Performance of creatinine and cystatin C-based equations to estimate glomerular filtration rate in African children with sickle cell anemia

BACKGROUND: Serum creatinine (SCr), the most used biomarker to evaluate glomerular filtration rate (GFR), might be inaccurate in children with sickle cell anemia (SCA). In this context, cystatin C (SCys) could be of interest. This study evaluated the performance of commonly used SCr- and SCys-based estimated GFR (eGFR) equations in African children with SCA.

METHODS: This cross-sectional study included 109 steady-state children with SCA aged 3-18 years, from the Democratic Republic of Congo. Measured GFR (mGFR) was obtained using iohexol plasma clearance. eGFR was calculated using commonly used SCr- and SCys-based equations in children. The performance of these equations was evaluated by calculating the bias, precision, and accuracy within 30% (P30) of mGFR.

RESULTS: The mean age of participants was 9.9 ± 4.2 years, and 48.6% were female. The median mGFR was 142 (IQR 119-169) mL/min/1.73 m2. Of the equations studied, the FAS-Age SCr had the lowest bias (0.9 mL/min/1.73 m2). However, the 95% limit of agreement was very wide (-80.3 to + 81.6). SCr failed to rise in an age-dependent manner, reflecting a progressive loss of muscle mass or increased tubular secretion. All SCys-based equations underestimated GFR and failed to detect hyperfiltration, but there was no age-related change in bias.

CONCLUSION: These data show that all common eGFR equations using SCr or SCys poorly predict mGFR in African children with SCA. SCr-based equations potentially miss a decline in kidney function, which suggests that SCys could be the preferred marker in this population.