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Creatinine - urine

Definition

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

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 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.

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 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.

Normal Values

Normal values are highly dependent on the age and lean body mass of the person the urine is being collected from. Normal value ranges may vary slightly among different laboratories. Urine creatine (24-hour sample) values may therefore be quite variable and can range from 500 mg/day to 2000 mg/day.

What abnormal results mean

Abnormal results of urine creatinine and creatinine clearance are often non-specific, but may include the following conditions:

Additional conditions under which the test may be performed:

What the risks are

There are essentially no risks.

Special considerations

Drugs that can increase creatinine measurements include: aminoglycosides (gentamicin), cimetidine, heavy metal chemotherapeutic agents (Cisplatin), and nephrotoxic drugs, such as cephalosporins (cefoxitin).

Illustrations

Female urinary tract
Female urinary tract
Male urinary tract
Male urinary tract
Creatinine tests
Creatinine tests
Creatinine urine test
Creatinine urine test

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Urine creatinine - spot collection