To Estimate Total and Direct Bilirubin
in Serum^24
24.1 Theory
Bilirubin originates from breakdown of heme. It is a waste product and the body
eliminates it through bile. The heme present in erythrocytes contributes approxi-
mately 85% of total bilirubin which is destroyed in the reticuloendothelial cells. The
destruction of red blood cell precursors in the bone marrow and catabolism of other
heme-containing proteins like myoglobin, cytochromes, and peroxidases release the
remaining 15% of bilirubin. Biliverdin isfirst formed from the porphyrin part of
heme in reticuloendothelial cells and is reduced to bilirubin called unconjugated
bilirubin, which is then transported to the liver in association with albumin. This
unconjugated bilirubin is insoluble in water. Bilirubin then enters to microsomes of
hepatocytes and conjugated by the action of glucuronyl transferase to produce
bilirubin monoglucuronide and diglucuronide (conjugated bilirubin). The bilirubin
conjugated with glucuronic acid is water soluble and it exerted through bile. The
conjugated bilirubin present in bile passes along the bile ducts into the intestine.
Here it is reduced by bacterial action and is also deconjugated, mainly in the colon to
“urobilinogens.”Urobilinogen is recycled through the body and a part of it is
excreted through the urine (Fig.24.1).
24.2 Specimen Requirements
Serum is a desirable sample. Protect the sample from light since exposure to white or
UV light may decrease total and indirect bilirubin up to 20%. Hemolysis increases
indirect bilirubin.
#Springer Nature Singapore Pte Ltd. 2018
V. Kumar, K. D. Gill,Basic Concepts in Clinical Biochemistry: A Practical Guide,
https://doi.org/10.1007/978-981-10-8186-6_24
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