Kidney functional reserve and damage biomarkers in subclinical chronic kidney disease and acute kidney injury.

Significant loss of kidney function is not easily identified by serum creatinine (sCr)-based measurements. In the presence of normal sCr, decreased kidney functional reserve (KFR) may identify a significant loss of function. We evaluated KFR in experimental subclinical chronic kidney disease (sCKD) before and after brief ischemia-reperfusion injury (IRI). Using fluorescein isothiocyanate-labeled sinistrin, glomerular filtration rate (GFR) was measured transcutaneously before and after adenine-induced sCKD, and 1 and 2 wk after brief IRI, and compared with urinary kidney damage biomarkers. sCKD reduced stimulated and unstimulated GFR by ∼20% while reducing KFR by 50%. IRI reduced unstimulated GFR for 14 days, but KFR remained relatively unchanged in sCKD and transiently increased in control kidneys at 7 days. sCr increased and creatinine clearance (CrCl) decreased only immediately after IRI; sCr and CrCl correlated poorly with measured GFR except on