Reference intervals for serum cystatin C and serum creatinine in an adult sub-Saharan African population.

Background: Serum cystatin C (SCysC) and serum creatinine (SCr) are two biomarkers used in common practice to estimate the glomerular filtration rate (GFR). For SCysC and SCr to be used in a given population, normal values need to be determined to better assess patients. This study aimed to determine SCysC and SCr reference intervals (RIs) in a Cameroonian adult population and factors susceptible of influencing them.

Methods: We carried-out a cross-sectional study from November 2016 to May 2017 in Yaoundé, Cameroon. Participants were Cameroonians aged 18 years and above, residing inside the country and found in good health at study inclusion. SCysC and SCr were determined by particle-enhanced turbidimetric immunoassay standardized against the ERM-DA471/IFCC reference material and by the IDMS reference modified Jaffe kinetic method, respectively. RIs were determined using the 2.5th and 97.5th percentiles and their respective 90% confidence intervals (CIs). The quantile regression served to identify potential factors likely influencing SCysC and SCr values.

Results: We included 381 subjects comprising 49.1% females.. RIs for SCysC varied between 0.57 (90%CI: 0.50-0.60) and 1.03 mg/L (90%CI: 1.00-1.10) for females, and from 0.70 (90%CI: 0.60-0.70) to 1.10 mg/L (90%CI: 1.10-1.20) for males. Concerning SCr, its RIs ranged from 0.58 (90%CI: 0.54-0.61) to 1.08 mg/dL (90%CI: 1.02-1.21) for females, and from 0.74 (90%CI: 0.70-0.80) to 1.36 mg/dL (90%CI: 1.30-1.45) for males. Men had significantly higher SCysC and SCr values than women (p <  0.001). Likewise, subjects aged 50 years and above had higher SCysC values in comparison to younger age groups (p <  0.001), which was not the case for SCr values (p = 0.491). Moreover, there was a positive and significant correlation between SCysC and SCr in women (ρ = 0.55, p < 0.001), in men (ρ = 0.39, p < 0.001) and globally (ρ = 0.58; p < 0.001). Furthermore, the sex influenced both biomarkers' values across all quantile regression models while age and body surface area (BSA) influenced them inconsistently.

Conclusion: This study has determined serum cystatin C and serum creatinine reference intervals in an adult Cameroonian population, whose interpretations might take into account the patient's sex and to a certain extent, his/her age and/or BSA.