What is the role of a nicotinic acid test in the workup of Gilbert syndrome?

Updated: Sep 29, 2020
  • Author: Hisham Nazer, MBBCh, FRCP, DTM&H; Chief Editor: BS Anand, MD  more...
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Intravenous (IV) administration of 50 mg of nicotinic acid results in a 2- to 3-fold rise in plasma unconjugated hyperbilirubinemia within 3 hours. The mechanisms are multifactorial and probably related to the following:

  • Elevated osmotic fragility of red blood cells

  • Increase in splenic production of bilirubin

  • Transient inhibition of hepatic bilirubin-UGT activity

  • Increased splenic heme oxygenase activity

Because a similar, if less impressive, increase is observed in healthy individuals and those with hemolysis or liver disease, the nicotinic test, like the fasting test, does not clearly distinguish patients with Gilbert syndrome from those who are healthy or who have other disease processes.

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