—is referred to as the buffy coat; and the bottom layer in which the red blood cells are contained. In this case the middle and bottom layer are taken to the second spin [33] (Fig. 2).

Fig. 2.

LR-PRP preparation. First, blood is drawn directly from the patient. The sample is then centrifuged at 100g for 15 min to separate the blood's cellular components. The plasma and the buffy coat are collected in a new tube and subjected to a second centrifugation at 1600g for 20 min. As a result, the platelets precipitate, so the upper two-thirds consist of PPP, while the lower third is the plasma with the highest platelet and leukocyte concentration—known LR-PRP. Elaborated by the authors. Created with BioRender.com.

1.1.4.5. Sample preservation

In the process of preparing PRP from a whole blood sample, the use of anticoagulants is necessary to prevent the sample from clotting and to avoid premature activation of the platelets. Not only is the anticoagulant important, but it is also essential to use an appropriate resuspension medium.

The most commonly used anticoagulants in PRP preparation are ethylenediaminetetraacetic acid (EDTA) and citrate, both of which act as calcium chelators, inhibiting the coagulation cascade [34].

Many experts recommend avoiding the use of EDTA, as it is such a strong anticoagulant that it is believed to damage the platelet membrane. However, the bibliography is contradictory. In the study by Carvalho et al. [34], EDTA was shown to provide greater platelet viability and a higher recovery rate after activation compared to citrate, although it resulted in a lower amount of vascular endothelial growth factor (VEGF). On the other hand, they demonstrated that the most effective resuspension medium was plasma, as it contains additional growth factors and cytokines.

Given the current widespread application of PRP across various medical specialties, and the diversity of PRP formulations obtainable through modifications in its composition, this study aims to investigate, through a systematic literature review, which type of PRP yields superior clinical outcomes. The analysis will focus on LP-PRP and LR-PRP.

2. Methods

2.1. Search Proccess

PubMed was used to conduct scientific literature review, operating through MEDLINE database, in which studies from 2014 to 2024 were reviewed. The following keywords were used: “knee osteoarthritis”, “platelet rich plasma” and “leukocytes”.

To refine the search, the Boolean operator “&” was used between the keywords.

The resulting studies were reviewed in duplicate by 2 authors (R.S.G, M.M.V). Reviewer disagreements were settled by a joint review of the eligible studies, followed by a consensus decision.

2.1.1. Inclusion and exclusion criteria

The inclusion criteria were [1]: bibliography published in the last 10 years, except for those that provide highly relevant information [2]. Adult population, not children [3]. Osteoarthritis in weight-bearing joints, primarily the knee.

The exclusion criteria were [1]: articles that used PRP in animals [2]. Articles in joints that are not considered weight-bearing.

2.1.2. RISK of BIAS

Risk of bias was assessed according to the revised Cochrane risk-of-bias tool for randomized trials (RoB 2), the Risk of Bias in Non-Randomized Studies – of Interventions (ROBINS-I) for non-randomized trials and AMSTAR 2 for previous systematic reviews.

3. Results

To carry out the bibliographic search, the MeSH (Medical Subject Headings) terms “platelet rich plasma,” “leukocytes,” and “knee osteoarthritis” were used. The Boolean operator AND (&) was used to combine these terms for the search.

This search yielded 25 results, given the small number of articles, no filters were applied. After an initial review of the titles, 11 articles were selected, and 14 were excluded for using other combined treatments, being conducted on mice, or addressing different musculoskeletal conditions.

The next screening was done through the abstracts, selecting 10 articles and discarding 1 due to the unavailability of the full text.

Finally, the remaining 10 articles were read and 3 were excluded. One due to low scientific quality (a pilot study) and a short follow-up period (6 weeks); another due to its complexity in terms of molecular biology, which was beyond the scope of this review; and a third for focusing mainly on other study variables, being the effect of L-PRP secondary.

Through a manual search, 4 articles were added because of their scientific relevance for the development of this review.

A total of 11 articles were ultimately selected for this literature review (Fig. 3).

Fig. 3.

Flowchart. Created in estech.shinyapps.io.

4. Discussion

Many studies have demonstrated the effectiveness and safety of intra-articular treatment with PRP; however, the main objective of this research is to determine which type of PRP—leukocyte-rich (LR-PRP) or leukocyte-poor (LP-PRP)—is more suitable for treating osteoarthritis (OA).

Although the scientific interest in PRP has increased over the past decade, the available literature directly comparing LR-PRP and LP-PRP remains limited and heterogeneous. The included studies differ substantially in design—ranging from randomized controlled trials (RCTs) [35,36], controlled laboratory studies [[37], [38], [39]], and prospective non-randomized comparative studies [40,41], to systematic reviews and meta-analyses [42,43]—as well as in sample size, follow-up duration, outcome selection, and PRP preparation protocols. This variability affects the consistency of the findings and limits the overall strength of evidence. While RCTs represent higher-level evidence, they remain few, and laboratory studies, though mechanistically informative, do not directly translate to clinical outcomes. These factors must be considered when interpreting the conclusions of the present work.

4.1. Effect of leukocytes

The role of leukocyte concentration in PRP remains one of the most debated topics in the field of orthobiologics. Laboratory and mechanistic studies have historically suggested that leukocytes may promote pro-inflammatory pathways through the release of catabolic cytokines and matrix-degrading enzymes [37].

Some preclinical investigations have also reported sustained upregulation of inflammatory mediators in leukocyte-rich preparations, reinforcing the hypothesis of a potential pro-inflammatory effect. However, more recent clinical and translational studies challenge this assumption. Jayaram et al. demonstrated that LR-PRP exhibited predominantly anti-inflammatory activity compared with LP-PRP in patients with mild to moderate knee OA [38]. Similarly, Mariani et al. reported that LR-PRP did not increase intra-articular pro-inflammatory cytokines following injection [39], suggesting that the presence of leukocytes may not universally trigger the inflammatory cascade previously hypothesized.

Biologically, discrepancies between LR-PRP and LP-PRP effects may relate to the balance and functional diversity of leukocyte subpopulations within the preparation. Neutrophils can contribute to acute inflammatory responses through the rapid release of proteases and reactive oxygen species, whereas monocytes/macrophages may support tissue repair and anti-inflammatory signaling. When platelet concentrations are equalized between formulations, LR-PRP has even been shown in laboratory settings to contain higher levels of anti-inflammatory cytokines such as IL-1Ra and IL-4, suggesting that the net biological effect depends on the combined cytokine profile of platelets and leukocytes rather than leukocyte presence alone. This mechanistic complexity offers a plausible explanation for the variability observed across studies.

Clinical evidence offers additional clarification. High-quality RCTs by Di Martino et al. [35] and Romandini et al. [36] observed no significant differences between LR-PRP and LP-PRP in terms of pain reduction or functional improvement, suggesting that leukocyte concentration may not meaningfully influence short- or mid-term clinical efficacy. This finding is consistent with the systematic review and meta-analysis by Kim et al., which concluded that adverse reactions were slightly more frequent in LR-PRP but that both formulations produced comparable clinical outcomes [43]. Additionally, the network meta-analysis by Abbas et al. observed no superiority of one formulation over the other regarding efficacy [39].

Overall, current evidence indicates that concerns regarding leukocyte-induced inflammation are not consistently supported. Mechanistic insights into cytokine profiles and leukocyte composition When platelet concentrations are equalized between formulations, LR-PRP has even been shown in laboratory settings to contain higher levels of anti-inflammatory cytokines such as IL-1Ra and IL-4, suggesting that the net biological effect depends on the combined cytokine profile of platelets and leukocytes rather than leukocyte presence alone. This mechanistic complexity offers a plausible explanation for the variability observed across studies.

4.2. Outcome measurement

Outcome measures across studies also show substantial heterogeneity, affecting the interpretability and comparability of results. Most clinical trials use validated scales such as the VAS, WOMAC, IKDC, or KOOS, which are widely recommended for assessing pain, function, and quality of life in knee OA [[44], [45], [46]]. However, the timing of outcome assessment varies considerably, ranging from a few months to over one year, complicating the identification of consistent temporal trends.

Some studies focus exclusively on clinical endpoints [35,36], whereas others include synovial fluid biomarkers [38,39] or use imaging-based assessments [40,41]. While biomarker analyses provide valuable insight into the biological response to PRP, the relationship between molecular changes and patient-reported outcomes remains unclear. Similarly, controlled laboratory studies, such as those by Braun et al. [37] and Assirelli et al. [47], offer mechanistic information but cannot be directly extrapolated to clinical efficacy.

A major source of variability across outcome measurements arises from the absence of a standardized PRP preparation protocol. Differences in centrifugation steps, force, duration, and inclusion or exclusion of the buffy coat can substantially modify platelet and leukocyte concentrations [31,33,40]. Even within a single study, inconsistencies in yield have been reported [33]. Since platelet-derived growth factors such as VEGF, PDGF, and IGF-1 are central to PRP's therapeutic mechanisms [27,28,48], such discrepancies limit the ability to draw definitive conclusions across studies. Although LP-PRP may reduce the likelihood of transient local reactions [43], clinical outcomes remain comparable between formulations [[35], [36], [42]] (Table 3).

Table 3.

Summary of clinical trials and comparative studies, including data from the articles involved in outcome measurements between groups (study design, reviewers responsible for data extraction, year, number of articles, participants, age, intervention, follow-up, and results). This higher-level evidence constitutes the primary basis for clinical decision-making and for evaluating treatment efficacy in the management of osteoarthritis.

AUTHORS (YEAR)	STUDY DESIGN	REVIEWERS (DATA EXTRACTION)	NUMBER OF ARTICLES	PARTICIPANTS	AGE	INTERVENTION	FOLLOW-UP	RESULTS
Filardo et al. (2012)	Non – randomized controlled study	NA	NA	144	NA	LR – PRP LP – PRP	12 months (0, 2, 6, 12)	LR – PRP and LP – PRP: IKDC 0 → 2. It stays the same. EQ-VAS 0 → 2 → 6 → 12. Tegner 0 → 2 → 6. It stays the same. More adverse reactions in LR – PRP.
Riboh et al. (2015)	Meta-Analysis	Reviewed in duplicate by 2 authors	9	1055	NA	LR – PRP LP – PRP AH Placebo	NA	IKDC no significant. WOMAC better results in LP -PRP. Local adverse reactions no significant.
Belk et al. (2020)	Meta-Analysis	Performed independently and then reviewed by a second author	18	811	57,6 years	LR – PRP [8] LP – PRP [7] AH	11,1 months	WOMAC and VAS no significant. Subjective IKDC, greater improved in LP – PRP.
Kim et al. (2021)	Systematic Review	Reviewed in duplicate by 2 authors	32	NA	NA	LR – PRP LP – PRP	12 months (0, 2, 6, 12)	WOMAC, IKDC y VAS no significant. More adverse reactions in LR – PRP.
Abbas et al. (2022)	Network Meta-Analysis	Reviewed by 2 authors with conflicts resolved by a third author	23	2260	NA	LR – PRP LP – PRP PPP	9,9 months	WOMAC greater improvement in LP – PRP. WOMAC pain greater improvement in LP – PRP at 6th month. IKDC, VAS, local adverse reactions no significant.
Di Martino et al. (2022)	Randomized Controlled Trial	NA	NA	192	18-80 years	LR – PRP LP – PRP	12 months (0, 2, 6, 12)	IKDC, specific question, adverse reactions and treatment failure no significant. EQ-VAS improves significantly in both groups.
Romandini et al. (2024)	Randomized Controlled Trial	NA	NA	132	NA	LR – PRP LP – PRP	12 months (0, 2, 6, 12)	Adverse reactions, treatment failure, final IKDC and specific question no significant. EQ-VAS improves until 6th month and then worsen, significant for LR – PRP IKDC 0 → 2, better in LR – PRP. At 6th month, active and passive knee ROM is better in LP – PRP. At 12th month quadriceps circumference is better in LR -PRP.

This heterogeneity in methodologies complicates the identification of consistent temporal trends and hinders robust cross-study comparison. A unified approach to outcome measurement—integrating validated clinical scales with well-defined follow-up intervals and, when appropriate, complementary biomarker or imaging metrics—would substantially improve the interpretability of PRP research. Standardized reporting of preparation protocols and cellular composition remains essential for comparing efficacy across studies and for determining whether biological differences between LR-PRP and LP-PRP translate into clinically meaningful outcomes.

4.3. Summary and interpretion of evidence

Considering the variability in study design, participant characteristics, PRP formulations and outcome measures, the overall strength of evidence supporting a differential clinical effect of LR-PRP and LP-PRP remains limited.

To ensure a rigorous interpretation of the findings for clinical practice, it is essential to distinguish between the different levels of evidence presented in this review. The mechanistic and in vitro studies (e.g., those examining leukocyte-mediated catabolic pathways and cytokine release) must be interpreted strictly as hypothesis-generating data. While these studies suggest that high leukocyte concentrations could theoretically induce a more robust inflammatory response in the joint environment [37], these biological observations do not directly equate to clinical outcomes.

Conversely, clinical decision-making and conclusions regarding treatment efficacy must rely on higher-level evidence, such as the randomized controlled trials (RCTs) and meta-analyses included in this review. Recent high-quality evidence from RCTs (Q1/Q2 journals) indicates that despite the theoretical concerns raised by in vitro models, there are no statistically significant differences in pain reduction or functional improvement between leukocyte-rich (LR-PRP) and leukocyte-poor (LP-PRP) formulations [35,48]. Therefore, while mechanistic data provide valuable insights into the biological behavior of PRP, clinical recommendations should be primarily guided by the functional and symptomatic outcomes derived from robust clinical comparative studies [36].

In line with this, high-level evidence from RCTs [35,36] consistently report no clinically meaningful differences between formulations. Systematic reviews and meta-analyses [42,43] reinforce this pattern, synthesizing data from broader samples and similarly concluding that leukocyte concentration does not appear to alter overall clinical effectiveness. Laboratory studies provide mechanistic insights, particularly regarding cytokine profiles and the balance of neutrophils and macrophages, but these findings do not directly translate into consistent clinical differences. Thus, while LP-PRP may reduce the incidence of mild post-injection inflammatory reactions in some patients [43], the current evidence does not support a clinically significant advantage of one formulation over the other in terms of pain relief or functional improvement. The totality of available evidence therefore suggests that the presence or absence of leukocytes alone does not determine PRP efficacy in OA. Instead, the interplay between platelet-derived growth factors, leukocyte subtypes, and the broader cytokine environment likely influences biological behavior, though current clinical data do not yet clarify the relative importance of these components.

The implications for clinical practice and research are considerable. Establishing standardized PRP preparation protocols—including explicit reporting of centrifugation parameters, platelet and leukocyte counts, and inclusion or exclusion of the buffy coat—is essential for meaningful comparison across studies. Without such standardization, the heterogeneity in final PRP products will continue to obscure the true effect of leukocyte concentration on therapeutic outcomes. Moreover, most available studies evaluate short-to mid-term results (<12 months), leaving open the question of whether structural or longer-term functional differences might emerge over time. Future research should therefore incorporate harmonized methodologies and extended follow-up periods to determine whether subtle biological differences between LR-PRP and LP-PRP have implications for long-term joint preservation and overall clinical benefit.

5. Limitations

The main limitation of this work is the lack of scientific studies directly comparing the application of LR-PRP and LP-PRP, which restricts the strength of the conclusions that can be drawn. This scarcity of comparative evidence necessitated the inclusion of studies with heterogeneous methodologies and, in several cases, relatively small sample sizes. Although these studies provide valuable insights, reduced statistical power may hinder the detection of subtle differences between formulations and may limit the generalizability of the reported findings.

It is important to highlight that one of the most significant limitations is the absence of a standardized PRP preparation protocol. Each study uses a different method, resulting in varying platelet concentrations—even within the same study across groups. Addressing this issue is crucial in order to establish a protocol and truly study the effect of leukocyte presence at a consistent platelet concentration.

Additionally, the diversity of outcome measures and follow-up durations across studies introduces further challenges. The use of different clinical scales, the inconsistent incorporation of biomarkers and variable reporting detail limit the ability to identify consistent trends and compare results across studies. Finally, incomplete reporting in several articles—particularly regarding preparation parameters, cellular content, or adverse events—may introduce bias and reduce the interpretability of the aggregated evidence.

6. Conclusion

Based on the findings of this review, it can be concluded that the presence of leukocytes in PRP preparations for the treatment of OA has not been sufficiently investigated to determine whether it is beneficial or detrimental. Despite this, it can be stated that the clinical outcomes observed in groups treated with LR-PRP and LP-PRP are quite similar, generally showing no statistically significant differences. This indicates that, according to current evidence, neither formulation demonstrates clear clinical superiority.

While some studies suggest that LP-PRP may be associated with fewer local inflammatory reactions, this potential advantage does not translate into consistent differences in clinical efficacy.

Although, it was initially assumed that intra-articular application of LR-PRP could trigger an inflammatory cascade due to the presence of leukocytes in the preparation, it is not yet certain that local reactions are caused by their concentration.

Given the methodological heterogeneity and limited number of high-quality comparative studies, further research using standardized PRP preparation protocols is required to clarify the true role of leukocytes and to optimize PRP formulations for clinical use.

Additional information

No additional information is available for this paper.

Author contributions

Conceptualization, RSG and MMV.; Methodology, RSG and IOS.; Software, MMV and RSL; Validation IZG.; Formal Analysis, PSW.; Investigation, RSG, AMA, RSL, MMV; Data Curation, AGC and IOS; Writing-Original Draft and Preparation RSG, IOS, IGZ, PSW; Writing-Review & Editing, RSG, MMV, IOS, AMA, IZG, PSW, RSL and AGC; Visualization, MMV; Supervision, IZG.; Project Administration, MMV and RSL; Funding Acquisition, anyone. Final approval of the version: all.

TABLES RISK OF BIAS.

ROBINS – I.

Study (Author, Year)	Randomization process	Deviations from intended interventions	Missing outcome data	Measurement of the outcome	Selection of the reported result	Overall risk of bias
Braun et al., 2014	High	Low	Low	Some concerns	Some concerns
Assirelli et al., 2015	High	Low	Low	Some concerns	Some concerns
Mariani et al., 2016	High	Low	Low	Some concerns	Some concerns
Jayaram et al., 2023	High	Low	Low	Low	Some concerns
Filardo et al., 2012	High	Low	Low	Some concerns	Some concerns

RoB 2.0.

Study (Author, Year)	Randomization process	Deviations from intended interventions	Missing outcome data	Measurement of the outcome	Selection of the reported result	Overall risk of bias
Di Martino et al., 2022	Low	Low	Low	Low	Low	Low
Romandini et al., 2024	Low	Low	Low	Low	Low	Low

AMSTAR 2 – RIBOH et al., 2016.

Item	Domain	Yes/Partial Yes/No	Your justification (brief, in English)
1	Did the research questions and inclusion criteria for the review include the PICO components?	Yes	Clear PICO: knee OA; interventions = LR-PRP, LP-PRP, or control; outcomes = pain/function; included RCTs and comparative studies.
2	Was a protocol registered before the review was conducted and deviations justified?	No	No protocol registration (e.g., PROSPERO) or a priori methodological documentation was reported.
3	Did the review authors explain their selection of the study designs for inclusion in the review?	Yes	They explicitly included RCTs and prospective comparative studies to compare PRP formulations.
4	Did the review authors use a comprehensive literature search strategy?	Yes	Multiple databases (MEDLINE, EMBASE, Cochrane Central) were searched with a clear strategy.
5	Did the review perform study selection in duplicate?	Yes	Two reviewers independently screened studies, resolving disagreements by consensus.
6	Did the review perform data extraction in duplicate?	Yes	Data extraction was performed independently by two reviewers.
7	Did the review authors provide a list of excluded studies and justify exclusions?	No	The PRISMA diagram was present, but no detailed list of excluded studies or reasons was provided.
8	Did they describe included studies in adequate detail?	Yes	Included studies were described with design, PRP characteristics, injections, outcomes, and follow-up.
9	Did the review authors use a satisfactory technique for assessing risk of bias in individual studies?	Partial Yes	They assessed quality using the modified Coleman Methodology Score—helpful but not equivalent to a domain-based risk-of-bias tool (Cochrane/ROBINS-I).
10	Did they report sources of funding for included studies?	No	Funding of included primary studies was not systematically reported.
11	If meta-analysis was performed, did they use appropriate statistical methods?	Yes	Appropriate Bayesian network meta-analysis methods were used, including SUCRA and model convergence checks.
12	Did they assess the potential impact of risk of bias on the meta-analysis?	Partial Yes	Study quality was mentioned, but no sensitivity analyses based on RoB were conducted.
13	Did they account for risk of bias when interpreting/discussing the review results?	Partial Yes	Limitations related to variability in study methodology were acknowledged, but RoB was not deeply integrated into interpretation.
14	Did they explain heterogeneity appropriately?	Yes	Heterogeneity and inconsistency were addressed using network methods and discussed appropriately.
15	Did they investigate and discuss publication bias?	No	Publication bias was not assessed.
16	Did they report their own conflicts of interest, including funding?	Yes	Authors declared conflicts of interest and funding as required by the journal.
—	Overall confidence in the results of the review (High/Moderate/Low/Critically low)	Moderate	Strengths: good search, duplicate processes, strong statistical methods. Weaknesses: no protocol, no excluded-study list, limited RoB methods, no publication bias assessment.

AMSTAR 2 – BELK et al., 2020.

Item	Domain	Yes/Partial Yes/No	Your justification
1	Did the research questions and inclusion criteria for the review include the PICO components?	Yes	Population defined, intervention, comparator and outcomes.
2	Did the review have an explicit statement that the methods were established prior to the conduct of the review and did the report justify any significant deviations from the protocol?	No	Not registered protocol found.
3	Did the review authors explain their selection of the study designs for inclusion in the review?	Yes	Only randomized trials were included.
4	Did the review authors use a comprehensive literature search strategy?	Yes	Multiple major databases were searched.
5	Did the review perform study selection in duplicate?	Yes	Two reviewers screened studies independently. Disagreements resolved by consensus.
6	Did the review perform data extraction in duplicate?	Yes	Two reviewers independently extracted data, reducing error and bias
7	Did the review authors provide a list of excluded studies and justify the exclusions?	No	Although a PRISMA flow diagram was included, a detailed list of excluded studies with reasons was not provided.
8	Did they describe included studies in adequate detail?	Yes	Tables describe sample size, interventions, PRP methods, outcomes and follow-up.
9	Did the review authors use a satisfactory technique for assessing the risk of bias (RoB) in individual studies included in the review?	Partial yes	Used the Jadad scale, less comprenhensive than Cochrane RoB tools.
10	Did they report sources of funding for included studies?	No	Funding sources of RCTs were not systematically reported.
11	If meta-analysis was performed, did the review authors use appropriate methods for statistical combination of results?	Yes	Used random-effects models, effect sizes, and I2 for heterogeneity.
12	Did the review authors assess the potential impact of risk of bias on the meta-analysis?	No	No sensitivity analyses or adjustments for study quality.
13	Did the review authors account for RoB in individual studies when interpreting/discussing the results of the review?	Partial yes	Mentioned quality variation but did not deeply integrate RoB into interpretation.
14	Did the review authors explain heterogeneity appropriately?	Yes	Heterogeneity quantified with I2 and discussed as related to PRP preparation differences.
15	Did the review authors investigate the presence and likely impact of publication bias?	Partial yes	Mentioned conceptually but no funnel plot or statistical tests performed.
16	Did the review authors report any potential sources of conflict of interest, including any funding they received for conducting the review?	Yes	Authors disclosed conflicts of interest and funding per journal guidelines.
	Overall confidence in the results of the review (High/Moderate/Low/Critically low)	Moderate	Multiple strengths but lacks protocol registration, excluded studies list, detailed RoB handling, and full publication bias assessment.

AMSTAR 2 - KIM ET AL.

Item	Domain	Yes/Partial Yes/No	Your justification
1	Did the research questions and inclusion criteria for the review include the PICO components?	Yes	The review clearly defines Population, Intervention, Comparator and Outcomes.
2	Was a protocol registered before the review was conducted and deviations justified?	No	No protocol registration was reported.
3	Did the review authors explain their selection of the study designs for inclusion in the review?	Yes	They specifically included RCTs and prospective comparative studies to evaluate PRP formulations' safety and outcomes.
4	Did the review authors use a comprehensive literature search strategy?	Yes	Multiple databases were searched with full search terms and a clear time frame.
5	Did the review perform study selection in duplicate?	Yes	Two reviewers performed study screening independently, with a consensus process to resolve disagreements.
6	Did the review perform data extraction in duplicate?	Yes	Data extraction was performed independently by two reviewers, reducing error and bias.
7	Did the review authors provide a list of excluded studies and justify exclusions?	No	A PRISMA flow diagram was included, but no detailed list of excluded studies with reasons was provided.
8	Did they describe included studies in adequate detail?	Yes	The authors reported study design, patient characteristics, PRP type, preparation techniques, injection protocols, and measured outcomes.
9	Did the review authors use a satisfactory technique for assessing risk of bias in individual studies?	Partial Yes	They assessed RoB using the Cochrane tool for RCTs and ROBINS-I for non-randomized studies, but reporting detail was limited.
10	Did they report sources of funding for included studies?	No	Funding was not reported.
11	If meta-analysis was performed, did they use appropriate statistical methods?	Yes	Proper statistical models were used (random-effects), along with heterogeneity assessment (I2).
12	Did they assess the potential impact of risk of bias on the meta-analysis?	Partial Yes	They discussed RoB qualitatively but did not perform sensitivity analyses to evaluate its impact on pooled estimates.
13	Did they account for risk of bias when interpreting/discussing the review results?	Partial Yes	Results were interpreted with some mention of study quality, but integration of RoB into conclusions was limited.
14	Did they explain heterogeneity appropriately?	Yes	Heterogeneity was quantified and discussed, especially regarding differences in PRP preparation methods.
15	Did they investigate and discuss publication bias?	Partial Yes	A funnel-plot–based assessment was attempted but limited by the number of included studies; discussion was brief.
16	Did they report their own conflicts of interest, including funding?	Yes	Authors provided disclosure statements and funding information according to journal requirements.
—	Overall confidence in the results of the review (High/Moderate/Low/Critically low)	Moderate	Key strengths include comprehensive search, duplicate processes, and appropriate meta-analysis. Main weaknesses: no protocol, no excluded-study list, incomplete RoB handling, and partial publication bias assessment.

AMSTAR 2 – ABBAS ET AL.

Item	Domain	Yes/Partial Yes/No	Your justification
1	Did the research questions and inclusion criteria for the review include the PICO components?	Yes	Clear PICO: knee OA patients; interventions = PRP formulations (LR, LP, or unspecified); comparators = other PRP types or control; outcomes = pain/function.
2	Was a protocol registered before the review was conducted and deviations justified?	No	No protocol registration was reported.
3	Did the review authors explain their selection of the study designs for inclusion in the review?	Yes	The authors specified inclusion of RCTs and comparative studies appropriate for network meta-analysis.
4	Did the review authors use a comprehensive literature search strategy?	Yes	Multiple databases were searched with clear search terms and time limits.
5	Did the review perform study selection in duplicate?	Yes	Two reviewers independently screened titles/abstracts and full texts, with a consensus process.
6	Did the review perform data extraction in duplicate?	Yes	Data extraction was performed by at least two reviewers independently, minimizing bias.
7	Did the review authors provide a list of excluded studies and justify exclusions?	No	A PRISMA flowchart was included, but excluded studies with reasons were not listed.
8	Did they describe included studies in adequate detail?	Yes	Study characteristics, PRP preparation details, doses, follow-up times, and outcomes were reported in detail.
9	Did the review authors use a satisfactory technique for assessing risk of bias in individual studies?	Partial Yes	Risk of bias was assessed using a combination of established tools, but reporting was limited and some domains lacked detail.
10	Did they report sources of funding for included studies?	No	Funding information of the included primary studies was not systematically documented.
11	If meta-analysis was performed, did they use appropriate statistical methods?	Yes	A network meta-analysis was performed using appropriate models, consistency testing, and heterogeneity assessment.
12	Did they assess the potential impact of risk of bias on the meta-analysis?	Partial Yes	RoB was acknowledged, but no detailed sensitivity analyses were performed to evaluate its influence on network results.
13	Did they account for risk of bias when interpreting/discussing the review results?	Partial Yes	RoB was mentioned in interpretation, but integration into final conclusions was limited.
14	Did they explain heterogeneity appropriately?	Yes	Heterogeneity and inconsistency were addressed through standard NMA diagnostics and discussed.
15	Did they investigate and discuss publication bi	Partial yes	Publication bias was discussed, but statistical testing or funnel plots were limited due to study numbers.
16	Did they report their own conflicts of interest, including funding?	Yes	The authors disclosed conflict-of-interest statements and funding in accordance with journal policies.
	Overall confidence in the results of the review (High/Moderate/Low/Critically low)	Moderate	Strong search and analysis methods, but weakened by lack of protocol, no excluded-study list, incomplete RoB assessment, and partial publication-bias evaluation

Funding Statement

The present research did not receive any specific grant from funding agencies in the public, commercial or not-for-profit sectors.

Declaration of competing interest

My signature indicates I have no commercial associations that might pose a conflict of interest in connection with the submitted article, except as disclosed on a separate attachment.

Data availability

No data was used for the research described in the article.