Blood Tests
Bilirubin is broken down by light. Tubes containing blood or (especially) serum to be used in bilirubin assays should be protected from illumination.
Bilirubin (in blood) is in one of two forms:
| Abb. | Name(s) | Water-soluble? | Reaction |
| "BC" | "Conjugated" or "Direct bilirubin" |
Yes (bound to glucuronic acid) | Reacts quickly when dyes (diazo reagent) are added to the blood specimen to produce azobilirubin "Direct bilirubin" |
| "BU" | "Unconjugated" or "Indirect bilirubin" | No | Reacts more slowly. Still produces azobilirubin. Ethanol makes all bilirubin react promptly then calc: Indirect bilirubin = Total bilirubin – Direct bilirubin |
Total bilirubin ("TBIL") measures both BU and BC. Total and direct bilirubin levels can be measured from the blood, but indirect bilirubin is calculated from the total and direct bilirubin.
Indirect bilirubin is fat-soluble and direct bilirubin is water-soluble.
Read more about this topic: Bilirubin
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