Bilirubin

Test Description
Bilirubin, which is one of the components of bile, is formed in the liver, spleen, and
bone marrow. It is also formed as a result of hemoglobin breakdown, as in the destruction
of red blood cells. There are three types of bilirubin: total, direct (conjugated),
and indirect (unconjugated). Total bilirubin is composed of the direct bilirubin plus
the indirect bilirubin. The total bilirubin level increases with any type of jaundice.
Normally, direct or conjugated, bilirubin is excreted by the gastrointestinal (GI)
tract, with only minimal amounts entering the bloodstream. It was originally named
“direct” bilirubin because this water-soluble type of bilirubin reacts directly with the
reagents added to the blood sample. Its level rises in the blood when obstructive
jaundice (as from gallstones) or hepatic jaundice occurs, because the bilirubin is
unable to reach the intestines for excretion and instead, enter the bloodstream for
excretion by the kidneys. Direct bilirubin is the only type of bilirubin able to cross the
glomerular filter; thus it is the only type of bilirubin that can be found in the urine.
Indirect bilirubin, also known as free or unconjugated bilirubin, is normally
found in the bloodstream. Its name comes from the fact that this non-water-soluble
bilirubin does not directly react with reagents added to a blood sample. Alcohol
must be added for the reaction to occur. Indirect bilirubin rises in cases of
hemolytic jaundice, in which the breakdown of hemoglobin results in a higher than
normal level of indirect bilirubin being present in the bloodstream. This is the type
of bilirubin elevated in cases of hepatocellular dysfunction, such as hepatitis.
Typically, only the total bilirubin is reported. If the total bilirubin is abnormal,
further testing is done to differentiate the level of direct and indirect bilirubin.
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THE EVIDENCE FOR PRACTICE

Initial evaluations should determine whether the elevated serum bilirubin is conjugated
(direct) or unconjugated (indirect). Asymptomatic adult patients with an isolated, mild
unconjugated hyperbilirubinemia should be evaluated for Gilbert’s syndrome, hemolysis,
and medication-induced hyperbilirubinemia. If conjugated hyperbilirubinemia is present,
the presence of concomitant alkaline phosphatase elevations must be assessed and biliary
obstruction should be excluded
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Normal Values                                     

Total bilirubin:                                             0.3–1.0 mg/dL (5–17 μmol/L SI units)
Direct (conjugated) bilirubin:                      0.0–0.4 mg/dL (0–7 μmol/L SI units)
Indirect (unconjugated) bilirubin:                0.1–1.0 mg/dL (1–17 μmol/L SI units)
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Possible Meanings of Abnormal Values

Increased Direct (Conjugated) Bilirubin

Biliary obstruction
Cancer of the head of the pancreas
Choledocholithiasis
Cirrhosis
Dubin-Johnson syndrome
Hepatitis
Obstructive jaundice
Pregnancy

Increased Indirect (Unconjugated) Bilirubin

Autoimmune hemolysis
Cirrhosis
Crigler-Najjer syndrome
Erythroblastosis fetalis
Gilbert’s syndrome
Hemolytic transfusion reaction
Hepatitis
Malaria
Myocardial infarction
Pernicious anemia
Septicemia
Sickle cell disease
Tissue hemorrhage
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Contributing Factors to Abnormal Values

• Hemolysis of the blood sample will alter test results.
• Exposure of the blood sample to sunlight or artificial light for 1 hour or more will
 decrease the bilirubin content of the sample.
• Testing with contrast media within 24 hours will alter test results.
• Drugs that may increase total bilirubin: allopurinal, anabolic steroids, antimalarials,
   ascorbic acid, azathioprine, chlorpropamide, cholinergics, codeine, dextran, diuretics,
   epinephrine, isoproterenol, levodopa, MAO inhibitors, meperidine, methyldopa,
    methotrexate, morphine, oral contraceptives, phenazopyridine, phenothiazines,
    quinidine, rifampin, streptomycin, theophylline, tyrosine, vitamin A.
• Drugs that may decrease total bilirubin: barbiturates, caffeine, chlorine, citrate, corticosteroids,
 ethanol, penicillin, protein, salicylates, sulfonamides, urea.
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Interventions/Implications

Pretest

• Explain to the patient the purpose of the test and the need for a blood sample to be drawn.
• Fasting for 4 to 8 hours is required before the test. Water is permitted.

Procedure

• A 7-mL blood sample is drawn in a lavender-top collection tube.
• Gloves are worn throughout the procedure.

Posttest

• Apply pressure at venipuncture site. Apply dressing, periodically assessing for continued
 bleeding.
• Protect the specimen from bright light by wrapping the sample tube in foil or placing in
a refrigerator.
• Label the specimen and transport it to the laboratory.
• Report abnormal findings to the primary care provider.