Creatinine clearance

Keywords: Cr clearance

Specimen:

Serum and timed urine collection for creatinine measurements; see Creatinine urine.

The patient should not eat meat at the meal immediately prior to, or during, the procedure.

Method:

A calculated value using serum and urine creatinine.

  1. Creatinine clearance (mL/min) = urine creatinine (mmol/L) x urine volume (mL) x 16.7 / plasma creatinine (mmol/L) x duration of collection (hours) The patient's height and weight may be measured so that surface area can be calculated and creatinine clearance adjusted to the 'standard' body surface area of 1.73m2 if required.

  2. Creatinine clearance may be estimated rather than measured -see Creatinine clearance Cockcroft and Gault.

Reference Interval:

Normal > 70 mL/min in a young adult. Typically falling approx 0.5 mL/min per year at ages over 30 years.

Application:

Creatinine clearance is a marker of glomerular filtration rate (GFR). Measured creatinine clearance is of particular use in patients with extremes of body size or composition where estimation formulae may be unreliable.

Interpretation:

Reduced creatinine clearance is an indicator of reduced glomerular filtration rate (GFR). This may indicate acute or chronic kidney disease. Doses of some drugs may need to be adjusted.

Complete and accurately timed urine collections are essential.

Reference:

Australian Medicines Handbook

Tietz Textbook of Clinical Biochemistry

Cockcroft DW and Gault MH. Nephron 1976 16: 31-41.