Creatinine Clearance

Clearance of endogenous creatinine is the most practical test of renal function. Decreased renal blood flow results in decreased clearance. Urine is collected for 24 hours and a blood sample is collected during this collection interval. Serum and urine creatinine levels are measured and the creatinine clearance calculated using the following formula:

Urine creatinine x urine volume/Serum creatinine x minutes of duration = mL/minute

This value is then corrected for body surface area:

Creatinine Clearance =mL/minute x1.73 m2/Patient's surface area (m2)

The accuracy of the creatinine clearance calculation depends on the accuracy of the urine collection. Twenty four-hour urine collections are considered optimal because they account for diurnal variation in creatinine clearance. The laboratory has added “grams of creatinine per 24 hours” to the creatinine clearance report. This calculation is valuable in determining if a 24-hour urine collection is complete. Creatinine values <1g/24 hours for men or <0.9g/24 hours for women nearly always mean that the urine collection was incomplete. Normal urine volume is 0.6 to 2.0 liters per day, but most people produce between 1.0 and 1.5 liters per day.

Creatinine excretion increases with muscle mass, is lower among women and decreases with age. Nomograms are available to determine a patients age adjusted creatinine clearance percentile rank. Men usually excrete 19 to 26 mg of creatinine per kg of body weight daily and women usually excrete 14 to 21 mg/kg body weight. The normal range is 1 –2 g per 24 hours for men and 0.6 – 1.5 g per 24 hours for women. Avoidance of exercise and adequate hydration are important factors in ensuring accurate results.

Renal failure causes reduced creatinine clearance. Creatinine clearance values of 30 to 40 mL/min/1.73 m2 suggest moderate renal impairment, while values <28 suggest severe impairment.

Creatinine clearance may not be accurate in the following medical conditions.

Over Estimated

Under Estimated


Body building

Muscle wasting

Anabolic steroids


High protein diet

Vegetarian diet

Congestive heart failure




Reference range is 60‑180 mL/min/1.73M2

Specimen requirement is a twenty‑four hour urine collection in a container without preservative. Instruct the patient to void in the morning and discard the specimen. All urine is then collected for the next 24 hours, including the next first morning void. The container should be refrigerated during and after the collection. Patient's height and weight are needed for calculating the clearance. One SST tube of blood is also required for measurement of serum creatinine.

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