Creatinine Clearance (CrCl)

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Subject: Creatinine Clearance (CrCl)

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Definition

  • This test compares the creatinine in a 24-hour sample of urine to the creatinine level in the blood to show how much blood the kidneys are filtering out each minute. It is calculated by the formula:

    where UCr is urine creatinine, PCr is plasma creatinine

  • Normal range:

    • Male: 90–139 mL/minute

    • Female: 80–125 mL/minute

Use

  • Evaluate glomerular function

  • Monitor effectiveness of treatment in renal disease

Interpretation

  • Acromegaly

  • Acute tubular necrosis

  • Carnivorous diets

  • CHF

  • Dehydration

  • Diabetes

  • Exercise

  • Exposure to nephrotoxic drugs and chemicals

  • Gigantism

  • GN

  • Hypothyroidism

  • Infections

  • Neoplasms (bilateral renal)

  • Nephrosclerosis

  • Polycystic kidney disease

  • Pyelonephritis

  • Renal artery atherosclerosis and obstruction

  • Renal disease

  • Renal vein thrombosis

  • Shock and hypovolemia

  • TB

Decreased In

  • Acute or chronic GN

  • Anemia

  • Chronic bilateral pyelonephritis

  • Hyperthyroidism

  • Leukemia

  • Muscle wasting diseases

  • Paralysis

  • Polycystic kidney disease

  • Shock

  • Urinary tract obstruction (e.g., from calculi)

  • Vegetarian diets

Limitations

  • CrCl approximates GFR but overestimates it due to the fact that creatinine is secreted by the proximal tubule as well as filtered by the glomerulus.

  • Measurement of CrCl should be considered in circumstances when the estimating equation based on serum creatinine is suspected to be inaccurate or for patients with estimated GFR >60 mL/minute/1.73 m2 when a more accurate clearance measure is required for clinical decision making. Such circumstance may occur in people who are undergoing evaluation for kidney donation, treatment with drugs with significant toxicity that are excreted by the kidneys (e.g., high-dose methotrexate), or consideration for participation in research protocols.

  • Indications for a clearance measurement because estimates based on serum creatinine may be inaccurate because of extremes of age and body size, severe malnutrition or obesity, disease of skeletal muscle, paraplegia or quadriplegia, a vegetarian diet, rapidly changing kidney function, or pregnancy.

  • Drugs that may increase urine CrCl include enalapril, oral contraceptives, prednisone, and ramipril.

  • Drugs that may decrease the urine CrCl include acetylsalicylic acid, amphotericin B, carbenoxolone, chlorthalidone, cimetidine, cisplatin, cyclosporine, guancydine, ibuprofen, indomethacin, mitomycin, oxyphenbutazone, paromomycin, probenecid (coadministered with digoxin), and thiazides.

  • Excessive ketones in urine may cause falsely decreased values.

  • Failure to follow proper technique in collecting 24-hour specimen may invalidate test results.

  • Failure to refrigerate the specimen throughout the urine collection period allows decomposition of creatinine, causing falsely decreased values.

  • Consumption of large amounts of meat, excessive exercise, and stress should be avoided for 24 hours before the test.

Suggested Reading

National Kidney Foundation KDOQI Clinical Practice Guidelines for Chronic Kidney Disease: Evaluation, Classification, and Stratification. http://www.kidney.org/professionals/kdoqi/guidelines_ckd/p5_lab_g4.htm. Accessed November 18, 2010.
 
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