Figure 10.

Determinants of the serum level of endogenous filtration markers. The plasma level (P) of an endogenous filtration marker is determined by its generation (G) from cells and diet, extrarenal elimination (E) by gut and liver, and urinary excretion (UV) by the kidney. Urinary excretion is the sum of filtered load (GFR X P), tubular secretion (TS), and reabsorption (TR). In the steady state, urinary excretion equals generation and extrarenal elimination. By substitution and rearrangement, GFR can be expressed as the ratio of the non-GFR determinants (G, TS, TR, and E) to the plasma level. GFR, glomerular filtration rate. Reprinted with permission of American Society of Nephrology, Measured GFR as a confirmatory test for estimated GFR, Stevens LA, Levey AS.⁷⁹ J Am Soc Nephrol 20: 2305-2313, 2009; permission conveyed through Copyright Clearance Center, Inc.; accessed http://jasn.asnjournals.org/content/20/11/2305.full.pdf