The creatinine blood test is usually ordered along with a BUN (blood urea nitrogen) test to assess kidney function. Both are frequently ordered as part of a basic or comprehensive metabolic panel (BMP or CMP), groups of tests that are performed to evaluate the function of the body’s major organs. BMP or CMP tests are ordered on healthy people during routine physical exams and on acutely or chronically ill patients in the emergency room and/or hospital If the creatinine and BUN tests are found to be abnormal or if the patient has an underlying disease, such as diabetes, that is known to affect the kidneys, then these two tests may be used to monitor the progress of kidney dysfunction and the effectiveness of treatment. Blood creatinine and BUN tests may also be ordered to evaluate kidney function prior to some procedures, such as a CT (computed tomography) scan, that may require the use of drugs that can damage the kidneys.

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. Urine creatinine may also be used with a variety of other urine tests as a sort of correction factor. Since it is produced and removed at a relatively constant rate, the amount of urine creatinine can be compared to the amount of the other substance (such as protein) being measured.

Serum creatinine measurements (along with your age, weight, and gender) also are used to calculate the estimated glomerular filtration rate (EGFR), which is used as a screening test to look for evidence of kidney damage.

Creatinine may be ordered routinely as part of a comprehensive or basic metabolic panel, when someone has non-specific health complaints, is acutely ill, and/or when a doctor suspects kidney dysfunction. The creatinine blood test may be ordered, along with the BUN test, at regular intervals when the patient has a known kidney disorder or has a disease that may affect kidney function or be exacerbated by dysfunction. Both may be ordered when a CT scan is planned, prior to and during certain drug therapies, and before and after dialysis to monitor the effectiveness of treatments.

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

damage to or swelling of blood vessels in the kidneys (glomerulonephritis) caused by, for example, infection or autoimmune diseases;

bacterial infection of the kidneys (pyelonephritis);

death of cells in the kidneys’ small tubes (acute tubular necrosis) caused, for example, by drugs or toxins;

prostate disease, kidney stone, or other causes of urinary tract obstruction; or

reduced blood flow to the kidney due to shock, dehydration, congestive heart failure, atherosclerosis, or complications of diabetes.

Creatinine can also increase temporarily as a result of muscle injury.

Low levels of creatinine are not common and are not usually a cause for concern. They can be seen with conditions that result in decreased muscle mass.

Creatinine levels are generally slightly lower during pregnancy.

NOTE: The result of your creatinine test is measured by your doctor against a reference range for the test to determine whether the result is “normal” (it is within the range of numbers), high (it is above the high end of the range), or low (it is below the low end of the range). Because there can be many variables that affect the determination of the reference range, the reference range for this test is specific to the lab where your test sample is analyzed. For this reason, the lab is required to report your results with an accompanying reference range. Typically, your doctor will have sufficient familiarity with the lab and your medical history to interpret the results appropriately.

While there is no such thing as a “standard” reference range for creatinine, most labs will report a similar, though maybe not exactly the same, set of numbers as that included in medical textbooks or found elsewhere online. For this reason, we recommend that you talk with your doctor about your lab results. For general guidance only, we are providing the reference range for this test from the classic medical text, Tietz Textbook of Clinical Chemistry and Molecular Diagnostics.

For more information on reference ranges, please read Reference Ranges and What They Mean.

Drugs such as aminoglycosides (gentamicin) can cause kidney damage and so creatinine is monitored. Other drugs, such as cephalosprins (cefoxitin), may increase creatinine concentration without reflecting kidney damage.