Can estimated GFR be used in patients with rapidly changing kidney function?
GFR-estimating equation assumes that GFR is in steady state. In acute kidney injury, GFR is not in steady state, and the endogenous filtration markers serum creatinine and cystatin C will rise more slowly than the change in GFR.
In patients with rapidly changing kidney function, the rate and direction of change in the filtration marker reflects the magnitude and direction of the change in GFR.
• If the creatinine is increasing, the eGFR will overestimate the GFR.
• If the creatinine is decreasing, the eGFR will underestimate the GFR.
A kinetic equation for change in GFR was developed, which allows one to estimate the GFR by using the rate of change in eGFR and an assumed creatinine generation rate.