## 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:

- For men: 50kg + 2.3 kg/inch over 5ft
- For women: 45.5kg + 2.3kg/inch over 5 ft

(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)

- GFR = 170 x [age in years to the -.176 power] x [0.762 if
pt is female] x [1.180 if pt is black] x [serum urea nitrogen in mg/dL to
the -0.170 power] x [serum albumin concentration in g/dL to the 0.318
power]/[serum creatinine in mg/dL]

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)