Population-specific reference intervals for cystatin C, creatinine and urea, and their impact on diagnostic classification and eGFR stratification in Nigerian adults.

Authors

Imafidor Iyabode, Bruno Basil, Izuchukwu Nnachi Mba, Jamila Aminu Mohammed, Maxwell Nwegbu, Amos Ali Gadzama

Published in

Clinical biochemistry. Pages 111203. Sep 12, 2026. Epub Sep 12, 2026.

Abstract

To establish population-specific reference intervals (RIs) for serum cystatin C, creatinine, and urea among healthy Nigerian adults and evaluate the potential diagnostic implications of applying manufacturer-derived RIs established in non-African populations.
A cross-sectional reference interval study was conducted among 243 apparently healthy adults (120 males and 123 females), aged 18-65 years, recruited in Abuja, Nigeria. Serum cystatin C, creatinine, and urea were measured using standardized laboratory methods. RIs were derived non-parametrically as the 2.5th-97.5th percentiles in accordance with CLSI C28-A3 recommendations. The need for sex-specific partitioning was assessed using the Lahti method. Diagnostic misclassification was evaluated by comparing classifications based on locally derived and manufacturer-provided RIs using McNemar's test. Estimated glomerular filtration rate (eGFR) was calculated using the CKD-EPI 2021 equations.
Creatinine and cystatin C required sex-specific partitioning, whereas urea did not. The combined RI for urea was 2.55-6.99 mmol/L. Creatinine RIs were 52.07-116.82 μmol/L in males and 44.47-96.23 μmol/L in females. Cystatin C RIs were 0.30-2.07 mg/L in males and 0.17-1.94 mg/L in females. Compared with locally derived RIs, manufacturer-derived intervals classified substantially more healthy individuals as abnormal for cystatin C (65.9% vs 5.8%; net reclassification +60.1%, p < 0.001) and female creatinine (52.5% vs 5.0%; +47.5%, p < 0.001), with minimal discordance for urea. Most participants (87.2%) were classified within KDIGO G1-G2 eGFR categories.
Locally derived kidney biomarker RIs differ substantially from manufacturer-provided intervals in this Nigerian population, particularly for cystatin C. Reliance on externally derived RIs may substantially overclassify kidney dysfunction and contribute to inappropriate clinical decision-making. Population-specific validation should be prioritized to improve diagnostic accuracy and CKD assessment in African populations.

PMID:
42731779
Bibliographic data and abstract were imported from PubMed on 13 Sep 2026.

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