Background: Autosomal dominant polycystic kidney disease (ADPKD) is characterized by renal tubular cell proliferation and dedifferentiation, which may influence tubular secretion of creatinine (CCr[TS]).
Study Design: Diagnostic test study.
Setting & Participants: We therefore investigated CCr(TS) in patients with ADPKD and controls and studied consequences for the performance of glomerular filtration rate (GFR) estimating equations.
Index & Reference Tests: In patients with ADPKD and healthy controls, we measured GFR as I-125-iothalamate clearance while simultaneously determining creatinine clearance.
Other Measurements: 24-hour urinary albumin excretion.
Results: In 121 patients with ADPKD (56% men; mean age, 40 +/- 11 [SD] years) and 215 controls (48% men; mean age, 53 +/- 10 years), measured GFR (mGFR) was 78 +/- 30 and 98 +/- 17 mL/min/1.73 m(2), respectively, and CCr(TS) was 15.9 +/- 10.8 and 10.9 +/- 10.6 mL/min/1.73 m(2), respectively (P <0.001). The higher CCr(TS) in patients with ADPKD remained significant after adjustment for covariates and appeared to be dependent on mGFR. Correlation and accuracy between mGFR and CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) estimated GFR (eGFR) were 0.95 and 99%, respectively; between mGFR and MDRD (Modification of Diet in Renal Disease) Study eGFR, they were 0.93 and 97%, respectively. Values for bias, precision, and accuracy were similar or slightly better than in controls. In addition, change in mGFR during 3 years of follow-up in 45 patients with ADPKD correlated well with change in eGFR.
Limitations: Cross-sectional, single center.
Conclusions: CCr(TS) in patients with ADPKD is higher than that in controls, but this effect is limited and observed at only high-normal mGFR. Consequently, the CKD-EPI and MDRD Study equations perform relatively well in estimating GFR and change in GFR in patients with ADPKD. (C) 2013 by the National Kidney Foundation, Inc.