The creatinine urine test measures the amount of creatinine in urine.

Spot collection: obtain a sample of urine by urinating and saving part of the urine in a container.

A 24-hour urine sample is needed. The health care provider will instruct you, if necessary, to discontinue drugs that may interfere with the test.

• On day 1, urinate into the toilet when you get up in the morning.
• Afterwards, collect all urine in a special container for the next 24 hours.
• On day 2, urinate into the container when you get up in the morning.
• Cap the container. Keep it in the refrigerator or a cool place during the collection period. Label the container with your name, the date, the time of completion, and return it as instructed.

For an infant:

Thoroughly wash the area around the urethra. Open a urine collection bag (a plastic bag with an adhesive paper on one end), and place it on the infant. For boys, the entire penis can be placed in the bag and the adhesive attached to the skin. For girls the bag is placed over the labia. Diaper as usual over the secured bag.

This procedure may take a couple of attempts -- lively infants can displace the bag. The infant should be checked frequently and the bag changed after the infant has urinated into the bag. The urine is drained into the container for transport to the laboratory.

Deliver it to the laboratory or your health care provider as soon as possible upon completion.

No special preparation is necessary for this test, but if the collection is being taken from an infant, a couple of extra collection bags may be necessary.

The test involves only normal urination, and there is no discomfort.

A measurement of the serum creatinine level is used to evaluate kidney function. Urine creatinine levels can be used as a screening test to evaluate kidney function, or as part of the creatinine clearance test.

Creatinine is a breakdown product of creatine, which is an important part of muscle. By far, the most important source of energy inside cells is the ATP molecule, with its high-energy phosphate bonds.

When one of these bonds is broken, energy is released, and ATP becomes ADP. Creatine phosphate represents a backup energy source for ATP because it can quickly re-convert ADP back to ATP.

Over time, the creatine molecule gradually degrades to creatinine. Creatinine is a waste product, that is, it cannot be used by cells for any constructive purpose. The daily production of creatine, and subsequently creatinine, depends on muscle mass, which fluctuates little in most normal people over long periods of time.

Creatinine is excreted from the body entirely by the kidneys. With normal kidney function, the serum (blood) creatinine level should remain constant and normal.