Reference Interval of Serum Cystatin C in Dravidian Population Subset of South Asian Ethnic Groups: An Observational Cross-sectional Study

Abstract

Introduction: Serum Cystatin C (Cys C) facilitates to detect mild renal dysfunction and overall risk of death in older patients with chronic renal diseases. The requirement for creating a particular reference interval is mandatory for such renal diseases in South Asian population since the value of serum creatinine varies largely with age, gender and population/ethnicity and data of same is short for South Asian population. Aim: To determine the reference interval of serum Cystatin C amongst the Dravidian population subset of South Asian ethnic groups. Materials and Methods: This observational cross-sectional study was conducted in Department of Biochemistry and Transfusion Medicine at Government Medical College, Thrissur, Kerala, India, from July 2020 to January 2021 among on 235 healthy adults (20-60 years). A 4 mL of blood was drawn by aseptic precautions and serum was separated within three hours of blood collection. Serum Cys C was assayed by latex enhanced immunoturbidimetric cystatin C assay using a calibrator traceable to international standard European Specific Protein Reference Material (ERM DA-471) developed by the International Federation of Clinical Chemistry (IFCC) and Laboratory Medicine. Serum creatinine (sCr) by Jaffe method in a fully automatic clinical chemistry analyser. Categorical variables are presented using frequency (percentage) while continuous variables are summarized with an inter-percentile range. The Kolmogorov-Smirnov test was used to assess the normality of the distribution of continuous variables. Results: Total of 235 subjects (20-60 years of age, 17 males and 218 females) were included in the study. The non parametric reference intervals for Cys C were found to be from 0.39 to 0.79 mg% and that of sCr ranged from 0.79 to 1.2 mg%. The relationship between Cystatin C with age showed an increase in Cystatin C levels as age advances; Spearman's rank correlation coefficient (rho=0.197). The weak correlation between Cystatin C and sCr was also observed (rho=0.37; p-value <0.0001). Conclusion: The level of serum cystatin C (0.39 to 0.79 mg%) can be used as a diagnostic concentration reference interval of the protein that helps to recognise, standardise and establish it as a potential biomarker to detect renal disorders in South Asian ethnic population.