Liver function tests

Before we move on to consider the details of the transplantation procedure and all the different medical professionals involved, we need to consider how doctors can actually tell if someone’s liver is failing.

Interestingly, many of those key liver functions we described in Step 1.6 are important here as they underpin some of the biochemical tests that are performed if a doctor suspects a patient has a sick liver. There are many different kids of liver disease (which we will introduce briefly in the next step) so there are also many different blood tests and diagnostic tools that a Hepatologist may perform. However there are several key, commonly used tests which can give you a really good indication that something is wrong with a liver, these can be divided into several categories : 1) Tests for liver synthetic function or cellular damage 2) Tests for a specific disease 3) Tests relating to the appearance of the liver

We will consider these individually below.

1) Testing liver function and damage – here a doctor may use biochemical tests on samples of blood to determine if the liver is working properly. Classical examples of this kind of test include

TRANSAMINASES – these are enzymes which reside within hepatocytes and help carry out chemical reactions during cellular metabolism. You wouldn’t normally expect to see them in the blood. If you find levels of aspartate aminotransferase (AST) or alanine aminotransferase (ALT) elevated in the blood, this indicates hepatocyte damage.

ALKALINE PHOSPHATASE – this is another enzyme, but is localised to biliary cells within the liver. Elevated levels of this in blood indicate biliary damage.

BILIRUBIN – this is a very important test of liver function. Elevated blood levels indicate that either liver cells have been injured or that there is an obstruction to bile flow or inherited disorder in bilirubin metabolism

ALBUMIN – you’ll remember that albumin is made by hepatocytes so reduced levels in serum is a good indication that the synthetic capacity of the liver is impaired.

PROTHROMBIN TIME – this is another test of the liver’s synthetic function, here detecting the time it takes for a sample of blood to clot. If it takes too long, then this suggests that secretion of clotting factors by the liver may be impaired.

2) Tests for a specific disease – whilst all the tests above tell you that ‘something’ is wrong with the liver they are less useful at identifying the precise cause of a disease. Often a patient’s history may help if they report excessive alcohol consumption, exposure to hepatotoxins or are perhaps at risk of obesity-related disease. There are some specific tests for the presence of Hepatitis B and C infection however. Also some diseases may be caused by an inherited change in a particular gene. A good example is a disease called haemachromatosis, which involves some of the iron transport molecules. So for some diseases a genetic screen can help with diagnosis.

3) Testing the appearance of the liver – often the best tool for diagnosis is to look at the liver itself. There are non-invasive screens such as MRI scans and elastography that can tell you if a liver is fatty or scarred by cirrhosis. In some cases however the most informative test to diagnose or stage a disease is to look at a small sample of tissue, or ‘biopsy’ under the microscope. This is a risky procedure but incredibly informative. We’ll learn more about a situation when this is very valuable from our discussion with Professor Hubscher next week.

In the meantime, we’ve added some useful links for more information below and don’t forget to share anything useful you discover yourself with your fellow students in the discussion below.