To diagnose kidney malfunction if the eGFR (estimate of glomerular filtration rate) is unsuitable
If your doctor thinks that you may have a problem affecting the function of your kidneys, such as an obstruction within the kidney, acute or chronic kidney failure, dehydration, shock, or another disease, such as congestive heart failure. The most common test for kidney function is serum creatinine and the eGFR, however in some patients further testing is required.
Both a urine sample (24-hour collection) and a blood sample drawn from a vein in your arm
This test measures the concentration of creatinine in both a sample of blood and a sample of urine from a 24-hour urine collection. The results are used to calculate the amount of creatinine that has been cleared from the blood and passed into the urine over a 24 hour time period.
Creatinine is a chemical derived from creatine, a nitrogen-containing organic compound used by muscles to store and transfer energy. The amount of creatinine produced in the body is dependent on muscle mass and is constant for an individual. It is removed from the body as blood passes through the kidneys. By measuring creatinine in the blood and in the urine, it is possible to determine the amount of blood filtered by the kidneys in a measured period of time. A calculation is made based on the amount of creatinine in the urine, the time period of collection, and the amount of creatinine in the blood serum or plasma. The results are a measure of kidney function.
Since the amount of creatinine produced depends upon muscle mass, in some circumstances, e.g. in children, the calculation will need to be corrected for body surface area.
The test requires a 24-hour urine collection and a blood sample drawn either at the beginning or end of the urine collection. The blood sample is drawn by needle from a vein in the arm.
The creatinine urine test is used to help evaluate the rate and efficiency of kidney filtration. It is used to help detect kidney dysfunction resulting from either kidney disease or decreased blood flow to the kidneys.
Creatinine is normally filtered through the glomerulus - a group of blood vessels in the kidneys responsible for filtration. An abnormal kidney function test indicates that the person may have lost more than 30-40 per cent of their kidney's function, which may be a permanent or temporary loss.
The test may be requested if you suffer from kidney disease or a condition known to effect kidney function such as congestive heart failure, shock, or diabetes. It may also be requested to assess kidney function prior to the administration of some toxic drugs as dose may be dependent on kidney function.
A decreased creatinine clearance may indicate a decrease in the amount of blood filtered by the kidney due to disease within the kidney cells or to decreased delivery of blood to the kidneys. Congestive heart failure, dehydration, shock, obstruction within the kidney, or acute or chronic kidney failure are among the possible causes.
Certain drugs, such as aminoglycosides, cimetidine, cisplatin, and cephalosporins can decrease the creatinine clearance measurement. Diuretics can increase the result.
Creatinine clearance may also be measured before you are prescribed certain drugs which rely on good kidney function in order to allow them to be removed from the body effectively after they have carried out their purpose. Other straightforward methods of estimating the function of your kidneys now in routine use across Australia include the calculation of estimated glomerular function rate (eGFR) from a single blood sample taken from a vein in your arm.
Creatinine, glomerular filtration rate (eGFR)
Conditions: Congestive heart failure, kidney disease
RCPA Manual: Creatinine urine
RCPA Manual: Creatinine clearance
Kidney Health Australia
Medical News Today: What to know about urine tests for creatinine
Mayo Clinic: Creatinine test
Last Review Date: April 1, 2020