Liver Function Tests: Purpose, Procedure, and Results​

Written by Dr. Lynda Odoh - Anikwe on Fri, 11 November 2022

Key Highlights

  • The liver is responsible for detoxification, digestion, releasing blood-clotting proteins, and much more.
  • If anyone has nausea, vomiting, abdominal pain, dark-colored urine, yellowing eye whites, skin and nails, they might be having liver dysfunction issues.
  • There are some enzymes and proteins that maintain liver function. Abnormal levels of these indicate liver damage.
  • Enzymes like alanine transaminase (ALT), aspartate transaminase (AST), alkaline phosphatase (ALP), and gamma-glutamyltransferase (GGT), proteins like albumin, prothrombin, and a waste product such as bilirubin are markers of liver function.

Do you feel abdominal pain, nausea or vomiting, mild fever, loss of appetite, dark urine color, pale stool color, skin, eyes, and nails appearing yellowish? If any of these symptoms appear, consult your doctor about liver function tests.

These symptoms indicate you might be in the initial stages of liver disease. There are several types of liver function tests, including types of liver scans and types of liver blood tests. These tests analyze the functioning capacity of the liver based on the amounts of certain substances produced by it.

To understand liver function tests, you should first understand what the liver does.

Functions of the liver

The liver is a vital organ of the body. It is situated on the upper-right side of your abdomen under your rib cage. The liver is responsible for more than 500 important activities.

Some of the activities are mentioned below:

  • The liver helps to regulate the chemical level in the body.
  • The liver is responsible for removing all the toxins from the blood.
  • The liver involves the regulation of amino acids, which helps in the production of proteins for blood.
  • Cleaning of drugs or other harmful substances from the blood. Byproducts are excreted as bile.
  • The liver helps in the metabolism process and digesting of food.
  • The liver regulates blood clotting activity.
  • Poisonous ammonia is converted into urea in the liver.

Bile secretion is an important endpoint of liver function, and liver dysfunction affects bile production. These functions may be disrupted by various factors that damage the liver, such as viruses, alcohol consumption, and obesity.

Purpose of liver function tests

Liver function tests are blood tests and scans used to check for liver damage and measure the level of enzymes in your body.

The levels of various enzymes and proteins in your blood are a measure of your liver function. If the numbers are higher or lower than liver test normal range, then that suggests liver trouble.

The purpose of liver function test covers:

  • Diagnosis of liver illnesses, including hepatitis
  • Keeping track of liver disease treatment, as these tests can reveal how the treatment is affecting the patient
  • Examining how badly a disease like cirrhosis has destroyed or scarred the liver
  • Monitoring the negative effects of certain drugs

Common liver function tests

When you have symptoms of liver dysfunction and you visit your doctor, he or she may recommend some liver function tests.

A blood sample is usually taken from a vein in your arm. Some common liver function tests include:

Enzyme tests

  • Aminotransferases -

AST and ALT are two aminotransferases. They are hepatocellular injury markers. The liver, cardiac muscle, skeletal muscle, kidneys, brain, pancreas, lungs, leucocytes, and red cells all contain AST enzymes.

ALT is an enzyme found in large quantities in the liver. The release of these enzymes into the circulation is triggered by hepatocellular damage, not necessarily cell death. Normally, males have greater AST and ALT levels than females.

  • Alanine transaminase (ALT) -

ALT is a liver enzyme that is used in the conversion of proteins into energy for the liver cells. ALT is released into the bloodstream when the liver is injured, and its levels rise, which indicates liver damage. That's why the optimum presence range of Alanine transaminase is 0 to 45 IU/L.

This range can be slightly differ among females and children. Above 45IU/L can damage the liver badly and interrupt its activities.

  • Aspartate transaminase (AST) -

AST is an enzyme that aids in the digestion of amino acids. AST, like ALT, is found in the blood at low levels. Increased AST values could indicate liver or muscle damage. The optimum range of Aspartate transaminase should be not more than 0 to 35 IU/L. For children, this range may be slightly higher.

  • Alkaline phosphatase (ALP) -

ALP is an enzyme that breaks down proteins and is found in the liver and bones. ALP levels that are higher than usual can suggest liver injury or diseases, such as a blocked bile duct or certain bone diseases. The optimum range of Alkaline phosphatase is 30 to 120 IU/L, and a rise above this level may induce liver diseases.

  • Gamma-glutamyltransferase (GGT) -

GGT is a circulating enzyme. Higher-than-normal levels could suggest damage to the liver or bile ducts. A high level of these enzymes could damage the liver function or bile ducts. Gamma-glutamyltransferase should be in the range of 0 to 30 IU/L.

  • L-lactate dehydrogenase (LD) -

The enzyme LD is present in the liver. Increased levels can suggest liver disease, but they can also be elevated in a variety of other conditions. This is an enzyme found in nearly every cell in the body. When cells are destroyed by disease or injury, LD is released into the bloodstream. The optimum range of L-lactate dehydrogenase is 122 to 222 U/L. A level above that is harmful to the liver.

Protein tests

  • Albumin and total protein -

The liver produces numerous proteins, including albumin. Albumin is made in the liver, which produces about 10gm per day. Serum albumin levels drop with any type of liver illness, indicating decreased production. A low level of these proteins could damage liver function. Albumin and total protein range should be 40 to 60 g/L.

  • Prothrombin time (PT) -

The time it takes for your blood to clot shows the level of prothrombin, which is involved in the blood-clotting process. Increased PT can signal liver disease, but it can also be caused by blood-thinning medications like warfarin. The ideal blood-clotting time should be 10.9 to 12.5 seconds. More than that shows a low level of prothrombin in the body.

  • Bilirubin -

Bilirubin is a waste product made by the liver. Conjugated bilirubin is water-soluble and eliminated in the urine. It is converted to bilirubin glucuronide in the liver and then released into bile and the gut, respectively. A high level of bilirubin can leak out from the liver if the liver is damaged. This condition causes jaundice.

In jaundice, skin and eye color turns yellow and urine gets darker in color. A general range of bilirubin in the body should be 2 to 17 micromoles/L.

Meaning of liver test results

The doctor will use these results to determine the proper treatment or diagnose your condition, including:

  • Hepatitis A
  • Hepatitis B
  • Hepatitis C
  • Liver cancer
  • Alcohol-induced liver damage

If someone has a liver disorder, a liver function test can help to determine the progress of the disease and the effect of medication.

No one test can examine all the aspects of liver function.

Preparing for a liver function test

A doctor will suggest that you go on an empty stomach for a liver function test. Your doctor may ask you to avoid certain food items and medicines that can affect the results of the blood test. You can drink water before the test.

Procedure of a liver function test

Your pathology care technician will clean your skin before giving an injection to decrease the risk of any microbial infection.

Then s/he will wrap an elastic strap on your upper arm. This will help the path lab technician to see your veins.

A tiny needle will be used to draw blood from a vein in your arm. A small amount of blood will be collected into a test tube or vial once the needle is inserted. When the needle goes in or out, it may sting a little. After this, the technician puts a bandage on the puncture site. This normally takes under 5 minutes.

Risks of a liver function test

Your liver function test carries very little risk. You may experience a little pain or bruising where the needle was inserted, but the pain fades within about 10 minutes.

Different types of liver scans

  • Computer tomography (CT) scan

A CT scan utilizes X-rays and sophisticated computer technology to make picture slices (cross-sectional views) of your liver with the use of a specific dye. CT scans reveal vital details about organ structure, such as the health of blood veins in your liver, while reducing radiation exposure.

If you have chronic liver disease and cannot take the dye used in CT scans, the lab can perform alternative tests, such as special ultrasounds.

  • Ultrasound scans

Ultrasound tests are used to examine your liver's structure for any signs of damage (cirrhosis); damage to any other abdominal organ, such as your pancreas; any cancer indications, such as masses.

For those with advanced liver illness who cannot undergo a CT scan, there is the Doppler ultrasound, which employs a specific dye. Doppler ultrasonography is a type of ultrasound that displays blood flow through the liver.

Clinical significance of liver function tests

If you have some other disease or condition, it will affect your liver function tests. Abnormalities in liver enzymes are found in several conditions. If repeated testing reveals abnormalities, more research is required.

Some of the factors that affect liver function are:

Medications: A number of medicines have been linked with liver damage. Many of these are used by people in day-to-day life, such as non-steroidal anti-inflammatory drugs (NSAIDs), antibiotics such as tetracycline, anti-tuberculosis drugs, antifungal drugs such as ketoconazole, anti-depressant such as fluoxetine, and antiviral such as ritonavir. Long-term use of these medicines may result in liver damage.

Methotrexate, a common rheumatoid arthritis and other inflammatory arthritis medicine, can cause a moderate transitory rise in liver function test values (LFTs). It can also cause irreversible liver damage in patients with liver fibrosis and cirrhosis, especially at large cumulative dosages. LFTs can be elevated by the excessive use of herbal medicines.

Alcohol: If you have any disease and you consume alcohol, it will slightly elevate the ratio of AST to ALT by 2:1. A high level of AST indicates an alcoholic liver disorder. The peak in GGT along with AST can indicate alcohol abuse.

Hepatitis induced by the autoimmune system: Women are more likely to have hepatitis than men. The patient frequently has elevated LFTs for no obvious reason. Anti-smooth muscle antibodies and anti-liver/kidney microsomal antibodies get activated to the liver antigen, and they might all be indicated by elevated LFTs.

Fatty liver disease: If you have fatty liver disease, then you are also suffering from overweight, diabetes, or dyslipidemia, with no evidence of clinically more alcohol consumption. Other liver function tests may be normal, but the AST and ALT may both be elevated with a 1:1 ratio.


Liver function tests help assess how well your liver is working. You should seek a medical consultation and undergo test as soon as any symptoms of liver damage become evident. There are a variety of blood tests and scans that create a comprehensive picture of liver function.


Dr. Lynda Odoh - Anikwe

Dr. Lynda Odoh - Anikwe (M. B. B. S) is a MPH  candidate at the University of Manchester. Dr Odoh is also currently a member of the Society of Lifestyle Medicine Nigeria, and aiming to get certified by the International board of lifestyle medicine as a Lifestyle Medicine Physician by the last quarter of 2022.

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