A decline in renal function suggests progression of
chronic kidney disease. This can be determined by measured GFR (e.g.,
iothalamate clearance), serum
creatinine (SCr)-based GFR estimates, or
creatinine clearance. A cohort of 234 patients with
autosomal dominant polycystic kidney disease and baseline
creatinine clearance>70 ml/min were followed annually for four visits.
Iothalamate clearance, SCr, and
creatinine clearance were obtained at each visit. Estimated GFR (eGFR) was determined with the Modification of Diet in Renal Disease (MDRD) and Cockcroft-Gault equations. Renal function slopes had a mean residual SD of 10.7% by
iothalamate clearance, 8.2% by MDRD equation, 7.7% by Cockcroft-Gault equation, and 14.8% by
creatinine clearance. By each method, a decline in renal function (lowest quintile slope) was compared among baseline predictors.
Hypertension was associated with a decline in
iothalamate clearance (odds ratio [OR] 5.8; 95% confidence interval [CI] 2.3 to 14), eGFR (OR [MDRD] 2.0 [95% CI 1.0 to 4.2] or OR [Cockcroft-Gault] 1.9 [95% CI 0.9 to 3.9]), and
creatinine clearance (OR 2.0; 95% CI 1.0 to 4.2). Each doubling of kidney volume at baseline was associated with a decline in
iothalamate clearance (OR 2.4; 95% CI 1.5 to 3.7), eGFR (OR 1.7 [95% CI 1.1 to 2.6] or 2.1 [95% CI 1.4 to 3.3]), and
creatinine clearance (OR 1.7; 95% CI 1.1 to 2.5). Predictor associations were strongest with measured GFR. Misclassification from changes in non-GFR factors (e.g.,
creatinine production, tubular secretion) conservatively biased associations with eGFR. Misclassification from method imprecision attenuated associations with
creatinine clearance.