Direct Bilirubin

0-0.3 mg/dl

• Bilirubin is a breakdown product of haemoglobin. Normally when blood cells become old they are trapped and destroyed by the spleen. When this occurs , the haemoglobin must be broken down in the liver to bilirubin in order to be disposed off. Bilirubin is eventually excreted in the bile and leaves the body in the faeces . 
• Bilirubin is the main bile pigment in humans, which when increased causes the yellow discolouration of skin and eyes called Jaundice . Bilirubin is taken from the blood, processed ( conjugated to make it water soluble ) by the liver , and then excreted into bile by the liver . 
• Serum Bilurubin is generally considered as a true test of LFT , since it reflects the livers true ability to take up, process and secrete Bilirubin into the bile. 

Two forms of Bilirubin are:

1. Direct Bilirubin ( Conjugated Bilirubin) 
2. Indirect Bilirubin ( UnConjugated Bilirubin) 

Total Bilirubin = Indirect Bilirubin + Direct Bilirubin

• Bilirubin production and ecxretion follows a specific pathway . When the reticulo endothelial system breaks down old red blood cells, bilirubin is one of the waste products . This free bilirubin is in a lipid soluble form that must be made water soluble to be excreted.
• The free or unconjugated bilirubin is carried by albumin to the liver , where it is converted or conjugated and made water soluble .Once it is conjugated into a water soluble form , bilirubin can be excreted in the urine .
• An enzyme glucuronyl transferase , is necessary for the conjugation of Bilirubin . Either a lack of this enzyme or the presence of drugs that interfere with it impairs the livers ability to conjugate bilirubin . 
• The term Direct and Indirect reflect the way the two types of bilirubin react to certain dyes. Conjugated bilirubin is water soluble and reacts directly when dyes are added to the blood specimen. The non soluble , free bilirubin does not react to the reagents until alcohol is added to the solution , thus the measurement of this type of bilirubin is indirect .
• Both Direct and Indirect Bilirubin is elevated in Hepatitis
• Inflammation restricted to biliary tract or its obstruction results in elevation predominantly of direct bilirubin

• When there is s/s of jaundice, have anaemia ,have h/o heavy drinking , have cirrhosis.
• When there are symptoms like weakness , fatigue , nausea , vomiting , dark urine , light coloured stools , pruritus, diarrhoea

Adults 

• Hepatocellular disease
• Biliary tract obstruction
• Drug induced Cholestasis
• Prolonged Total Parenteral Nutrition 

Neonatal patients 

• Sepsis
• Intra uterine viral infections 
• Neonatal hepatitis
• Intrahepatic & Extra hepatic biliary atresia 
• Biliary tract obstruction - Choledochal cyst , Abdominal mass , Annular pancreas
• Trisomy 18
• Galactosemia
• Tyrosinemia
• Dubin johnsons , 
• Rotors Syndromes
• Hypermethioninemia
• Alpha 1 antitrypsin deficiency
• Hypopituitarism
• Hypothyroidism