ESTIMATING RENAL FUNCTION


GFR in mL/min = (140 - age) x (ideal body wt in kg*) x (0.85 if patient is female)
72 x (serum Cr in mg/dl)

Ideal body weight estimation:

(Source: Cockcroft DW, Gault MH. Prediction of creatinine clearance from serum creatinine. Nephron. 1976;16:31-41.  Thanks to Christian Cable for correcting a previous error in my presentation of this formula)

Compared to this method and using a cutoff of 50mL/min for a diagnosis of "renal failure," serum Cr (using a cutoff of 1.7 mg/dL) had sensitivity of only 12.6% (though specificity of 99.9%) in a cohort of 854 pts > 65yo (Arch. Int. Med. 163:356, 2003--JW)

The following equation for estimating GFR was found to be more accurate than the Cockroft-Gault equation in one study (using GFR measured by renal clearance of 125-I-iothalamate as the gold standard) (Ann. Int. Med. 130:461, 1999)

In children, estimated GFR:

GFR (ml/min) = k x 1.73 x body length (cm) / serum [Cr] (mg/dl)

k = 0.55 for children or adol. girls; 0.7 for adol. boys

This method is more sens (95% vs 80%) & more specific (100% vs 75%) than serum[Cr] alone in determining renal insufficiency, but don't use in kids with acute RF, abnl body habitus, transplant pts, kids with elevated GFR or on TPN

(Ped.Clin.NA 34:571, 87; Am.J.Dis.Children, 146:1232, 10/92)