How to interpret Cockcroft formula

The Cockcroft-Gault formula is used in clinical practice primarily to estimate creatinine clearance, which helps assess kidney function and guide drug dosing, especially for medications cleared renally.

It should be interpreted with caution because it estimates renal function based on serum creatinine, age, weight, and sex, but can be inaccurate in certain populations such as those with extremes of muscle mass (e.g., bodybuilders, amputees, or muscle wasting disorders), where it may overestimate or underestimate glomerular filtration rate (GFR).

In clinical practice, the Cockcroft-Gault formula is often used to adjust drug dosages in patients with renal impairment, with specific dose modifications recommended for various drugs depending on the estimated creatinine clearance.

However, for general assessment of kidney function, NICE guidelines recommend using the CKD-EPI creatinine equation to estimate GFR (eGFRcreatinine) as it is more accurate and standardised, with Cockcroft-Gault mainly reserved for drug dosing decisions.

Clinicians should also consider that eGFR values above 60 ml/min/1.73 m2 are less precise and that any significant changes in serum creatinine (>20%) may indicate a change in kidney function.

When highly accurate GFR measurement is required (e.g., chemotherapy dosing or donor evaluation), reference standard methods should be considered instead of formula-based estimates.