Conjugated bilirubin-urine; Direct bilirubin-urine
This is a urine test that measures the amount of bilirubin.
Bilirubin metabolism begins with the breakdown of red blood cells (RBCs) by phagocytic cells (cells that consume and digest other cells). Hemoglobin is broken down to heme and globin. Heme is converted to bilirubin, which is then carried by albumin in the blood to the liver.
In the liver, most of the bilirubin is conjugated with glucuronic acid before it is excreted in the bile. Conjugated bilirubin is called direct bilirubin (DB), and unconjugated bilirubin is called indirect bilirubin (IB). Total bilirubin = DB + IB. Conjugated bilirubin is excreted into the bile by the liver and stored in the gall bladder or transferred directly to the small intestines.
Bilirubin is further metabolized by bacteria in the intestines to urobilins, which contribute to the color of the feces. A small percentage of these compounds are reabsorbed and eventually appear in the urine, where they are referred to as urobilinogen.
How the test is performed
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.
For an infant:
Thoroughly wash the area around the urethra (the hole from which the urine flows). Open a Urine collection bag (a plastic bag with an adhesive paper on one end), and place it on your 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. 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, as the bag is easily displaced. 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
This test may be performed when liver or gallbladder problems are suspected.
Bilirubin is not normally found in the urine.
What abnormal results mean
If the bile ducts are obstructed, direct bilirubin will build up to a high enough level that some of it will escape from the liver into the blood. If the levels are high enough, some of it will also appear in the urine. Only direct bilirubin appears in the urine. Increased direct bilirubin usually means that the biliary (liver secretion) ducts are obstructed.
Increased urinary bilirubin may indicate:
- biliary strictures
- gallstones in the biliary tract
- hepatitis with associated biliary obstruction
- surgical trauma affecting the biliary tract
- tumors of the liver or gall bladder
What the risks are
There are no risks.
Bilirubin can decompose in the presence of light.
Drugs than can falsely elevate the test result include allopurinol, some antibiotics, barbiturates, chlorpromazine, diuretics, ethoxazene, oral contraceptives, phenazopyridine, steroids, and sulfonamides.
Drugs that can cause false negative results include indomethacin and ascorbic acid.
by Brenda A. Kuper, M.D.
All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.