Establishment of reference intervals of biochemical analytes for South African adults: a study conducted as part of the IFCC global multicentre study on reference values

Abstract

Objective: This study was conducted as a part of the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) global study for establishing reference intervals (RIs) of common laboratory tests for the South African population considering gender, ethnicity, age and body mass index (BMI).
Methods: The researchers recruited 1 143 apparently healthy volunteers aged 18–65: 551 African (Afr) and 592 non-African (NAfr) (comprising 383 Caucasian and 209 Mixed Ancestry). Serum samples were measured for 40 chemistry and immunochemistry analytes. The standard deviation ratio (SDR) guided the need for partitioning reference values according to gender, ethnicity and age using a threshold of ≥ 0.4. The latent abnormal values exclusion (LAVE) method was applied to reduce influences of latent diseases before deriving RIs using both parametric and non-parametric methods.
Results: Based on SDR sex, males showed higher albumin, uric acid, creatinine, AST, CK and ferritin. Based on SDRRC, Afr compared to NAfr showed (i) higher total protein, amylase, CRP, immunoglobulin G and A and (ii) lower total bilirubin, total cholesterol, low-density lipoprotein cholesterol (LDL-C), ALT and cholinesterase. Both age-related changes in glucose and LDL-C, and BMI-related changes in ALT, ALP and LDH were more prominent in NAfr. RIs were determined according to gender, age and ethnicity. The LAVE method was effective in lowering the upper RI limits (UL) of nutritional markers such as γGT and CRP. Compared to the non-parametric method, the parametric method gave narrower confidence intervals of ULs for analytes with skewed distributions.
Conclusion: Establishing RIs by considering ethnicity was essential in many analytes in South Africa. Age and BMI-related changes differed greatly between Afr and NAfr.