H–20
IDEXX VetTest* Chemistry Analyzer Operator’s Manual
Total bilirubin/TBIL
Hemoglobin from degenerate erythrocytes is converted to bilirubin in the
reticuloendothelial system. Free unconjugated bilirubin is transported to the liver
bound to albumin where it is conjugated with glucuronic acid and eliminated in the
bile. In obstructive liver disease, the concentration of conjugated bilirubin in the blood
increases.
During intravascular hemolysis, very large numbers of erythrocytes are destroyed
quickly and the conjugation mechanism in the liver becomes overloaded so that high
concentrations of free bilirubin are found in the blood. If the loss of hemoglobin and
erythrocytes is very large, anoxia may occur. Hepatocyte dysfunction follows leading
to cellular swelling which occludes the bile canaliculi so preventing the elimination of
conjugated bilirubin. A concomitant rise in conjugated bilirubin then occurs.
Principal reason for performing the test:
To detect obstructive liver disease.
Note: In the healthy dog and cat the concentration of total bilirubin in the serum is
very low. Visual inspection of the sample will frequently indicate whether bilirubin
determination is necessary.
Most common abnormality indicated by the test:
Intrahepatic obstruction
Special precautions in sample collection:
Blood samples taken for bilirubin determination should be processed, centrifuged, and
analyzed immediately as bilirubin degrades rapidly in light. If immediate analysis is
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a refrigerator. Sample must be allowed to come to room temperature before analysis.
It is critical that samples be properly centrifuged. Otherwise, leukocytes and platelets
may remain in suspension, even when red cells have been separated. Cellular material
on the slide may cause significant positive error.
Limitations of procedure:
Samples that come in contact with alcohol from sterile wipes may become hemolyzed,
which will increase the results.
Complementary tests:
Total bilirubin should be determined with other tests of hepatic function and damage.
Hematocrit should also be performed to eliminate or confirm the presence of hemolytic
disease. Determination of urinary urobilinogen and bilirubin may also be useful.
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