Creatinine - serum
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.
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)
- School age 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.
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
- Diabetic nephropathy
- Eclampsia (a condition of pregnancy that includes seizures)
- Muscular Dystrophy
- Pre-eclampsia (pregnancy-induced hypertension)
- Reduced renal blood flow (shock, congestive heart failure)
- Renal failure
- 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
- Digitalis toxicity
- Ectopic Cushing’s syndrome
- End-stage renal disease
- 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.
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).
by Martin A. Harms, M.D.
All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.