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LFTs – Liver Function Tests

Liver function test tubes

Introduction

Almost every patient admitted to hospital will have their liver function tested, along with a full blood count, urea and electrolytes and glucose. Liver function tests (LFTs) are also one of the most commonly requested tests in primary care.

Interpreting liver function tests can be a tricky concept to understand. For starters, the term “liver function tests” is actually somewhat of a misnomer, and several authorities now recommend the term “liver blood tests” as an alternative. This is because only some of the tests included in a normal set of liver blood tests are actually tests of liver function. They are mainly indicators of liver damage or liver fibrosis. Tests that indicate the true synthetic function of the liver are not typically included in a standard set of “LFTs”.

A typical set of LFTs will include:

We can consider liver blood tests as being subdivided into three categories

When LFT’s are routinely measured (e.g. in primary care as a screening tool), an abnormality is found in 3.5% of people. 0.3% of patients have ALT levels 2x that of normal. Abnormal LFTs are unlikely to resolve spontaneously – and as such there is little benefit to simply repeating tests that are raised, without other investigation or management.
The majority of patients with abnormal test results have significant liver disease.
The two most common liver diseases are alcoholic liver disease, and non alcoholic fatty liver disease (NAFLD).
Normal LFT’s do not necessarily exclude the possibility of chronic liver disease.

In the case of raised liver blood tests, a liver screen is often performed to help identify the cause. Usually this includes:

ALT

Alanine transaminase – aminotransferase – 5-45 U/L

AST

Aspartate transaminase  – 5-45 U/L

ALP

Alkaline phosphatase  – 25-110 U/L

Gamma-GT 

GGT – <65 U/L

Bilirubin

1-20 µmol/l
Most commonly used to asses for obstructive jaundiceLevels also likely to be raised in liver damage and in cases of severe RBC damage. Test for urobilinogen can be useful in determining whether it is due to RBC’s or a problem with the liver / bile system.

Albumin

33-49g/l
This is the major protein constituent of plasma, and accounts for over 50% of all plasma proteins. It is manufactured in the liver from ingested amno-acids. It helps to regulate osmotic pressure as well as transport nutrients and waste products.
It may often be reduced as a result of;

Patterns of L​FT results

There are four main patterns of liver function test results, and these help identify what the cause of the abnormal results are. In reality, often there is a mixed picture, making interpretation much more difficult!

  1. Obstructive aka Cholestatic Pattern – due to bile duct obstruction. Remember this could be any part of the ducts, even the tiny ones, within the liver itself, it doesn’t necessarily mean the common bile duct. This pattern will give:
    1. High bilirubin
    2. High ALP
    3. Normal ALT (or only slightly raised in comparison to ALP)
  2. Hepatitic Pattern – this is a sign of acute liver inflammation. The pattern will give:
    1. Very high ALT – between 200- 2000 U/L
    2. Varying bilirubin – the higher the level, the greater the degree of damage
    3. Slightly raised ALP – should be no higher than 2x normal.
    4. Increased prothrombin time – usually will be slightly raised. In cases of severe liver failure it may exceed 25 seconds
  3. Synthetic failure – an emergency presentation requiring urgent referral for ultrasound +/- urgent admission to hospital
    1. Jaundice (high bilirubin)
    2. Increased INR
    3. Low platelets
    4. Low Albumin
  4. Isolated raised Bilirubin
    1. Usually the result of Gilbert’s Syndrome
    2. Check unconjugated and conjugated bilirubin to exclude hamolysis

Note that previous recommendations made a distinction between ALT or AST results <x2 normal and >x2 normal. The latest guidelines from the Royal Society of Gastroenterology no longer makes this distinction – as evidence suggests that the degree of elevation, and the duration of elevation does not correlate to the degree of liver disease. Therefore, any rise in these tests should be considered for further investigation. Liver disease is often “silent” until advanced.

Summary

Test Result Initial Action Management Plan
↑ Bilirubin only Check conjugated / unconjugated ratio to exclude haemolysis Reassure – likely to be Gilbert’s Syndrome
↑ gamma-GT only From history:
  • Alcohol?
  • Enzyme inducing drugs?
  • Obese?
  • Reduce alcohol intake
  • Lose weight
  • May require no action – consider repeating tests in 1-3 months
SYNTHETIC FAILURE
↑ INR
↓Albumin
↓ Platelets
  • Urgent Referral to hospital
  • In hospital – likely will have full “liver screen” of autoantibodies, ferritin, hepatitis serology
CHOLESTATIC PATTERN

↑ bilirubin

↑ ALP

↑ GGT
  • USS liver
  • Hepatitis virus serology (Hep B and C)
  • Autoimmune tests (autoantibodies and immunoglobulin)
  • Likely requires referral (non-urgent) to gastroenterology for further assessment – based on results of secondary investigations
  • May require urgent referral if systemically unwell or signs of malignancy (e.g. weight loss)
  • If all secondary tests are normal, can consider repeating initial LFTs – if resolved – no further management required
HEPATITIC PATTERN↑ ALP
ALT
AST
Further Tests:
  • Hepatitis virus serology (Hep B and C)
  • Autoimmune tests (autoantibodies and immunoglobulin)
  • Ferritin
  • USS liver
Dilated bile ducts on USS:
  • Refer for cholangiography, ERCP

Normal bile ducts:
Treat underlying disorder – e.g. viral hepatitis, autoimmune liver disease, haemochromatosis, NAFLD, Alcoholic fatty liver disease

If viral serology, autoimmune and ferritin tests are normal – likely AFLD or NAFLD – depending on risk factors

  • Reduce alcohol intake
  • Stop hepatotoxic drugs
  • Advise weight loss Weight (BMI>25)
  • Consider Fibroscan or ELF blood test
  • Consider referral for further evaluation

Adapted from a table in – Davidson’s Principles and Practice of Medicine. 20th ed. Churchill Livingstone, (2006), Boon, NA., Colledge, NR., Walker, BR. and updated with reference to Guidelines on the Management of abnormal liver blood tests by the Royal College of Gastroenterology, 2016. 

References

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