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

How the test is performed

Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.

Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.

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, cefoxitin)
• 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 evaluate kidney function. 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 value is 0.8 to 1.4 mg/dL.

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

Note: Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

What abnormal results mean

Higher-than-normal levels may indicate:

• 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 indicate:

• Muscular dystrophy (late stage)
• Myasthenia gravis

Additional conditions under which the test may be performed:

• Alport syndrome
• 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
• Primary amyloidosis
• Secondary systemic amyloid
• Thrombotic thrombocytopenic purpura
• Wilms' tumor

What the risks are

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

References

Bazari H. Approach to the patient with renal disease. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 115.