Measuring liver function

Last updated: Thursday, June 13, 2019

There is no single specific test that gives a measure of liver function, and assessments are made according to the whole clinical picture. This includes a combination of signs and symptoms, liver function tests, histopathology and imaging. Signs and symptoms include jaundice, pruritus, varices and spider naevi. Some of these are demonstrated below…

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Patients with more advanced liver dysfunction may have multiple symptoms and are more likely to have ascites, varices, and encephalopathy.

Liver Function Tests (LFTs) 

Not all LFTs are specific to the liver and they should be interpreted alongside other markers of liver dysfunction and the overall clinical picture.

  • Bilirubin – This is a product of haemoglobin breakdown and is normally excreted in the bile. It is particularly raised in cholestasis, but can also be raised in hepatocellular disease. 
  • Alkaline Phosphatase (ALP) – It is raised in cholestasis since it is secreted into bile ducts and slightly raised in hepatocellular disease. Other causes, such as bone diseases, can also increase ALP. 
  • Transaminases (ALT / AST) – These are markers of hepatocellular injury. Transaminases can also be raised in cardiac disease. 
  • Albumin – This is synthesised in the liver but has a long half-life (20 days). Although not a very specific indicator, a low albumin in association with deranged LFTs may suggest chronic liver disease and dysfunction. 
  • Prothrombin Time – As the liver makes clotting factors, an increased prothrombin time suggests the synthetic ability of the liver has been affected. Clotting factors have short half-lives, so changes in prothrombin time can happen quickly and can be seen in both acute and chronic liver disease. 

Local LFT reference ranges may differ and paediatric ranges may be different to those used for adults.

Interpreting Liver Function Tests (LFTs) 

When a change in a particular LFT becomes important is difficult to quantify, but any level greater than twice the upper limited of normal (ULN) could warrant further investigation. However, it is important to review this in line with the clinical picture – consider the patient as a whole, rather than looking at LFTs in isolation. Not all deranged LFTs indicate liver dysfunction.

Child-Pugh Score 

The Child-Pugh score, or its associated Child-Pugh grade, is used as a means to indicate the severity of the condition for patients with cirrhosis of the liver. It is occasionally used to adjust dosing by manufacturers, but is more useful as a measure of a patient’s degree of liver disease, rather than their liver function. Further information on the Child-Pugh score can be found on the Specialist Pharmacy Service website.