Tubular Secretion of Creatinine in Autosomal Dominant Polycystic Kidney Disease: Consequences for Cross-sectional and Longitudinal Performance of Kidney Function Estimating Equations

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 125 I-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 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.