Association of HbA1c levels with neutrophil-to-lymphocyte ratio, monocyte-to-lymphocyte ratio, and platelet-to-lymphocyte ratio in patients with diabetes mellitus: a case–control study

Abstract

Background

The prevalence of diabetes mellitus in the general population has been increasing in recent years, and diabetes-related complications contribute substantially to morbidity, mortality, and healthcare system burden. This study aimed to evaluate the relationship between glycated hemoglobin (HbA1c) levels and inflammatory markers, including the neutrophil-to-lymphocyte ratio (NLR), monocyte-to-lymphocyte ratio (MLR), and platelet-to-lymphocyte ratio (PLR), in individuals diagnosed with type 2 diabetes mellitus (T2DM).

Methods

This retrospective case–control with longitudinal follow-up study included 138 patients with T2DM followed at the Internal Medicine Outpatient Clinic of Başakşehir Çam and Sakura City Hospital (HbA1c > 7%: n = 37; HbA1c < 7%: n = 101) and 118 healthy control subjects. HbA1c, white blood cell (WBC) count, NLR, MLR, and PLR values obtained at baseline and follow-up outpatient visits were retrospectively retrieved from the hospital information system and compared between groups.

Results

Glucose and HbA1c levels differed significantly among the groups, with the highest values observed in the uncontrolled diabetes group (p < 0.001). WBC and neutrophil counts were also significantly higher in patients with uncontrolled diabetes (p < 0.001). Monocyte counts, as well as NLR and MLR levels, were significantly increased in this group (p < 0.05). At the third-month follow-up, patients in the uncontrolled diabetes group exhibited significant changes in glucose, HbA1c, neutrophil, lymphocyte, NLR, and PLR levels (p < 0.05), whereas the change in MLR did not reach statistical significance (p = 0.083). Correlation analysis demonstrated significant positive associations between diabetes duration, glucose, and HbA1c levels and both NLR and MLR (r = 0.316–0.354, p < 0.001). Additionally, moderate positive correlations were observed among NLR, MLR, and PLR at both baseline and third-month measurements (p < 0.001).

Conclusion

NLR, MLR, and PLR are low-cost and easily accessible inflammatory markers that change in parallel with HbA1c levels and may be useful for monitoring glycemic control and disease progression in T2DM. These findings support the potential clinical utility of inflammation-based risk assessment in patients with type 2 diabetes mellitus.

Clinical trial number

Not applicable.

Introduction

Type 2 diabetes mellitus (T2DM) is a metabolic disorder characterized by chronic hyperglycemia resulting from inadequate insulin secretion, impaired insulin action, or a combination of both. Accounting for approximately 90–95% of all diabetes cases worldwide, T2DM has become one of the leading chronic diseases imposing a substantial economic and societal burden on healthcare systems. Chronic inflammation plays a pivotal role in the pathogenesis of T2DM by promoting insulin resistance and pancreatic β-cell dysfunction, ultimately leading to impaired glycemic control [1].

Plasma glycated hemoglobin A1c (HbA1c) is a well-established and reliable parameter widely used to assess long-term glycemic control in patients with diabetes. Elevated HbA1c levels are closely associated with poor disease control and an increased risk of diabetes-related complications. In recent years, accumulating evidence has demonstrated that inflammatory processes are critically involved in the pathophysiology of T2DM, often preceding the clinical onset of the disease and contributing to its progression [2, 3].

Beyond being a metabolic disorder, T2DM is a complex systemic disease associated with a wide range of microvascular and macrovascular complications [4]. Hyperglycemia- and insulin resistance–induced proinflammatory pathways play a major role in the development of these complications. Activation of various immune cells leads to a state of chronic, low-grade inflammation, which has been shown to correlate not only with the development of T2DM but also with disease progression and the severity of its complications [5].

Inflammation is now recognized as a key mechanism in the pathogenesis of many chronic diseases, extending far beyond infectious conditions. Among routinely available hematological parameters, the neutrophil-to-lymphocyte ratio (NLR), monocyte-to-lymphocyte ratio (MLR), and platelet-to-lymphocyte ratio (PLR) have emerged as accessible biomarkers reflecting systemic inflammatory status [6, 7]. Previous studies have reported significant elevations in NLR and MLR in various chronic conditions, including malignancies, acute coronary syndromes, chronic kidney disease, diabetic nephropathy, and chronic obstructive pulmonary disease [8, 9]. Notably, NLR has been highlighted as an early marker of subclinical inflammation and disease progression, making it a potentially valuable indicator for assessing inflammatory burden in metabolic disorders such as T2DM [10]. Several studies have further emphasized a significant association between elevated NLR levels and both microvascular and macrovascular complications related to diabetes [1].

In this context, the present study aimed to investigate the relationship between HbA1c levels and the inflammatory markers NLR, MLR, and PLR in patients with T2DM, both with and without adequate glycemic control, as well as in individuals without chronic disease. In addition, we sought to evaluate the potential utility of these low-cost and readily accessible inflammatory indices in the clinical management and monitoring of disease progression in T2DM. Importantly, whereas previous studies have primarily focused on the association between HbA1c and NLR at a single time point, our study simultaneously examines NLR, MLR, and PLR, and further assesses their short-term changes over a three-month follow-up period. This approach provides a more comprehensive perspective on the dynamics of inflammation in relation to glycemic control.

Materials and methods

This study was conducted in accordance with the ethical principles of the Declaration of Helsinki and was approved by the Clinical Research Ethics Committee of Başakşehir Çam and Sakura City Hospital (Approval No: 28.08.2024/196). This retrospective case–control with longitudinal follow-up study evaluated patients who attended the Internal Medicine Outpatient Clinic of Başakşehir Çam and Sakura City Hospital between October 2024 and December 2024. Patient data were retrospectively obtained from the hospital information management system and laboratory records in electronic format.

Patients with a newly established or previously diagnosed T2DM were included in the study. In addition, individuals without any known chronic disease who attended the outpatient clinic during the same period were included as the control group. Patients younger than 30 years or older than 80 years, pregnant women, and individuals with malignancy, subacute and chronic infections, obesity, smoking and renal failure, autoimmune disease, or refractory heart failure were excluded from the study.

Baseline data at the initial outpatient visit and follow-up data obtained at the 3-month control visit were retrieved from patient records. The collected variables included age, sex, duration of diabetes, use of insulin and/or oral antidiabetic drugs (OADs), HbA1c levels, fasting plasma glucose, hemoglobin, WBC, platelet count, neutrophil, lymphocyte, and monocyte counts. Inflammatory indices, including the NLR, MLR, and PLR, were calculated from complete blood count parameters.

Patients with T2DM were stratified into two groups based on glycemic control: controlled diabetes (HbA1c < 7%) and uncontrolled diabetes (HbA1c ≥ 7%). Biochemical and hematological parameters were compared between these groups.

Statistical analysis

Statistical analyses were performed using IBM SPSS Statistics (IBM Corp., Armonk, NY, USA). A p value of < 0.05 was considered statistically significant. Prior to the study, an a priori sample size and power analysis was conducted using G*Power to determine the minimum required sample size. Based on an expected effect size of 0.407, a statistical power of %95 and an alpha level of 0.05, the required sample size was calculated as 256 participants. The final sample size of 256 patients was obtained.

Normality of continuous variables was assessed using the Shapiro–Wilk test. As the data did not meet the assumption of normal distribution, non-parametric statistical methods were applied. Descriptive statistics were presented as median and minimum–maximum values. Comparisons between two independent groups were conducted using the Mann–Whitney U test, while comparisons among more than two independent groups were performed using the Kruskal–Wallis H test, followed by Dunn–Bonferroni post hoc analysis when appropriate. The Wilcoxon signed-rank test was used to compare dependent (paired) measurements. Spearman’s rank correlation analysis was performed to assess the strength and direction of associations between variables.

Results

A total of 256 patients were included in the study. The mean age of patients in the uncontrolled diabetes mellitus (DM) group was significantly higher than that of the control group (p < 0.001) (Table 1). Glucose and HbA1c levels differed significantly among the groups, with the highest values observed in the uncontrolled DM group (p < 0.001).

Table 1.

Comparison of baseline characteristics among study groups

	Control	Controlled DM	Uncontrolled DM	p
Age (years)	44.5 (22–75) ab	54(32–74)a	56(25–80) b	0.000
Diabetes duration (months)	0 (0–0) ab	72(7-480)a	120(1-360) b	0.000
GLU1 (mg/dl)	92(74–133)a	114(78–185)a	164(82–421)a	0.000
HBA1C1	5.5(4.5–5.9)a	6.5(6.5–6.9)a	8.4(7-14.7)a	0.000
WBC1 (10^3/µL)	7.22(4.5-11.53)	7.77(4.66–14.96)a	8.35(4.32–15.42)a	0.000
HB1 (g/dL)	13(9-16.7)	13.3 (10.4–15.8)	13.7 (8.9–17.1)	0.115
PLT1 (10^3/µL)	280 (151–434)	276 (160–525)	278 (157–522)	0.878
NEU1 (10^3/µL)	3.98 (1.89–7.25) ab	4.54 (2.7-10.72)a	5.05 (2.41–11.01) b	0.000
LYMPH1 (10^3/µL)	2.47 (1.29–5.36)	2.39 (1.51–4.12)	2.36 (1.01–4.2)	0.660
MONO1 (10^3/µL)	0.54 (0.18–0.97) ab	0.65 (0.35–1.05)a	0.61 (0.25–1.94) b	0.004
NLR1	1.67 (0.72–2.74)a	1.87 (0.83–4.32)	2.15 (0.88–5.03)a	0.000
MLR1	0.23 (0.09–0.49)a	0.24 (0.14–0.47)	0.26 (0.1–1.09)a	0.003
PLR1	112.61 (62.86–200)	107.95 (60.44- 205.88)	120.89 (52.78–260)	0.310

Groups marked with different superscripts (^a-b) indicate statistically significant differences between groups as determined by post hoc analysis. GLU, glucose; HbA1c, glycated hemoglobin; WBC, white blood cell count; HB, hemoglobin; PLT, platelet count; NEU, neutrophil count; LYMPH, lymphocyte count; MONO, monocyte count; NLR, neutrophil-to-lymphocyte ratio; MLR, monocyte-to-lymphocyte ratio; PLR, platelet-to-lymphocyte ratio

WBC and neutrophil counts were significantly higher in the uncontrolled DM group compared with the other groups (p < 0.001). In contrast, no statistically significant differences were observed among the groups with respect to hemoglobin, platelet, or lymphocyte counts (p > 0.05).

Monocyte counts and inflammatory markers, including the NLR and MLR, were significantly elevated in the uncontrolled DM group (p = 0.004, p < 0.001, and p = 0.003, respectively). However, no statistically significant difference was detected between the groups in terms of the PLR (p = 0.310). These findings are summarized in Figs. 1, 2 and 3.

Fig. 1.

Neutrophil-to-lymphocyte ratio (NLR) levels in healthy controls, controlled diabetes mellitus (DM), and uncontrolled DM patients

Fig. 2.

Monocyte-to-lymphocyte ratio (MLR) levels in healthy controls, controlled diabetes mellitus (DM), and uncontrolled DM patients

Fig. 3.

Platelet-to-lymphocyte ratio (PLR) levels in healthy controls, controlled diabetes mellitus (DM), and uncontrolled DM patients

In the controlled DM group, no statistically significant differences were observed between baseline and 3-month follow-up values for any of the evaluated parameters (all p > 0.05) (Table 2). In contrast, in the uncontrolled DM group, comparisons between baseline and 3-month measurements revealed statistically significant changes in glucose, HbA1c, neutrophil count, lymphocyte count, NLR, and PLR levels (p = 0.037, p < 0.001, p = 0.021, p < 0.001, p < 0.001, and p = 0.004, respectively). No significant differences were observed for WBC, hemoglobin, platelet count, monocyte count, or MLR (all p > 0.05), including MLR, which did not reach statistical significance (p = 0.083).

Table 2.

Comparison of baseline and 3-month values in controlled and uncontrolled diabetes mellitus (DM) patients

	Controlled DM		P	Uncontrolled DM		P
	0. mo	3. mo		0. mo	3. mo
GLU	114 (78–185)	115 (77–205)	0.478	164 (82–421)	156 (81–405)	0.037
HBA1C	6.5 (6.5–6.9)	6.3 (5.5–8.5)	0.088	8.4 (7- 14.7)	7.9 (5.5–12.2)	0.000
WBC	7.77 (4.66–14.96)	8.05 (5.56–12.11)	0.925	8.35 (4.32–15.42)	8.36 (4.33–14.07)	0.391
HB	13.3 (10.4–15.8)	13.5 (10.6–17)	0.118	13.7 (8.9–17.1)	13.3 (8.5–17)	0.393
PLT	276 (160–525)	272 (176–389)	0.350	278 (157–522)	284 (144–457)	0.715
NEU	4.54 (2.7- 10.72)	4.55 (2.92–8.25)	0.736	5.05 (2.41–11.01)	4.82 (2.27–9.76)	0.021
LYMPH	2.39 (1.51–4.12)	2.56 (1.51–4.5)	0.070	2.36 (1.01–4.2)	2.51 (0.96–4.34)	0.001
MONO	0.65 (0.35–1.05)	0.62 (0.36–1.16)	0.806	0.61 (0.25–1.94)	0.61 (0.31–1.27)	0.495
NLR	1.87 (0.83–4.32)	1.77 (0.69–3.47)	0.172	2.15 (0.88–5.03)	1.88 (0.63–4.34)	0.000
MLR	0.24 (0.14–0.47)	0.23 (0.15–0.43)	0.215	0.26 (0.1–1.09)	0.25 (0.11–0.53)	0.083
PLR	107.95 (60.44- 205.88)	104.69 (54.91- 206.41)	0.423	120.89 (52.78–260)	110.27 (63.76- 233.33)	0.004

GLU, glucose; HbA1c, glycated hemoglobin; WBC, white blood cell count; HB, hemoglobin; PLT, platelet count; NEU, neutrophil count; LYMPH, lymphocyte count; MONO, monocyte count; NLR, neutrophil-to-lymphocyte ratio; MLR, monocyte-to-lymphocyte ratio; PLR, platelet-to-lymphocyte ratio

According to the Spearman correlation analysis, diabetes duration demonstrated a very strong positive correlation with HbA1c1 (r = 0.819, p < 0.001) and a strong positive correlation with Glucose1 (r = 0.736, p < 0.001). Its associations with age (r = 0.448, p < 0.001) and NLR1 (r = 0.354, p < 0.001) were moderate, whereas the correlation with MLR1 (r = 0.228, p < 0.001) was weak but statistically significant. Glucose1 showed a very strong positive correlation with HbA1c1 (r = 0.837, p < 0.001) and a moderate positive correlation with NLR1 (r = 0.314, p < 0.001). Notably, HbA1c1 demonstrated a moderate positive association with NLR1 (r = 0.316, p < 0.001), while its relationship with MLR1 was weaker. No direct correlation between HbA1c1 and PLR1 was observed at baseline. Among inflammatory markers, NLR1 exhibited moderate positive correlations with both PLR1 (r = 0.542, p < 0.001) and MLR1 (r = 0.526, p < 0.001). Additionally, MLR1 and PLR1 were moderately correlated (r = 0.364, p < 0.001), indicating internal consistency among inflammatory indices rather than uniform associations with glycemic parameters. At the three-month follow-up, Glucose2 and HbA1c2 remained strongly correlated (r = 0.600, p < 0.001). NLR2 demonstrated moderate positive correlations with both MLR2 (r = 0.577, p < 0.001) and PLR2 (r = 0.493, p < 0.001). Overall, these findings suggest that NLR and to a lesser extent MLR at baseline are associated with glycemic control, whereas PLR appears to be more closely related to other inflammatory markers and may reflect dynamic changes over time rather than a direct relationship with HbA1c.

Discussion

Although HbA1c is widely used as a primary parameter for monitoring metabolic control in patients with diabetes mellitus, it is well recognized that this marker alone may be insufficient to fully capture the pathogenesis and progression of microvascular and macrovascular complications over the long-term course of the disease. Chronic low-grade inflammation has increasingly been shown to play a key role in the development of type 2 diabetes-related complications, such as diabetic nephropathy, proliferative diabetic retinopathy, and diabetic peripheral neuropathy. In this context, readily accessible and cost-effective systemic inflammatory markers, including NLR, MLR, and PLR, have attracted attention due to their associations with both malignancies and diabetes-related complications, particularly diabetic nephropathy. This study aimed to evaluate the relationship between these inflammatory indices and HbA1c, exploring their potential contribution as additional biomarkers reflecting the inflammatory burden of diabetes and the risk of complications beyond glycemic control.

In our study, the mean age of the uncontrolled DM group was higher than that of the controlled DM group. Consistently, fasting glucose and HbA1c levels were significantly elevated in the uncontrolled group, suggesting that glycemic control may become more challenging with advancing age. This is in line with the large-scale study by Selvin et al., which reported poorer glycemic control among individuals aged 65 years and older. Our findings support the literature and underscore the influence of age on diabetes management and glycemic regulation [11].

We also observed significantly higher NLR and MLR levels in the uncontrolled DM group compared to the controlled group. Similarly, Dayama et al. reported elevated NLR and MLR levels in patients with uncontrolled T2DM. These findings support the concept that type 2 diabetes should be considered not only as a metabolic disorder but also as a systemic disease characterized by chronic low-grade inflammation. The association of increased inflammatory response with poor glycemic control suggests that NLR and MLR may serve as potential biomarkers reflecting the inflammatory burden of diabetes and the risk of complications.

Our study demonstrated a positive correlation between HbA1c levels and both NLR and MLR, consistent with the findings of Sefil et al., who reported a significant positive relationship between HbA1c and NLR in poorly controlled diabetes patients [12]. These results indicate that the inflammatory response increases in parallel with glycemic dysregulation, supporting the critical role of inflammation in the pathogenesis and progression of diabetes. Therefore, systemic inflammatory markers such as NLR and MLR may serve as early indicators for predicting disease progression and complication risk in patients with inadequate glycemic control.

While most studies assess inflammatory markers at a single time point, our study identified significant changes in NLR and PLR at the three-month follow-up in the uncontrolled DM group. These findings suggest that these inflammatory parameters not only reflect disease status but may also provide clinically meaningful information through their temporal dynamics. Indeed, Yazan et al. reported significant associations between HbA1c and both NLR and PLR [13]. Our findings indicate that NLR and PLR reflect an inflammatory response that parallels glycemic control and may serve as dynamic biomarkers for monitoring treatment response, thereby supporting clinical decision-making.

The present study has several limitations that should be acknowledged. First, the retrospective case–control design may introduce selection bias and limits the ability to establish causal relationships between glycemic control and inflammatory markers. Second, the study was conducted at a single center with a relatively limited sample size, which may reduce the generalizability of the findings. In addition, unequal group sizes may have affected the robustness of intergroup comparisons. Although significant associations were observed between HbA1c and inflammatory markers, the analyses were primarily univariate, and adjustment for potential confounders such as age, diabetes duration, treatment modality, and comorbid conditions was not feasible because of the retrospective nature of the study and incomplete clinical data. Furthermore, information regarding treatment modifications and medication adherence during the 3-month follow-up period was not consistently available, limiting the interpretation of longitudinal changes in inflammatory markers. Measurements of NLR, MLR, and PLR were obtained at limited time points and may not fully reflect temporal biological variability. Therefore, the observed associations should be interpreted cautiously, and larger prospective studies with multivariable analyses are needed to confirm the independent clinical utility of these inflammatory markers in patients with T2DM.

In conclusion, this study demonstrates that inflammatory markers particularly NLR and MLR are significantly associated with poor glycemic control in patients with uncontrolled T2DM, while PLR may exhibit temporal variation during short term follow-up. These findings reinforce the concept that chronic low-grade inflammation is closely linked to deteriorating glycemic regulation. Given that NLR, MLR, and PLR are inexpensive, easily accessible, and routinely measured laboratory parameters, they hold promise as practical and supportive inflammatory indicators for monitoring glycemic status, assessing disease progression, and potentially aiding in the early detection of complications in clinical practice. However, considering the retrospective design, the relatively modest strength of the observed associations, and the absence of comprehensive adjustment for confounding variables, these markers should not yet be regarded as definitive tools for clinical decision making. Therefore, large-scale, prospective studies are warranted to establish their independent prognostic value and to clarify their role in the routine follow-up and management of patients with T2DM.

Author contributions

EDK, GS and BC conceived and designed the study. EDK drafted the initial version of the manuscript. EDK, GS, BC, and İA collected the data. İA performed the data analysis and translated the manuscript into English. All authors read and approved the final manuscript.

Funding

The authors declared that this study received no financial support.

Data availability

All data will be available by the correspondingauthor in a reasonable request.

Declarations

Ethics approval and consent to participate

Clinical Research Ethics Committee of Basaksehir Cam And Sakura City Hospital (Approval No: 28.08.2024/196). This study is retrospective in nature and utilizes only archival records and existing patient data. Since the data were analyzed in an anonymized manner, the requirement for obtaining informed consent was waived by the ethics committee in accordance with the “Regulation on Clinical Research” (Official Gazette: 27.05.2023/32203) and relevant national legislationIt was conducted in accordance with the ethical principles outlined in the Declaration of Helsinki.

Informed concent / consent for publication

our study was retrospective in design and the data were obtained only from the hospital database, no identifiable personal or clinical information was included in the manuscript. Therefore, informed consent for publication from individual participants was not required. Accordingly, the statement “Not Applicable” has been added to this section.

Competing interests

The authors declare no competing interests.