Serum Cystatin C And Creatinine As Markers Of Kidney Function In Adults In Enugu State, Nigeria

ABSTRACT

With the increasing recognition of the several pitfalls of serum creatinine (SCr) and

creatinine-based glomerular filtration rate (GFR) estimates as measures of kidney function, a

novel biomarker, cystatin C (Cys C) which is claimed to be superior to the creatinine-based

estimates has been proposed. However, this claim is yet to be validated in an indigenous black

setting. This study was therefore, to verify this claim and to assess the best method to estimate

GFR in a typical African black population. Three hundred (150 males and 150 females)

apparently healthy black subjects, aged 20 to 82 years, in Enugu metropolis, Enugu state were

used for the study, which was conducted between April and August 2010. Demographic and

anthropometric measurements were taken, fasting blood samples were collected and analyzed

for urea, albumin, creatinine and cystatin C using standard procedures. GFR was estimated

using six-published GFR equations —the Filler’s Cys C, standard Cockcroft and Gault (S-CG),

body surface area (BSA)-modified CG (B-CG) , original Modification of Diet in Renal Disease

(MDRD1) study, abbreviated MDRD (MDRD2) study, and the Mayo Clinic Quadratic (MCQ)

formulae. The performance of the SCr-based GFR equations relative to the Filler’s equation was

evaluated using four modalities — bias, precision, accuracy and correlation. The non-parametric

reference intervals (RI) for Cys C were 0.65 – 1.12 mg/L (median 0.86 mg/L) in males, 0.62 –

1.12 mg/L in females (median 0.85 mg/L) and 0.64 – 1.12 mg/L (median 0.86 mg/L) in all the

subjects. The non-parametric RI for SCr were 73 – 110 μmol/L (median 89 μmol/L) in males, 65 -

102 μmol/L (median 82 μmol/L) in females and 66 – 106 μmol/L (median 86 μmol/L) in all the

subjects. There was no significant difference between males and females in the Cys C levels and

reference intervals (p > 0.05). Overall, body indices showed an independent association with

Cys C levels, except for a modest association with body mass index (r = 0.15; p < 0.05), whereas

SCr levels were strongly associated with gender and body indices. Cys C- based GFR equation

appeared to estimate GFR best with a median GFR of 110 ml/min/1.73m2 (p < 0.0001), whereas

the CG formula appeared to perform best amongst the SCr-based GFR equations, and the

MDRD2 study equation was the worst performer. Our results suggest but cannot prove that Cys C may be a better marker of kidney function than creatinine, and that the CG equation remains the best SCr-based estimate of GFR in our setting. More work however, is recommended to

address other reported limitations of Cys C, and a GFR equation specially tailored to the needs of the indigenous black population is urgently needed.