Creatinine- vs. cystatin C-based equations compared with 99mTcDTPA scintigraphy to assess glomerular filtration rate in chronic kidney disease

In chronic kidney disease (CKD), accurate estimation of the glomerular filtration rate (GFR) is mandatory. Gold standard methods for its estimation are expensive and time-consuming. We compared creatinine- versus cystatin C-based equations to measure GFR, employing (99m)Tc-DTPA scintigraphy as the gold standard.

This was a prospective cross-sectional observational study including 300 subjects. CKD was defined according to K/DOQI guidelines, and patients were separated into groups: stage 1 (G1), n=26; stage 2 (G2), n=52; stage 3 (G3), n=90; stage 4 (G4), n=37; stage 5 (G5), n=60; and control group, n=35. Creatinine-based estimates were from 24-hour creatinine clearance using the Walser formula, Cockcroft-Gault, MDRD-4 and CKD-EPI; cystatin C equations used were Larsson, Larsson modified equation, Grubb and Hoek.

Age and body mass index were different among groups; proteinuria, hypertension, diabetes and primary glomerulopathies significantly increased as CKD worsened. In the global assessment, CKD-EPI and Hoek gave the highest correlations with (99m)Tc-DTPA: rho=0.826, p<0.001 and rho=0.704, p<0.001, respectively. Most significant linear regressions obtained: CKD-EPI vs. (99m)Tc-DTPA, Hoek vs. (99m)Tc-DTPA and CKD-EPI vs. Hoek. However, important differences emerged when each group was analyzed separately. Best significant correlations obtained with (99m)Tc-DTPA: control group, creatinine clearance rho=0.421, p=0.012; G1, Crockoft-Gault rho=0.588, p=0.003; G2, CKD-EPI rho=0.462, p<0.05; G3, CKD-EPI rho=0.508, p<0.001; G4, Hoek rho=0.618, p<0.001; G5, CKD-EPI rho=0.604, p<0.001.

At GFR <60 ml/min, CKD-EPI and Hoek equations appeared to best correlate with (99m)TcDTPA. In controls and at early stages of CKD, creatinine-based equations correlated better with (99m)Tc-DTPA, with CKD-EPI being the one with the best degree of agreement.