Creatinine test — Overview covers definition, preparation, results of this common blood test.
A creatinine test is a measure of how well your kidneys are performing their job of filtering waste from your blood.
Creatinine is a chemical compound left over from energy-producing processes in your muscles. Healthy kidneys filter creatinine out of the blood. Creatinine exits your body as a waste product in urine.
A measurement of creatinine in your blood or urine provides clues to help your doctor determine how well the kidneys are working.
Your doctor or other health care provider may order a creatinine test for the following reasons:
A standard blood test is used to measure creatinine levels in your blood (serum creatinine). Your doctor may ask you not to eat (fast) overnight before the test.
For a creatinine urine test, you may need to collect urine over 24 hours in containers provided by the clinic.
For either test, you may need to avoid eating meat for a certain period before the test. If you take a creatine supplement, you'll likely need to stop use.
For a serum creatinine test, a member of your health care team takes a blood sample by inserting a needle into a vein in your arm.
For a urine test, you’ll need to provide a single sample in the clinic or collect samples at home over 24 hours and return them to the clinic.
Results from creatinine in blood or urine are measured and interpreted in many ways, including the following:
Creatinine usually enters your bloodstream and is filtered from the bloodstream at a generally constant rate. The amount of creatinine in your blood should be relatively stable. An increased level of creatinine may be a sign of poor kidney function.
Serum creatinine is reported as milligrams of creatinine to a deciliter of blood (mg/dL) or micromoles of creatinine to a liter of blood (micromoles/L). The typical range for serum creatinine is:
The measure of serum creatinine may also be used to estimate how quickly the kidneys filter blood (glomerular filtration rate). Because of variability in serum creatinine from one person to another, the GFR may provide a more accurate reading on kidney function.
The formula for calculating GFR takes into account the serum creatinine count and other factors, such as age and sex. A GFR score below 60 suggests kidney disease. The range of scores below 60 may be used to monitor treatment and disease progression.
Creatinine clearance is a measure of how well the kidneys filter creatinine out of the bloodstream for excretion in urine.
Creatinine clearance is usually determined from a measurement of creatinine in a 24-hour urine sample and from a serum sample taken during the same time period. However, shorter time periods for urine samples may be used. Accurate timing and collection of the urine sample is important.
Creatinine clearance is reported as milliliters of creatinine per minute per body surface area (mL/min/BSA). The typical range for men, 19 to 75 years old, is 77 to 160 mL/min/BSA.
The typical range, by age, for creatinine clearance in women is as follows:
Standard measures have not been determined for older adults.
Results lower than the typical range for your age group may be a sign of poor kidney function or conditions that affect blood flow to your kidneys.
Another interpretation of urine creatinine count is called the albumin/creatinine ratio. Albumin is a protein in blood. Healthy kidneys generally don't filter it out of the blood, so there should be little to no albumin found in the urine.
Albumin/creatinine ratio describes how much albumin is in a urine sample relative to how much creatinine there is. The results are reported as the number of milligrams (mg) of albumin for every gram (g) of creatinine. Results indicating a healthy kidney are:
A higher than typical result may be a sign of kidney disease. In particular, the result may indicate a complication of diabetes called diabetic nephropathy, or diabetic kidney disease.
Your doctor or other health care provider will discuss the results of a creatinine test with you and help you understand what the information means for a diagnosis or treatment plan.