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Alternative Names Return to topTotal bilirubin; Unconjugated bilirubin; Indirect bilirubin; Conjugated bilirubin; Direct bilirubin
Definition Return to top
Bilirubin is a product that results from the breakdown of hemoglobin. Total and direct bilirubin are usually measured to screen for or to monitor liver or gallbladder problems.
How the Test is Performed Return to top
A blood sample is needed. For information on how this is done, see: Venipuncture .
The laboratory specialist spins the blood in a machine called a centrifuge, which separates the liquid part of the blood (serum) from the cells. The bilirubin test is done on the serum.
How to Prepare for the Test Return to top
You should not eat or drink for at least 4 hours before the test. Your health care provider may instruct you to stop taking drugs that affect the test.
Drugs that can increase bilirubin measurements include allopurinol, anabolic steroids, some antibiotics, antimalaria medications, azathioprine, chlorpropamide, cholinergics, codeine, diuretics, epinephrine, meperidine, methotrexate, methyldopa, MAO inhibitors, morphine, nicotinic acid, birth control pills, phenothiazines, quinidine, rifampin, steroids, sulfonamides, and theophylline.
Drugs that can decrease bilirubin measurements include barbiturates, caffeine, penicillin, and high-dose salicylates such as aspirin.
Why the Test is Performed Return to top
This test is useful in determining if a patient has liver disease or a blocked bile duct.
Bilirubin metabolism begins with the breakdown of red blood cells in many parts of the body. Red blood cells contain hemoglobin, which 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 chemically attached to another molecule before it is released in the bile. This "conjugated" (attached) bilirubin is called direct bilirubin; unconjugated bilirubin is called indirect bilirubin. Total serum bilirubin equals direct bilirubin plus indirect bilirubin.
Conjugated bilirubin is released into the bile by the liver and stored in the gallbladder, or transferred directly to the small intestines. Bilirubin is further broken down by bacteria in the intestines, and those breakdown products contribute to the color of the feces. A small percentage of these breakdown compounds are taken in again by the body, and eventually appear in the urine.
Normal Results Return to top
Note: mg/dL = milligrams per deciliter
Normal values may vary slightly from laboratory to laboratory.
What Abnormal Results Mean Return to top
Jaundice is a yellowing of the skin and the white part of the eye, which occurs when bilirubin builds up in the blood at a level greater than approximately 2.5 mg/dL. Jaundice occurs because red blood cells are being broken down too fast for the liver to process. This might happen due to liver disease or bile duct blockage.
If the bile ducts are blocked, direct bilirubin will build up, escape from the liver, and end up in the blood. If the levels are high enough, some of it will 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 indirect or total bilirubin may be a sign of:
Increased direct bilirubin may indicate:
Additional conditions under which the test may be performed:
Considerations Return to top
Factors that interfere with bilirubin testing are:
References Return to top
Berk PD, Korenblat KM. Approach to the patient with jaundice or abnormal liver test results. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 150.Update Date: 2/23/2009 Updated by: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.