Creatinine - blood

Definition

Creatinine is a breakdown product of creatine, which is an important part of muscle. This article discusses the laboratory test to measure the amount of creatinine in the blood.

Creatinine can also be measured with a urine test. See: Creatinine - urine

Alternative Names

Serum creatinine

How the test is performed

A blood sample is needed. For information on how this is done, see: Venipuncture

How to prepare for the test

The health care provider may tell you to stop taking certain drugs that may affect the test. Such drugs include:

• Aminoglycosides (for example, gentamicin)
• Cimetidine
• Heavy metal chemotherapy drugs (for example, cisplatin)
• Kidney damaging drugs such as cephalosporins (for example, cephalexin)
• Nonsteroidal anti-inflammatory drugs (NSAIDs)
• Trimethoprim

How the test will feel

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the test is performed

The test is done to see how well your kidneys work. Creatinine is removed from the body entirely by the kidneys. If kidney function is abnormal, creatinine levels will increase in the blood (because less creatinine is released through your urine).

Creatinine levels also vary according to a person's size and muscle mass.

Normal Values

A normal result is 0.7 to 1.3 mg/dL for men and 0.6 to 1.1 mg/dL for women.

Females usually have a lower creatinine than males, because they usually have less muscle mass.

The examples above are common measurements for results of these tests. Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your doctor about the meaning of your specific test results.

What abnormal results mean

Higher than normal levels may be due to:

• Acute tubular necrosis
• Dehydration
• Diabetic nephropathy
• Eclampsia (a condition of pregnancy that includes seizures)
• Glomerulonephritis
• Kidney failure
• Muscular dystrophy
• Preeclampsia (pregnancy-induced hypertension)
• Pyelonephritis
• Reduced kidney blood flow (shock, congestive heart failure)
• Rhabdomyolysis
• Urinary tract obstruction

Lower than normal levels may be due to:

• Muscular dystrophy (late stage)
• Myasthenia gravis

Additional conditions under which the test may be performed:

• Alport syndrome
• Amyloidosis
• Atheroembolic kidney disease
• Chronic kidney disease
• Cushing syndrome
• Dementia due to metabolic causes
• Dermatomyositis
• Diabetes
• Digitalis toxicity
• Ectopic Cushing syndrome
• Generalized tonic-clonic seizure
• Goodpasture syndrome
• Hemolytic-uremic syndrome (HUS)
• Hepatorenal syndrome
• Interstitial nephritis
• Lupus nephritis
• Malignant hypertension (arteriolar nephrosclerosis)
• Medullary cystic kidney disease
• Membranoproliferative GN I and GN II
• Type 2 diabetes
• Polymyositis (adult)
• Prerenal azotemia
• Thrombotic thrombocytopenic purpura
• Wilms' tumor

What the risks are

There is very little risk involved with having your blood taken. Veins and arteries vary in size from one patient to another and from one side of the body to the other. Taking blood from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight but may include:

• Excessive bleeding
• Fainting or feeling light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

Special considerations

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References

Landry DW, Bazari H. Approach to the patient with renal disease. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 116.