Creatinine - serum

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Creatinine tests

Creatinine - serum

Definition:

Creatinine is a breakdown product of creatine, which is an important part of muscle. A serum creatinine test measures the amount of creatinine in the blood.

Alternative Names:

Serum creatinine

How the test is performed:

Adult or child:
Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic. An elastic band is placed around the upper arm to apply pressure and cause the vein to swell with blood.

A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

Infant or young child:
The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. A bandage may be applied to the puncture site if there is any bleeding.

How to prepare for the test:

The health care provider may advise you to discontinue drugs that may affect the test (see special considerations).

Infants and children:
The preparation you can provide for this test depends on your child's age, previous experiences, and level of trust. For general information regarding how you can prepare your child, see the following topics:

Infant test or procedure preparation (birth to 1 year)
Toddler test or procedure preparation (1 to 3 years)
Preschooler test or procedure preparation (3 to 6 years)
Schoolage test or procedure preparation (6 to 12 years)
Adolescent test or procedure preparation (12 to 18 years)

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 performed to evaluate kidney function. If kidney function is abnormal, creatinine levels will increase in the blood, due to decreased excretion of creatinine in the urine. Creatinine levels also vary according to a person's size and muscle mass.

Normal Values:

A normal (usual) value is 0.8 to 1.4 mg/dl. Normal value ranges may vary slightly among different laboratories.

Females have a lower creatinine than males, due to less muscle mass.

Note: mg/dl = milligrams per deciliter

What abnormal results mean:

For abnormal results, the following applies:

Greater-than-normal levels may indicate:

Acute tubular necrosis
Dehydration
Diabetic nephropathy
Eclampsia (a condition of pregnancy that includes seizures)
Glomerulonephritis
Muscular dystrophy
Pre-eclampsia (pregnancy-induced hypertension)
Pyelonephritis
Reduced renal blood flow (shock, congestive heart failure)
Renal 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:

Acute nephritic syndrome
Alport syndrome
Atheroembolic renal disease
Chronic renal failure
Complicated UTI (pyelonephritis)
Cushing's syndrome
Dementia due to metabolic causes
Dermatomyositis
Digitalis toxicity
Ectopic Cushing's syndrome
End-stage renal disease
Epilepsy
Generalized tonic-clonic seizure
Goodpasture's syndrome
Hemolytic-uremic syndrome (HUS)
Hepatorenal syndrome
IgM mesangial proliferative glomerulonephritis
Interstitial nephritis
Lupus nephritis
Malignant hypertension (arteriolar nephrosclerosis)
Medullary cystic disease
Membranoproliferative GN I
Membranoproliferative GN II
Noninsulin-dependent diabetes mellitus (NIDDM)
Polymyositis (adult)
Prerenal azotemia
Primary amyloid
Rapidly progressive (crescentic) glomerulonephritis
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

Why is the test performed:
A measurement of the serum creatinine level is used to evaluate kidney function.

Creatinine is a breakdown product of creatine, which is an important component of muscle. Creatinine can be converted to the ATP molecule, which is a high-energy source. The daily production of creatine and subsequently creatinine, depends on muscle mass, which fluctuates very little.

Creatinine is excreted from the body entirely by the kidneys. With normal renal excretory function, the serum creatinine level should remain constant and normal.

Special considerations:

Drugs that can increase creatinine measurements include aminoglycosides (for example, gentamicin), Bactrim, cimetidine, heavy metal chemotherapeutic agents (for example, Cisplatin), and nephrotoxic drugs -- such as cephalosporins (for example, cefoxitin).

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