Wang K, Zelnick LR, Chen Y, et al. - Considering that proximal tubular secretory clearance may be decreased in autosomal dominant polycystic kidney disease (ADPKD) prior to detectable alterations in GFR, researchers analyzed blood and urine samples from 31 ADPKD cases with preserved GFR (mean eGFR = 111 ± 11 ml/min per 1.73 m²) and 25 healthy controls as well as from 95 ADPKD cases with decreased GFR (mean eGFR = 53 ± 21 ml/min per 1.73 m²) and 92 people with non-ADPKD CKD, to quantify secretory solutes using targeted mass spectrometry. They found that tubular secretory solute excretion was lower in patients with ADPKD and preserved and reduced GFR vs healthy controls and patients with non-ADPKD CKD. In ADPKD, impaired tubular secretion was indicated independent of GFR.