Estimating the glomerular filtration rate. Dos and don'ts for assessing kidney function.

The National Kidney Foundation's guidelines for CKD make the following recommendations about assessment of kidney function. Estimates of GFR are the best overall indices of the level of kidney function. The level of GFR should be estimated from prediction equations that take into account the serum creatinine concentration and some or all of the following variables: age, gender, race, and body size. In adults, the MDRD study and Cockcroft-Gault equations provide useful estimates of GFR. In children, the Schwartz and Counahan-Barratt equations are useful. The serum creatinine concentration should not be used alone to assess the level of kidney function. Clinical laboratories should report an estimate of GFR using a prediction equation, in addition to reporting the creatinine measurements. Autoanalyzer manufacturers and clinical laboratories should calibrate serum creatinine assays using an international standard. Measurement of creatinine clearance using timed (e.g., 24-hour) urine collections does not improve the estimate of GFR over that provided by prediction equations. A 24-hour urine sample provides useful information for estimation of GFR in individuals with exceptional dietary intake (vegetarian diet, use of creatine supplements) or muscle mass (amputation, malnutrition, muscle wasting). It is also useful for assessment of diet and nutritional status and need to start dialysis.