Creatinine Clearance Calculator

Serum creatinine sits in the denominator of the Cockcroft-Gault equation (CrCl = [(140-age) x weight x gender factor] / (72 x serum creatinine)), so it has an inverse relationship with the result: as the kidneys filter less waste and serum creatinine rises, the calculated clearance falls. Weight appears in the numerator and raises the calculated clearance when it increases, but age is different: it enters through (140 - age), so raising age LOWERS the calculated clearance -- the same direction as rising serum creatinine, not the same direction as rising weight.

The "Adjusted CrCl (1.73 m²)" output normalizes the Cockcroft-Gault result to a standard body surface area of 1.73 m², which requires estimating the patient's BSA. This calculator's BSA estimate assumes a fixed 170 cm reference height for every patient, because there is no height input on this calculator -- it does not use the patient's actual height. For patients close to 170 cm this is a reasonable approximation, but for patients much shorter or taller (small children, petite adults, very tall patients), the adjusted figure can be meaningfully inaccurate -- for a small, low-weight patient it can overstate the adjusted clearance by roughly 40-50%. Treat the adjusted output as a rough normalization rather than a personalized one, and rely on the unadjusted CrCl figure above when the patient's actual height differs substantially from 170 cm.

Cockcroft-Gault (1976) predates modern eGFR equations like CKD-EPI, but most drug product labels and renal dose-adjustment guidelines were validated against Cockcroft-Gault CrCl specifically, not eGFR. Many labels still specify CrCl cutoffs (for example, "reduce dose if CrCl < 30 mL/min") because that's the equation the original dosing studies used, so switching to eGFR for dosing decisions can produce a systematically different answer than what the label was validated against.

Not exactly. Creatinine clearance estimates how quickly the kidneys clear creatinine from the blood, but some creatinine is also actively secreted by the renal tubules in addition to being filtered, so creatinine clearance tends to run somewhat higher than true GFR, especially as kidney function declines. eGFR equations like CKD-EPI are considered closer estimates of true filtration rate, but Cockcroft-Gault remains the standard for many drug dosing decisions specifically.

The 0.85 correction factor accounts for the fact that women, on average, have lower muscle mass than men at the same body weight, and muscle mass is what generates creatinine in the first place. Without that adjustment, the equation would tend to overestimate creatinine clearance in female patients relative to their actual kidney function.