Bilirubin

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Latest Edit: Hector 2014-03-24 (EDT)

See Also Lab Tests

Bilirubin is the product of the breakdown of hemoglobin from red blood cells by reticuloendothelial cells of the spleen and bone marrow. Following it's production, bilirubin is transported to the liver where it is made water soluble and excreted via the gallbladder in the bile. Therefore increased serum levels of bilirubin indicate either excessive red blood cell destruction or a problem in the liver that may be inhibiting the normal excretion of bilirubin. Testing for bilirubin is done to screen for or monitor liver disorders or hemolytic anemia.[1],[2]

Discussion

  • Total bilirubin is the only value reported on a standard chemistry screen.
  • If levels are high, a differentiation of the total bilirubin will give you the conjugated and unconjugated values.
  • Direct and indirect values on routine chemistry screens can assist in determining whether the cause of an increased total biliruin is due to pre-hepatic situations, such as increased hemolysis, or post-hepatic problems such as biliary obstruction.

1. Indirect or unconjugated bilirubin: refers to the fat-soluble form of bilirubin that is formed during the initial chemical breakdown of hemoglobin and, while being transported in the blood, is mostly bound to albumin.

2. Direct or conjugated bilirubin: refers to a water-soluble form of bilirubin formed in the liver by the chemical addition of sugar molecules to unconjugated bilirubin; when present in the blood, conjugated bilirubin can become chemically bound to albumin.

Patient Preparation

  • Fasting requirements vary among different laboratories
  • Factors which can cause increased levels
  • prolonged fasting
  • Drugs: allupurinol, anabolic steroids, antibiotics, antimalarials, ascorbic acid, azathioprine, chlorpropamide (Diabinese), cholinergics, codeine, dextran, diuretics, epinephrine, meperidine, methotrexate, methyldopa, monamine oxidase inhibitors, morphine, nicotinic acid (large doses), oral contraceptives, phenothiazines, quinidine, rifampin, salicylates, steroids, sulfonamides, theophylline, and vitamin A
  • Factors which can cause decreased levels
  • Exposure of sample to sunlight or bright artificial light at room temperature, high fat meal
  • Drugs: barbiturates, caffeine, penicillin, and salicylates (high dose)

Clinical Implications

Ranges: The following are the reference ranges for this lab. However, lab ranges can vary by laboratory and country. [2]

Standard U.S. Units Standard International Units
Conventional Laboratory Range 0.1-1.2 mg/dL 1.7-20.5 umol/L
Optimal Range 0.1-1.2 mg/dL 1.7-20.5 umol/L
Alarm Ranges > 2.6 mg/dL > 44.5 umol/L


High levels indicate

Low levels indicate

  • Spleen insufficiency

Associated Tests

References

  1. Pagana Kathleen D, Pagana Timothy J, (1998) Mosby's Manual of Diagnostic and Laboratory Tests, Mosby, Inc
  2. 2.0 2.1 Weatherby Dicken, Ferguson Scott (2002) Blood Chemistry and CBC Analysis: Clinical Laboratory Testing from a Functional Perspective, Bear Mountain Cite error: Invalid <ref> tag; name "weatherby" defined multiple times with different content