Creatinine - urine

Alternative names:

urine creatinine - spot collection

How the test is performed:

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 upon arising in the morning.
• Collect all subsequent urine (in a special container) for the next 24-hours.
• On day 2, urinate into the container in the morning upon arising.
• 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.

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 your infant. For males, the entire penis can be placed in the bag and the adhesive attached to the skin. For females, the bag is placed over the labia. Place a diaper over the infant (bag and all). The infant should be checked frequently and the bag changed after the infant has urinated into the bag. For active infants, this procedure may take a couple of attempts--lively infants can displace the bag, causing an inability to obtain the specimen. 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.

How to prepare for the test:

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.

How the test will feel:

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

Why the test is performed:

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

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

The creatine molecule gradually degrades to creatinine with time. 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 very little.

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