High levels of platelet-to-lymphocyte ratio may predict reduced risk of end stage of renal disease in Chinese patients with MPO-ANCA associated vasculitis

Abstract

Objective

Platelet-to-lymphocyte ratio (PLR) has recently been investigated as a new inflammatory marker in many inflammatory diseases, including systemic lupus erythematosus and immunoglobulin A vasculitis. However, there were very few reports regarding the clinical role of PLR in patients with anti-neutrophil cytoplasmic antibody (ANCA) associated vasculitis. This study was thus undertaken to investigate the relationship between inflammatory response and disease activity in Chinese patients with myeloperoxidase-anti-neutrophil cytoplasmic antibody (MPO-ANCA) associated vasculitis. Furthermore, we evaluated whether PLR predicts the progression of end stage of renal disease (ESRD) and all-cause mortality.

Methods

The clinical, laboratory and pathological data, and the outcomes of MPO-ANCA associated vasculitis patients were collected. The Spearman correlation coefficient was computed to examine the association between 2 continuous variables. Cox regression analysis was used to estimate the association between PLR and ESRD or all-cause mortality.

Results

A total of 190 consecutive patients with MPO-ANCA associated vasculitis were included in this study. Baseline PLR was positively correlated with CRP (r=0.333, P<0.001) and ESR (r=0.218, P=0.003). PLR had no obvious correlation with Birmingham Vasculitis Activity Score (BVAS). Patients having PLR≥330 exhibited better cumulative renal survival rates than those having PLR<330 (P=0.017). However, there was no significant difference in the cumulative patient survival rates between patients with PLR≥330 and those with PLR<330 at diagnosis (P>0.05). In multivariate analysis, PLR is associated with the decreased risk of ESRD (P=0.038, HR=0.518, 95% CI 0.278 to 0.963). We did not find an association between PLR with all-cause mortality using multivariate analysis (HR=1.081, 95% CI 0.591 to 1.976, P=0.801).

Conclusion

PLR is positively correlated with CRP and ESR. Furthermore, PLR may independently predict the risk of ESRD.

Anti-neutrophil cytoplasmic antibody (ANCA)associated vasculitis is a potentially life-threatening and multisystemic small-vessel vasculitic disease^[1-2]. Microscopic polyangiitis (MPA), granulomatosis with polyangiitis (GPA), eosinophilic granulomatosis with polyangiitis (EGPA), and renal-limited vasculitis (RLV) are 4 major types of associated vasculitis^[3-4]. The major target antigens of ANCAs are myelo-peroxidase (MPO) and proteinase 3 (PR3), which are stored in the granules of neutrophils and lysosomes of monocytes. Renal involvement is common and typically manifested as rapidly progressive glomerulonephritis^[5].

As associated vasculitis causes inflammation of small blood vessels in the body, several inflammatory markers, such as C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) have been used to assess inflammatory status in associated vasculitis^[6]. The platelet-to-lymphocyte ratio (PLR) has recently been investigated as an indicator for prognostic prediction of diverse diseases such as cancer and inflammatory diseases^[7-9]. Recently, PLR has been demonstrated to be associated with disease activity and prognosis in patients with different forms of vasculitis^[10-12]. However, there were very few reports of the clinical role of PLR in patients with associated vasculitis. It has been suggested that PLR at diagnosis is associated with the inflammatory burdens in patients with associated vasculitis^[13]. Nevertheless, there is a lack of data in the literature about the prognosis potential of PLR for end stage of renal disease (ESRD) and all-cause mortality in patients with associated vasculitis.

Furthermore, the disease spectrum of associated vasculitis and the major target antigen of ANCAs in Chinese patients are quite different from those in European and American populations. MPA is the dominant form of associated vasculitis in China. Accordingly, MPO instead of PR3 is the major target ANCA antigen in Chinese associated vasculitis patients^[14]. Furthermore, significant difference between PR3 associated vasculitis patients and MPO-ANCA associated vasculitis patients has been demonstrated and the evidence is accumulating that PR3 associated vasculitis and MPO-ANCA associated vasculitis are 2 distinct diseases^[15-17].

Therefore, the aim of this study was to investigate the relationship between PLR at diagnosis and inflammatory response and disease activity among MPO-ANCA associated vasculitis patients in a single Chinese center. Furthermore, we evaluated whether PLR could predict the progression of ESRD and all-cause mortality.

1. Subjects and methods

1.1. Study design

This was a retrospective observational study. The study was conducted in accordance with the Declaration of Helsinki. All procedures performed in studies involving human participants were in accordance with the ethical standards of the Ethics Committee of Xiangya Hospital of Central South University and with the 1964 Declaration of Helsinki and its later amendments or comparable ethical standards. Because of the retrospective nature of the research, the requirement for informed consent was waived.

1.2. Study population

This retrospective study included all patients with MPO-ANCA associated vasculitis, who were diagnosed from January 2010 to November 2019 in the Department of Nephrology and Department of Rheumatology and Immunology, Xiangya Hospital，totally 190 patients. All patients fulfilled the 2012 Chapel Hill Consensus Conferences Nomenclature of vasculitis and were then reclassified based on the algorithm suggested by the European Medicines Agency in 2007^[18-19]. Exclusion criteria were as follows: 1) EGPA or secondary vasculitis; 2) comorbid kidney diseases, such as IgA nephropathy; 3) the coexistence of another autoimmune disease; 4) the coexistence of infection when the diagnosis of associated vasculitis was made; 5) Hepatitis B virus, hepatitis C virus infection. The study protocol was approved by the Ethic Committee of Xiangya Hospital (IRB approval number 201212002). Informed consent was obtained from each patient included in the study.

Baseline demographic data and laboratory parameters were reviewed from the electronic medical record system in the hospital. The estimated glomerular filtration rate (eGFR) was determined as described previously^[20]. Disease activity was determined by the Birmingham Vasculitis Activity Score (BVAS)^[21]. The serum ANCA level was detected by both indirect immunofluorescence (IIF) assay (Euroimmun, Lübeck, Germany) and antigen-specific ELISA (Inova Diagnostics, San Diego, USA) for PR3-ANCA and MPO-ANCA in all patients.

1.3. Kidney histopathology

Fifty-nine out of the 190 (31.05%) patients received a kidney biopsy at the time of diagnosis and before the commencement of immunosuppressive therapy. Biopsies were independently scored by 2 pathologists using direct immune fluorescence and light microscopy. The biopsy specimens were assigned to 4 categories based on the definition of the 2010 histological classification^[22]. All the specimens met the requirement of a minimum of 10 whole glomeruli^[22]. Tubulointerstitial lesions such as interstitial fibrosis and tubular atrophy were graded semiquantitatively, as previously reported^[23].

1.4. Treatment

As described previously^{[1, 3]}, all the patients received the standard induction therapy including oral prednisone combined with cyclophosphamide (CTX). Briefly, oral prednisone was prescribed initially at a dosage of 1 mg/kg, with a gradual reducing to 12.5- 15.0 mg by 3 months. CTX was administered intravenously 0.50-0.75 g/m² every month or daily oral dose of 2 mg/kg. A 25% dose reduction of CTX was carried out for those over 65 years or those with GFR <20 mL/(min·1.73 m²), and CTX was temporarily withdrawn for patients who developed leukocytopenia (less than 4×10⁹/L). Some patients with rapidly progressive glomerulonephritis or pulmonary haemorrhage received methylprednisolone pulse therapy before standard induction therapy and/or additional plasma exchanges before the above-mentioned standard induction therapy. Intravenous CTX every 3 months or daily oral azathioprine (AZA) or mycophenolate mofetil (MMF) was given for maintenance therapy.

1.5. Outcome measures

The clinical outcome variables were ESRD and all-cause mortality. ESRD was defined by dialysis dependence for greater than 3 months or kidney transplantation. We also counted all-cause death in associated vasculitis patients.

1.6. Statistical analysis

PLR was calculated as the ratio between the absolute platelet count and lymphocyte count obtained at the time of evaluation. We identified the cut-off point for PLR level using maximally selected log-rank statistics^[24]. All continuous variables are presented as mean±standard deviation ( $\overline{x}$ ±s) or median with interquartile range [M(P ₂₅, P ₇₅)]. Categorical variables are presented as frequencies. Analyses were performed using SPSS statistical software (version 23.0). The normality of distribution was checked by Kolmogorov-Smirnov test. To compare the difference between 2 groups when the continuous data fitted a normal distribution, an unpaired Student's t-test was used. To compare the differences for nonparametric data between the groups, Mann-Whitney U test was used. Chi-square tests or Fisher's exact tests was used to compare the differences among groups for categorical measures. Spearman correlation coefficient was used to examine the correlation between 2 continuous variables. Kaplan-Meier analysis was used to assess patient and kidney survival. The log-rank test was used to evaluate differences among groups. Univariate and multivariate Cox regression models were used to assess the association between PLR and the kidney survival and all-cause mortality. A P<0.05 (2-sided) was considered significant.

2. Results

2.1. Baseline characteristics of the patients

The cut-off point for the PLR level for ESRD was 330 (Figure 1). MPO-ANCA associated vasculitis patients were divided into a high PLR (PLR≥330) and a low PLR (PLR<330) group and baseline demographics and biochemical measurements are summarized in Table 1. MPO-ANCA associated vasculitis patients with high PLR (above the cut-off value) had higher serum levels of CRP and ESR, and older age, but lower serum levels of albumin.

Figure 1. Maximally selected log-rank statistics for cutoff point of platelet-to-lymphocyte ratio The cut-off point of the platelet-to-lymphocyte ratio level for ESRD is 330.

Table 1.

Baseline demographic characteristics of MPO-ANCA associated vasculitis patients according to platelet-to-lymphocyte ratio

Variables	PLR<330	PLR≥330	P
Age/years	57.43±15.67	63.13±8.72	0.002
Male/female/No.	83/62	22/23	0.325
MPA/GPA/RLV/No.	135/3/7	40/4/1	0.082
Median follow-up/month	17(8, 32)	17(6, 32)	0.558
White blood cells/(109·L-1)	9.56±4.28	11.34±5.90	0.065
Hemoglobin/(g·L-1)	81.74±20.76	82.04±19.32	0.930
Platelet/(×109·L-1)	234.65±105.76	303.84±114.00	<0.001
Neutrophil/(×109·L-1)	7.53±4.42	9.84±5.70	0.016
Lymphocyte/(×109·L-1)	1.50±1.01	0.69±0.30	<0.001
Serum albumin/(g·L-1)	36.4(28.4, 58.9)	28.5(24.8 56.9)	0.009
Serum globulin/(g·L-1)	29.1(26.1, 34.5)	32.6(25.9, 37.5)	0.544
Proteinuria/(g·d-1)	1.07(0.50, 1.82)	0.91(0.50, 1.62)	0.659
Serum creatinine/(μmol·L-1)	365.5(186.8, 593.0)	350.9(113.7, 504.0)	0.194
eGFR/(mL·min-1·1.73 m-2)	14.46(8.36, 36.55)	14.04(10.21, 53.54)	0.325
ESR/(mm·h-1)	66(38, 95)	88(49, 120)	0.043
CRP/(mg·L-1)	18.4(6.22, 66.80)	52.3(15.0,102.8)	<0.001
C3/(mg·L-1)	804.31±265.22	772.85±252.71	0.512
C4/(mg·L-1)	243.65±150.81	253.03±164.65	0.739
IgA/(mg·L-1)	2 559.58±1 186.77	2611.72±1477.18	0.821
IgG/(g·L-1)	14.07±4.66	15.02±5.09	0.275
IgM/(mg·L-1)	1 186.98±818.08	999.59±558.05	0.182
Organ involvement
Kidney/[No. (%)]	138(95.17)	43(95.56)	0.915
Pulmonary/[No. (%)]	80(55.17)	27(60.00)	0.568
Cardiovascular/[No. (%)]	25(17.24)	6(13.33)	0.535
Nerve system/[No. (%)]	38(26.21)	11(24.44)	0.873
BVAS/No.	16(12, 19)	15(11, 17)	0.519
EUVAS classification/No.
Focal	4	0	0.958
Mixed	19	4
Crescentic	17	3
Sclerotic	10	2
Tubulointerstitial injury/No.
Score 0	0	0	0.597
Score 1	27	5
Score 2	16	4
Score 3	7	0

Normal distribution data are presented as $\overline{x}$ ±s and non-normal distribution data are presented as M(P ₂₅, P ₇₅). eGFR: Estimated glomerular filtration rate; ESR: Erythrocyte sedimentation rate; CRP: C-reactive protein; C3: Complement 3; C4: Complement 4; IgA: Immunoglobulin A; IgG: Immunoglobulin G; IgM: Immunoglobulin M; BVAS: Birmingham Vasculitis Activity Score; EUVAS: European Vasculitis Society.

2.2. Correlations of PLR with disease activity and clinical characteristics of MPO-ANCA associated vasculitis patients

As shown in Table 2, PLR is positively correlated with CRP (r=0.333, P<0.0001) and ESR (r=0.218, P=0.003), and is not significantly associated with BVAS (r=-0.067, P=0.359).

Table 2.

Correlations of platelet-to-lymphocyte ratio (PLR) with laboratory findings in MPO-ANCA associated vasculitis patients

Laboratory indexes	PLR		Laboratory indexes	PLR
	r	P		r	P
White blood cells	0.110	0.129	CRP	0.333	<0.001
PLT	0.442	<0.001	C3	-0.028	0.714
Lymphocyte	-0.640	<0.001	C4	0.036	0.645
ESR	0.218	0.003	BVAS	-0.067	0.359

PLT: Platelet; ESR: Erythrocyre sedimentation rate; C3: Complement 3; C4: Complement 4; BVAS: Birmingham Vasculitis Activity Score.

2.3. High PLR is associated with decreased risk of ESRD

Cumulative renal survival and patient survival rates were depicted in Figure 2. Patients having PLR≥330 exhibited better cumulative renal survival rates than those having PLR<330 (P=0.017). However, there was no significant difference in the cumulative patient survival rates between patients having PLR≥330 and those PLR<330 at diagnosis (P>0.05).

Figure 2. Kaplan-Meier curve for renal survival (A) and all-cause mortality (B) of MPO-ANCA associated vasculitis patients according to binary of platelet-to-lymphocyte ratio (PLR).

In multivariate analysis, PLR had an association with decreased risk of ESRD (HR=0.518, 95% CI 0.278 to 0.963, P=0.038, Table 3). We did not find an association between PLR with all-cause mortality using multivariate analysis (HR=1.081, 95% CI 0.591 to 1.976, P=0.801).

Table 3.

Multivariate Cox regression analysis for the association between platelet-to-lymphocyte ratio (PLR) and end stage of renal disease

Variables	HR (95% CI)	P
eGFR	0.939(0.915-0.963)	<0.001
IgM	0.999(0.999-1.000)	0.007
Pulmonary involvement	1.738(1.056-2.860)	0.030
PLR	0.518(0.278-0.963)	0.038

eGFR: estimated glomerular filtration rate; IgM: Immunoglobulin M; HR: Hazard ratio.

3. Discussion

The key finding of this study is that patients with MPO-ANCA associated vasculitis and higher levels of PLR portend decreased risk of ESRD. Another important finding was that PLR was positively correlated with CRP and ESR in MPO-ANCA associated vasculitis patients. These findings indicate that as an easily measurable and available laboratory parameter, PLR may reflect inflammatory response and estimate prognosis during follow-up in MPO-ANCA associated vasculitis patients.

With the growing understanding of the role of inflammation in the pathogenesis of associated vasculitis, researchers have focused on markers for the evaluation of inflammatory burden of the disease. CRP, ESR, and WBC are common used noninvasive markers of inflammation. PLR is also an inflammatory index in routine blood test. PLR change may be associated with inflammation and cytokines. The absolute lymphocyte count is usually decreased in autoimmune diseases, and the platelet count is often increased in patients with associated vasculitis during the active disease state^[25-26]. However, the role of PLR in MPO-ANCA associated vasculitis patients remains unclear so far. The results of our study showed PLR was positively correlated with CRP. This data are consistent with previous work^[27] showing that PLR is positively correlated with inflammatory indices such as CRP in RA. We have also observed a positive correlation between PLR and ESR in MPO-ANCA associated vasculitis. These results suggested that the PLR might be one potential index reflecting the inflammatory response in MPO-ANCA associated vasculitis. However, no significant relationship between PLR and BVAS was observed in the present study, which suggested the value of PLR to predict and evaluate disease activity in patients with MPO-ANCA associated vasculitis remains elusive.

The decreased likelihood of ESRD in patients with higher PLR level versus patients with lower PLR level is in accord with our clinical experience. As mentioned above, PLR might be one potential index for reflecting the inflammatory response in MPO-ANCA associated vasculitis. Thus, the phenomenon resembles what is seen in malignant disease where highly active proliferating cells are more sensitive to initial chemotherapy^[28], and also findings in SLE patients with glomerulonephritis, patients with the highest activity index in renal biopsies were most likely to enter remission^[29].

Our study has several limitations. First, the relatively low rate of kidney biopsy might lead to some bias and reduce the power to demonstrate associations between PLR and kidney biopsy findings. The predominant reason for this low rate of kidney biopsy was that some patients had contraindications for kidney biopsy. Another important reason was that some patients refused to receive kidney biopsy. The second limitation of our research was the relatively short duration of follow-up. Third, with the retrospective nature of data collection, the maintaining immunosuppressive regimen was not unified. Finally, the number of MPO-ANCA associated vasculitis patients in this study was not large enough to represent the ethnic feature of Chinese patients with MPO-ANCA associated vasculitis. Therefore, further studies are required using a large cohort of patients to validate these results.

Contributions: HUANG Li Conception and design, collection, assembly, analysis, and interpretation of data, and manuscript writing; SHEN Chanjuan, CHEN Jinbiao Collection, assembly, analysis, and interpretation of data; ZHONG Yong Collection, assembly, analysis, and interpretation of data, and manuscript writing; Joshua D. Ooi Manuscript writing; Peter J. Eggenhuizen Collection and assembly of data; ZHOU Ya’ou, WU Ting, MENG Ting, XIAO Zhou, LIN Wei, TANG Rong, AO Xiang, XIAO Xiangcheng, ZHOU Qiaoling Provision of study materials or patients; XIAO Ping Administrative support and provision of study materials or patients.

Funding Statement

This work was supported by the Key Research and Development Program of Hunan province (2020WK2008), the Talent Scholars of Hunan Province for the Innovation of Science and Technology (2020RC5002), and the Natural Science Foundation of Hunan Province (2021JJ31130, 2020JJ5903), China.

Conflict of Interest

The authors declare that they have no conflicts of interest to disclose.

Note

http://xbyxb.csu.edu.cn/xbwk/fileup/PDF/202202211.pdf