Liver function tests Flashcards
Give the four main functions of the liver
Synthesis
Detoxification
Immune function
Storage
What compounds does the liver synthesise?
Clotting factors
Bile acids
Carbohydrates (glucose, glycogen)
Proteins (albumin)
Lipids (cholesterol, lipoprotein, tryglyceride)
Hormones (angiotensinogen, insulin-like growth factor)
Describe the detoxification function of the liver
Urea production from ammonia
Detoxification of drugs (e.g. alcohol)
Bilirubin metabolism from breakdown of haemoglobin
Breakdown of insulin and other hormones
Describe the immune function of the liver
Combating infection (primarily infectious particles that are absorbed through the gut wall or from arterial blood)
Cleaning blood of particles/infections including bacteria
Neutralising and destroying drugs and toxins
What compounds does the liver store?
Glycogen
Vitamins A, D, B12, K
Copper, Iron
List the main liver function tests
Bilirubin Aminotransferases Alkaline phosphate Gamma GT Albumin Prothrombin time Creatinine Platelet count
What is the normal range for bilirubin?
1-20umol/L
What is the normal range for albumin?
35-50g/L
What are the normal ranges for aminotransferase enzymes?
5-55 U/L
Which two aminotransferase enzymes are tested for? What is the main difference between them?
Alanine aminotransferase (ALT) Aspartate aminotransferase (AST)
ALT is very specific to liver disease whereas AST can indicate muscle damage elsewhere in the body
Where is bilirubin produced?
In the spleen (by macrophages)
In the liver (Kupfer cells)
Give the main causes of raised serum bilirubin
Prehepatic: excessive RBC breakdown
Hepatic: parenchymal damage, e.g. by alcohol, cirrhosis, hepatitis
Post-hepatic: obstruction of the bile duct
What might be indicated by altered albumin levels?
Low albumin: chronic liver disease (although there are other causes e.g. renal disease, malnutrition/malabsorption, severe inflammation/shock)
High albumin: dehydration
What is the normal range for alkaline phosphatase (ALP)?
30-130 U/L
When would Gamma GT level be considered raised?
When it is higher than 35 U/L
Where are aminotransferases normally found, and what does it suggest if serum levels are raised?
Usually found inside the hepatocytes
Therefore raised serum levels indicates liver damage, e.g. in chronic liver disease or cirrhosis
Levels are very high in hepatitis; can be 20-50 times higher than normal
Describe how aminotransferase ratios can indicate disease
ALT > AST indicates chronic liver disease
AST > ALT indicates cirrhosis
Ratio >2 suggests alcoholic liver disease
Explain the meaning of increased alkaline phosphatase (ALP) in the plasma
Usually means damage to the lining of the bile duct or to bone (ALP is found in large concentrations in these cells)
Largely elevated in bile duct obstruction (or injury)
Slightly raised in liver disease
What test is done alongside ALP to distinguish between liver/biliary disease and bone disease?
Gamma GT; if GGT is normal then raised ALP is most likely to be caused by bone disease
What is prothrombin time a marker of?
Synthetic function of the liver:
The liver synthesises and secretes clotting factors, so if it’s failing, levels of clotting factors will decrease and prothrombin time will increase
Give a use for testing prothrombin time
Useful in staging liver disease to distinguish whether a patient is in need of a transplant
What is the most likely cause of jaundice if Alkaline Phosphatase (ALP) is raised?
Obstructive (post-hepatic) jaundice
e.g. gallstones, stricture, sclerosing cholangitis, pancreatitis, tumour blocking the bile duct.
What test (besides serum bilirubin) can be done to diagnose hepatic and post-hepatic jaundice?
Urinary bilirubin
- may be high in hepatic
- high post-hepatic
- no urinary bilirubin in pre-hepatic jaundice
What investigation should always be done in a patient presenting with jaundice?
Abdominal ultrasound
