Creatinine is a non-protein waste product of creatine phosphate metabolism by skeletal muscle tissue. Creatinine production is continuous and is proportional to muscle mass. Serum creatinine concentrations are used in the determination of creatinine clearance (an indicator of GFR) and estimation of the GFR utilising the 4 variable MDRD equation. Each of these derived figures can then be used to both identify and monitor chronic kidney disease. Determination of urine creatinine is useful in:
Estimation of creatinine clearance requires a 24 hour urine sample and paired serum creatinine sample.
Male: 9.0-18.0 mmol/24hrs
Female: 7.0-16.0 mmol/24hrs