Creatinine Clearance Calculator

Creatinine is the spontaneous breakdown product of creatine and phosphocreatine in muscle, generated at a rate that is nearly constant for a given person because roughly 1 to 2 percent of the muscle creatine pool converts each day. It is freely filtered at the glomerulus and barely reabsorbed, which makes its clearance a usable stand-in for glomerular filtration rate. The Cockcroft-Gault equation exploits the fact that muscle mass, and therefore creatinine production, tracks with body weight and declines with age: the numerator (140 minus age) multiplied by weight estimates daily production, and dividing by 72 times the serum creatinine converts it to millilitres per minute. The 0.85 factor for women reflects lower average muscle mass per kilogram. The result is a whole-body clearance in mL/min, not indexed to body surface area, which is why pharmacists prefer it for drug dosing: most renal dose-adjustment thresholds, such as the 30 and 50 mL/min cut-offs on many labels, were derived using this equation. Estimated GFR from CKD-EPI is standardized to 1.73 square metres and is used instead for chronic kidney disease staging, where KDIGO defines G1 at 90 or above, G2 at 60 to 89, G3a at 45 to 59, G3b at 30 to 44, G4 at 15 to 29, and G5 below 15, sustained for at least three months. Both equations fail in the same situations: unstable creatinine during acute kidney injury, extremes of muscle mass such as amputation, cirrhosis, or bodybuilding, and drugs including trimethoprim, cimetidine, and cobicistat that block tubular secretion and raise creatinine without changing true filtration. Cockcroft-Gault also overestimates in obesity when total rather than adjusted body weight is used.

Creatinine became measurable in 1886, when Max Jaffe described the orange-red complex formed between creatinine and alkaline picrate, a colorimetric reaction that carried clinical chemistry for the next century despite interference from glucose, ketones, and bilirubin. Poul Brandt Rehberg introduced the clearance concept for creatinine in 1926, and Homer Smith's work at New York University in the 1930s and 1940s established inulin clearance as the reference standard for glomerular filtration, since inulin is filtered and neither secreted nor reabsorbed. Timed 24-hour urine collections remained the practical clinical method, but they were slow and frequently mis-collected. Donald Cockcroft and Henry Gault published their prediction equation in the journal Nephron in 1976, fitting measured creatinine clearances from a few hundred hospitalized adults, almost all men, to age, weight, and serum creatinine so that clearance could be estimated without a urine collection. Two later developments changed the landscape. Laboratories moved to enzymatic assays traceable to isotope dilution mass spectrometry, which report lower creatinine values than the old Jaffe method and therefore shift Cockcroft-Gault results upward. Andrew Levey and colleagues then produced the MDRD equation in 1999 from the Modification of Diet in Renal Disease study and the more accurate CKD-EPI equation in 2009; in 2021, following a joint National Kidney Foundation and American Society of Nephrology task force, Lesley Inker and co-authors published a refitted CKD-EPI equation in the New England Journal of Medicine that removed the race coefficient entirely.