Salazar-Corcoran Equation (Obesity) Explained
Estimating creatinine clearance in obesity.
How the Salazar-Corcoran equation estimates creatinine clearance in obese patients.
Medically reviewed by Dr. Rishi Kumar Kafle, MBBS, MD, FASN. Last reviewed October 2026.
The Salazar-Corcoran equation estimates creatinine clearance in obese patients using both height and weight in its formula, rather than a single dosing weight. It addresses the overestimation that Cockcroft-Gault can produce when total body weight is used in obesity.
Why Obesity Breaks Cockcroft-Gault
Cockcroft-Gault scales clearance directly to body weight. In obesity, most excess weight is adipose tissue, which generates little creatinine, so plugging total body weight into the equation overstates clearance and can push a patient over a dosing threshold. The usual workaround is to substitute a corrected weight; Salazar-Corcoran takes a different route by building both height and weight into a single equation tuned to obese physiology.
| Approach | How it handles fat mass | Inputs |
|---|---|---|
| Cockcroft-Gault + total body weight | overestimates (counts all fat) | age, sex, TBW, Scr |
| Cockcroft-Gault + adjusted body weight | partially discounts fat (40%) | age, sex, IBW + 0.4×(TBW−IBW), Scr |
| Salazar-Corcoran | models height and weight together | age, sex, height, weight, Scr |
Salazar-Corcoran vs Adjusted Body Weight
The most common alternative is Cockcroft-Gault with adjusted body weight, which keeps the familiar 1976 equation but feeds it a weight corrected toward ideal. Both aim to avoid overestimating clearance in obesity; Salazar-Corcoran is a purpose-built equation, while adjusted body weight is a correction applied to a general one. See creatinine clearance in obesity and the ideal body weight calculator for the inputs behind the adjusted-weight method.
Total, Ideal, and Adjusted Body Weight
Clearance estimates in obesity depend on three body weights: total, ideal, and adjusted. Total body weight is the scale weight, including all adipose tissue. Ideal body weight is the weight predicted from height for a normal build, calculated by the Devine formula on the ideal body weight calculator. Adjusted body weight adds back a fraction, conventionally 40%, of the excess above ideal. The reasoning is that fat-free mass and metabolically active tissue rise somewhat with obesity, even though most excess weight is fat. Cockcroft-Gault with total body weight overstates clearance; with adjusted body weight it usually does not. In the standard rule, adjusted body weight replaces ideal body weight once actual weight is more than 130% of ideal (some hospitals use 120%). A 2012 comparison against measured creatinine clearance found it the least biased and most accurate weight in overweight, obese, and morbidly obese patients.
Salazar-Corcoran does not pick one weight. It incorporates both height and weight into a single equation derived in an obese population, so body composition is modelled within the formula rather than corrected beforehand. Both approaches aim at the same target: an estimate that does not over-credit fat mass with clearance it does not provide.
How to Read the Result
The output is a creatinine clearance in mL/min, read the same way as any Cockcroft-Gault value: against the dosing thresholds of the specific drug. Because most labels were validated on Cockcroft-Gault, many clinicians compute both (Salazar-Corcoran and Cockcroft-Gault with adjusted body weight) and reconcile them rather than relying on a single obesity-specific figure. When the two diverge widely, reconsider the weight assumptions rather than defaulting to the higher number.
Strengths and Limitations
The strength of Salazar-Corcoran is that it was designed specifically for obese patients and uses height to capture body composition more directly than a single weight term. Its limitations are that it is less validated and far less familiar than Cockcroft-Gault, most drug labels still reference Cockcroft-Gault values, and like every creatinine method it assumes a steady state. For rapidly changing function, the Jelliffe equation is the specialised tool to use instead. For staging rather than dosing, an eGFR from CKD-EPI 2021 is preferred: see CrCl vs eGFR.
A Practical Illustration
Consider a patient who is 160 cm tall but weighs 120 kg. Their ideal body weight is far lower than their scale weight, so almost all the excess is adipose tissue that contributes little creatinine. Feeding the full 120 kg into Cockcroft-Gault would inflate the estimated clearance and risk overdosing a renally-cleared drug. Using adjusted body weight pulls the figure back toward a physiological value, and Salazar-Corcoran reaches a similar goal by modelling height and weight together. With either method, do not use total body weight in a weight-scaled clearance equation in marked obesity.
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