Association between serum cystatin C and diabetic peripheral neuropathy: a cross-sectional study of a Chinese type 2 diabetic population

Objective: Serum cystatin C (CysC) is a sensitive marker of kidney function and recent studies have shown that CysC plays a critical role in degenerative diseases in both the central and the peripheral nervous systems. The aim of this study was to explore the relationship between serum CysC and diabetic peripheral neuropathy (DPN) in patients with type 2 diabetes. Methods: In total, 937 type 2 diabetic patients were enrolled in this cross-sectional study. Serum CysC concentration was measured by immunoturbidimetry. DPN was evaluated by neurological symptoms, neurological signs, neurothesiometer, and electromyogram. Results: Serum CysC levels were significantly higher in DPN patients (1.3 (1.1-1.5) mg/l) compared with patients with signs of DPN (1.1 (0.9-1.3) mg/l, P<0.001) and non-DPN patients (1.0 (0.9-1.3) mg/l, P<0.001). Multiple regression analysis revealed that DPN was associated with age, diabetes duration, HbA1c, and serum CysC. Spearman's correlation analysis showed that serum CysC was closely related with age, sex, diabetes duration, hypertension, glomerular infiltration rate, and serum creatinine (Cr) level. The patients were divided into quartiles according to the serum CysC levels. Compared with quartile 1 (referent), the risk of DPN was significantly higher in quartile 2 (odds ratio (OR), 1.753; 95% CI, 1.055-2.912; P<0.05), quartile 3 (OR, 2.463; 95% CI, 1.445-4.917; P<0.01), and quartile 4 (OR, 5.867; 95% CI, 2.075-16.589; P<0.01). Receiver-operating characteristic analysis revealed that the optimal cutoff point of serum CysC to indicate DPN was 1.25 mg/l in male patients and 1.05 mg/l in female patients. High serum CysC level indicated a onefold higher risk of DPN. Conclusions: High serum CysC level is closely associated with DPN and may be a potential biomarker for DPN in type 2 diabetic patients.