Filtration Markers in Acute Kidney Injury

Effect of an acute glomerular filtration rate (GFR) decline on generation, filtration, excretion, balance, and serum level of endogenous filtration markers. After an acute GFR decline (first panel), generation of the marker is unchanged, but filtration and excretion are reduced, resulting in retention of the marker (the nonshaded area in the second panel), a rising positive balance (the shaded area in the third panel) and a rising plasma level until a new steady state is reached (bottom panel). During the non–steady state, estimated GFR (eGFR) would be lower than measured GFR. Although GFR remains reduced, the rise in plasma level leads to an increase in filtered load (the product of GFR times the plasma level) until filtration equals generation. At that time, cumulative balance and the plasma level plateau at a new steady state. In the new steady state, eGFR would approximate measured GFR. GFR is expressed in units of milliliter per minute per 1.73 m². Tubular secretion and reabsorption and extrarenal elimination are assumed to be zero.