What is Creatinine
Test Description:
Creatinine is the waste product of creatine phosphate, a compound found in the
skeletal muscle tissue. It is excreted entirely by the kidneys. The creatinine level is
affected primarily by renal dysfunction and is thus very useful in evaluating renal
function. Increased levels of creatinine indicate a slowing of the glomerular filtration
rate. Since creatinine levels normally remain constant, even with aging, this test is
particularly useful in evaluating renal dysfunction in which a large number of
nephrons have been destroyed. The creatinine level is usually determined in conjunction
with the blood urea nitrogen (BUN) in assessing renal function. The normal
ratio of BUN to creatinine ranges from 6:1 to 20:1. Testing of the creatinine
level in the blood is also used to monitor patients on drugs known to be nephrotoxic,
such as aminoglycosides.
Normal Values
Female: 0.6–1.2 mg/dL (53–106 μmol/L SI units)
Male: 0.8–1.4 mg/dL (70–123 μmol/L SI units)
Children: 0.2–1.0 mg/dL (18–88 μmol/L SI units)
Possible Meanings of Abnormal Values
Increased Decreased
Congestive heart failure Atrophy of muscle tissue
Dehydration Pregnancy
Diabetes mellitus
Glomerulonephritis
Gout
Hyperthyroidism
Multiple myeloma
Nephritis
Pyelonephritis
Renal failure
Rheumatoid arthritis
Shock
Subacute bacterial endocarditis
Systemic lupus erythematosus
Uremia
Urinary obstruction
Contributing Factors to Abnormal Values
• Creatinine levels are 20% to 40% higher in the late afternoon than in the morning.
• Test results may be altered by hemolysis of the blood sample and by ingestion of a
high meat diet.
• Drugs which may increase creatinine levels: amphotericin B, androgens, arginine,
ascorbic acid, barbiturates, captopril, cephalosporins, chlorthalidone, cimetidine,clofibrate, clonidine, corticosteroids, dextran, disopyramide, doxycycline, fructose,
gentamicin, glucose, hydralazine, hydroxyurea, kanamycin, levodopa, lithium,
mannitol, meclofenamate, methicillin, methyldopa, metoprolol, minoxidil, nitrofurantoin,
propranolol, protein, pyruvate, sulfonamides, streptokinase, testosterone,
triamterene, trimethoprim.
• Drugs which may decrease creatinine levels: cefoxitin, cimetidine, chlorpromazine,
marijuana, thiazide diuretics, vancomycin.
Interventions/Implications
Pretest
• Explain to the patient the purpose of the test and the need for a blood sample to be
drawn.
• No fasting is required before the test.
Procedure
• A 7-mL blood sample is drawn in a red-top collection tube.
• Gloves are worn throughout the procedure.
Posttest
• Apply pressure at venipuncture site. Apply dressing, periodically assessing for continued
bleeding.
• Label the specimen and transport it to the laboratory.
• Report abnormal findings to the primary care provider.
Clinical Alerts
• Both BUN and creatinine should be assessed prior to administration of any
nephrotoxic drug.
• Monitor creatinine at baseline and at least every 12 months for patients taking
metformin for diabetes mellitus Type 2. The drug can accumulate and potentially
cause lactic acidosis in patients with renal insufficiency.
Creatinine Clearance
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