Objective Glomerular filtration rate (GFR) is part of routine medical practice for clinical assessment of kidney function in health and disease conditions, and is determined by measuring the clearance of creatinine (Cl-Crn) or estimated (eGFR) from equations using serum creatinine (Crn) or cystatin C (Cyst C). Crn and Cyst C methods obviate the need for urine collection but their reliability under non-resting conditions is uncertain. This study compared GFR determined by Cl-Crn, Crn and Cyst C methods under the conditions of rest and after exercise.

Methods Twelve young male subjects performed a 30 min treadmill exercise at 80% of the maximal oxygen capacity. Venous blood samples and urine collections were collected before and after exercise and after recovery period. GFR rates were calculated from serum Crn and Cyst C equations, and Cl-Crn measured from serum and urine Crn output. Albumin was also determined for all samples.

Results Under resting conditions, eGFR from Crn and Cyst C did not differ from Cl-Crn (p=0.39). Immediately after exercise, GFR decreased significantly, regardless of the method, but more so for Cl-Crn (−30.0%; p<0.05) compared with Crn (−18.2%) and Cyst C (−19.8%). After the recovery period, GFR determined by Cl-Crn was returned to initial values whereas Crn and Cyst C remained reduced. Although eGFR methods accurately estimate GFR at rest, those methods underestimated the change in GFR after acute exercise.

Conclusions These results indicate that exercise-induced changes in GFR should be determined by Cl-Crn method.