Creatinine Test

The creatinine test is used to measure the amount of creatinine in the blood. Because creatinine is a nonprotein end product of creatine phosphate, which is used in skeletal muscle contraction, the daily production of creatine, and the following product, creatinine, depends on muscle mass, which fluctuates very little. Creatine is an important compound produced by the body and it combines with phosphorus to make a high-energy phosphate compound in the body. Creatine phosphate is used in skeletal muscle contraction.

Since creatinine is excreted entirely by the kidneys, it is directly related to renal function. When the kidneys are functioning normally, the serum creatinine level should remain constant and normal. Slight increases in creatine levels can appear after meals, especially after ingestion of large quantities of meat, and some diurnal variation may occur. Serious renal disorders, such as glomerulonephritis, pyelonephritis, and urinary obstruction, will cause abnormal elevations.

The creatinine level is interpreted in conjunction with another kidney function test called the Blood Urea Nitrogen (BUN). Although the serum creatinine level has much the same significance as the BUN, it still tends to rise later and because of this, determinations of creatinine help to chronicle a disease process. Generally, a doubling of creatinine suggests a 50% reduction in kidney filtration rate.

Why is it Used?

It is used to determine whether your kidneys are functioning normally because in this case the amount of creatinine in your blood will be very low. This test is used to diagnose impaired kidney function and to determine renal damage.

How and When is it Used?

A combination of blood and urine creatinine levels may be used to calculate a "creatinine clearance." This measures how effectively your kidneys are filtering small molecules like creatinine out of your blood.

Creatinine may be part of a basic metabolic panel, widely used when someone has non-specific health complaints, or it may be ordered if your doctor suspects kidney problems. The test is also used to monitor treatment of kidney disease or to monitor kidney function while you are on certain drugs.

Preparing for the test

The creatinine test requires a blood sample and it is recommended that the patient should fast for at least eight hours before the test. The physician may also require that ascorbic acid (vitamin C), barbiturates, and diuretics be withheld for 24 hours.

Risks and Precautions:

Although the risks for this test are minimal, it may include slight bleeding from the blood-drawing site, fainting or feeling lightheaded after venipuncture, or hematoma—blood accumulating under the puncture site.

A diet high in meat content can cause transient elevations of serum creatinine. Some drugs that may increase creatinine values include gentamicin, cimetidine, heavy-metal chemotherapeutic agents, and other drugs toxic to the kidneys, such as the cephalosporins.

Test Results

Normal results

Normal values can vary from laboratory to laboratory, but are generally in the following ranges:

• Adult female: 0.5-1.1 mg/dL
• Adult male: 0.6-1.2 mg/dL
• Adolescent: 0.5-1.0 mg/dL
• Child: 0.3-0.7 mg/dL
• Infant: 0.2-0.4 mg/dL
• Newborn: 0.3-1.2 mg/dL.

Abnormal results

2 to 4 mg/dL indicate the presence of impairment of renal function. Greater than 4 mg/dL indicates serious impairment in renal function.

What does these results mean?

Increased creatinine levels in the blood suggest diseases that affect kidney function. These can include:

• Glomerulonephritis (swelling of the kidney’s blood vessels);
• Pyelonephritis (pus-forming infection of the kidneys);
• Acute tubular necrosis (death of cells in the kidneys’ small tubes);
• Urinary tract obstruction; or
• Reduced blood flow to the kidney due to shock, dehydration, congestive heart failure, atherosclerosis, or complications of diabetes.

What else is to be known?

Since creatinine levels are in proportion to muscle mass, women tend to have lower levels than men. In general, creatinine levels will stay the same if one consumes a normal diet. However, eating large amounts of meat may cause short-lived increases in blood creatinine levels. Taking creatine supplements may also increase creatinine.

There are very few drugs that interfere with the creatinine test, although there are some drugs that can cause some impairment in kidney function. Creatinine levels may be monitored if a patient is taking one of these drugs.