1. The GFR is the generally accepted, best index of kidney function. CKD is defined as a GFR less than 60 mL/min per 1.73 m 2 , as well as markers of kidney damage. In the United States the most common marker of kidney damage is urine albumin. The level of GFR is associated with metabolic complications of CKD, risk of death, risk of progression of CKD, and cardiovascular disease.
2. Normal GFR varies according to age, sex, and body size; in young adults, it is approximately 120 to 130 mL/min per 1.73 m 2 and declines with age.
3. The most common method used to assess GFR is serum creatinine combined with an estimating equation. The equation includes other variables, such as age, sex, race, and body size, as surrogates for non-GFR determinants of creatinine. The CKD-EPI equation is currently the most accurate way to estimate GFR from serum creatinine.
4. The two important limitations of serum creatinine are its generation from muscle mass and its presence in diet. Cystatin C is an alternative filtration marker that appears not to be generated by muscle mass. The CKD-EPI creatinine-cystatin 2012 equation provides the most precise estimate of GFR.
5. Online calculators are available that easily allow eGFR to be computed.
6. KDIGO recommends that eGFRcr be used as an initial test with confirmatory tests used if eGFRcr is suspected to be inaccurate or for important clinical decisions.
7. For patients with rapidly changing kidney function, the estimated GFR is inaccurate. The equation depends on a stable creatinine. If the creatinine is increasing, the eGFR will overestimate the GFR. In contrast, if the creatinine is decreasing, the eGFR will underestimate the true GFR.
Glomerular filtration rate (GFR) assesses kidney function. GFR is measured by renal clearance techniques; inulin clearance is the gold standard but is not easily measured.
Thus, other methods to determine GFR have been utilized. Endogenous creatinine clearance (CrCl) is the most widely used, but creatinine secretion falsely elevates GFR.
Cimetidine inhibits creatinine secretion, such that CrCl equals GFR, provided there are no difficulties with bladder emptying.
Estimation of GFR from serum creatinine (e.g. Schwartz formula) is useful clinically; however, such formulae have not been updated for enzymatic creatinine autoanalyzers.
