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 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