Pathological Analysis Department Title of the lecture: The estimation of Msc . Tholfikar Ahmed Tholfikar-Ahmed @mustaqbal-college.edu.iq

CLINICAL BIOCHEMISTRY The estimation of Bilirubin

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Pathological Analysis Department Title of the lecture: The estimation of Bilirubin Msc . Tholfikar Ahmed Tholfikar-Ahmed @mustaqbal-college.edu.iq

Bilirubin

Bilirubin is the yellow breakdown product of normal catabolism. Heme is found in hemoglobin, a principal component of red blood cells.

Bilirubin is excreted in bile and urine, and elevated levels may indicate certain diseases. It is responsible for the yellow color of bruises, yellow color of urine via its reduced breakdown product, .

Bilirubin can be "conjugated" with a molecule of which makes it soluble in water.

Metabolism

1- Unconjugated (indirect)

Red blood cells generated in the bone marrow are disposed of in the spleen when they get old or damaged. This releases hemoglobin, which is broken down to heme as the globin parts are turned into amino acids. The heme is then turned into unconjugated bilirubin in the monocyte macrophages system of the spleen. This unconjugated bilirubin is not soluble in water, due to intramolecular hydrogen bonding. It is then bound to albumin and sent to the liver.

2- Conjugated (direct)

In the liver, bilirubin is conjugated with glucuronic acid by the enzyme glucuronyltransferase, making it soluble in water: the conjugated version is also often called "direct" bilirubin. Much of it goes into the bile and thus out into the small intestine. Though most bile acid is resorbed in the terminal ileum to participate in enterohepatic circulation, conjugated bilirubin is not absorbed and instead passes into the colon.

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Pathological Analysis Department Title of the lecture: The estimation of Bilirubin Msc . Tholfikar Ahmed Tholfikar-Ahmed @mustaqbal-college.edu.iq

Formation of urobilins in the intestine

Bilirubin diglucuronide is hydrolyzed and reduced by bacteria in the gut to yield a colorless compound. Most of the urobilinogen is oxidized by intestinal bacteria to which gives feces the characteristic brown color. The remainder of the urobilinogen is transported by the blood to the kidney where is converted to yellow urobilin and excreted giving urine its characteristic color.

Blood levels

The bilirubin level found in the body reflects the balance between production and excretion .

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Pathological Analysis Department Title of the lecture: The estimation of Bilirubin Msc . Tholfikar Ahmed Tholfikar-Ahmed @mustaqbal-college.edu.iq

Normal serum bilirubin level range from 0.2 to 0.8 mg/dL . The unconjugated bilirubin from 0.2 to 0.6 mg /dL and conjugated bilirubin 0.0 to 0.2 mg/dL .

Hyperbilirubinemia

Hyperbilirubinemia results from a higher-than-normal level of bilirubin in the blood. Mild rises in bilirubin may be caused by:

 Hemolysis or increased breakdown of red blood cells

 Gilbert's syndrome – a genetic disorder of bilirubin metabolism that can result in mild .

 Rotor syndrome: no itching jaundice, with rise of bilirubin in the patient's serum, mainly of the conjugated type

Very high levels of bilirubin may be caused by:

 Neonatal hyperbilirubinaemia, where the newborn's liver is not able to properly process the bilirubin causing jaundice

 Unusually large bile duct obstruction, e.g. stone in common bile duct, tumour obstructing common bile duct etc.

 Severe liver failure with cirrhosis (e.g. primary biliary cirrhosis)

 Choledocholithiasis (chronic or acute).

Jaundice

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Pathological Analysis Department Title of the lecture: The estimation of Bilirubin Msc . Tholfikar Ahmed Tholfikar-Ahmed @mustaqbal-college.edu.iq

Yellow color of skin sclera and nail caused by deposition of bilirubin secondary to increased bilirubin in blood, causes:-

- Infection by hepatitis B virus is transmitted through serum .the virus is highly contagious and can be destroyed only by boiling for 20 minutes it is a DNA virus , which destroys the hepatic cells . - Hepatocellular jaundice is the infection with hepatitis viruses it may be due to hepatitis A virus which is transmitted by the intake of contaminated food and water .

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