Editing Liver function tests (section)

===Total bilirubin===
{{Main|Bilirubin}}
{| class="wikitable"
|+ Reference range in adults
! Parameters/units
! Total bilirubin
! Unconjugated bilirubin
! Conjugated bilirubin
|-
! mg/dL
| 0.1–1.0<ref name="Lisa B 2015"/> ||0.2–0.7<ref name="Lisa B 2015"/> || 0.1–0.4<ref name="Lisa B 2015">{{cite journal|last1=Lisa B|first1=VanWagner|title=Evaluating Elevated Bilirubin Levels in Asymptomatic Adults|journal=Journal of the American Medical Association|date=3 February 2015|volume=313|issue=5|pages=516–517|doi=10.1001/jama.2014.12835|pmid=25647209|pmc=4424929}}</ref>
|-
! μmol/L
| 2.0–21<ref name="Shivaraj 2009"/>
| < 12<ref name="Shivaraj 2009"/>
| < 8<ref name="Shivaraj 2009"/>
|}

Measurement of total [[bilirubin]] includes both unconjugated (indirect) and conjugated (direct) bilirubin. Unconjugated bilirubin is a breakdown product of [[heme]] (a part of [[hemoglobin]] in red blood cells). The liver is responsible for clearing the blood of unconjugated bilirubin, by 'conjugating' it (modified to make it water-soluble) through an enzyme named [[UDP-glucuronyl-transferase]]. When the total bilirubin level exceeds 17 μmol/L, it indicates liver disease. When total bilirubin levels exceed 40 μmol/L, bilirubin deposition at the sclera, skin, and mucous membranes will give these areas a yellow colour, thus it is called [[jaundice]].<ref name="Shivaraj 2009">{{cite journal|display-authors=3|last1=Shivaraj|first1=Gowda|last2=Prakash|first2=B Desai|last3=Vinayak|first3=V Hull|last4=Avinash|first4=AK Math|last5=Sonal N|first5=Venekar|last6=Shruthi S|first6=Kulkarni|title=A review on laboratory liver function tests|journal=The Pan African Medical Journal|date=22 November 2009|volume=3|issue=17|pages=17|pmid=21532726|pmc=2984286}}</ref>

The increase in predominantly unconjugated bilirubin is due to overproduction, reduced hepatic uptake of the unconjugated bilirubin and reduced conjugation of bilirubin. Overproduction can be due to the reabsorption of a [[haematoma]] and ineffective [[erythropoiesis]] leading to increased red blood cell destruction. [[Gilbert's syndrome]] and [[Crigler–Najjar syndrome]] have defects in the [[UDP-glucuronyl-transferase]] enzyme, affecting bilirubin conjugation.<ref name="Shivaraj 2009"/>

The degree of rise in conjugated bilirubin is directly proportional to the degree of hepatocyte injury. Viral [[hepatitis]] can also cause the rise in conjugated bilirubin. In parenchymal liver disease and incomplete extrahepatic obstruction, the rise in conjugated bilirubin is less than the complete [[common bile duct]] obstruction due to malignant causes. In [[Dubin–Johnson syndrome]], a mutation in [[Multidrug resistance-associated protein 2|multiple drug-resistance protein 2 (MRP2)]] causes a rise in conjugated bilirubin.<ref name="Shivaraj 2009"/>

In [[acute appendicitis]], total bilirubin can rise from 20.52 μmol/L to 143 μmol/L. In pregnant women, the total bilirubin level is low in all three trimesters.<ref name="Shivaraj 2009"/>

The measurement of bilirubin levels in the newborns is done through the use of bilimeter or transcutanoeus bilirubinometer instead of performing LFTs. When the total serum bilirubin increases over 95th percentile for age during the first week of life for high risk babies, it is known as hyperbilirubinemia of the newborn ([[neonatal jaundice]]) and requires [[light therapy]] to reduce the amount of bilirubin in the blood. Pathological jaundice in newborns should be suspected when the serum bilirubin level rises by more than 5&nbsp;mg/dL per day, serum bilirubin more than the physiological range, clinical jaundice more than 2 weeks, and conjugated bilirubin (dark urine staining clothes). [[Hemolytic disease of the newborn|Haemolytic jaundice]] is the commonest cause of pathological jaundice. Those babies with Rh hemolytic disease, ABO incompatibility with the mother, [[Glucose-6-phosphate dehydrogenase]] (G-6-PD) deficiency and minor blood group incompatibility are at increased risk of getting haemolytic jaundice.<ref>{{cite journal|last1=Sana|first1=Ullah|last2=Khaista|first2=Rahman|last3=Mehdi|first3=Hedayati|title=Hyperbilirubinemia in Neonates: Types, Causes, Clinical Examinations, Preventive Measures and Treatments: A Narrative Review Article|journal=Iranian Journal of Public Health|date=May 2016|volume=45|issue=5|pages=558–568|pmid=27398328|pmc=4935699}}</ref>