Blood tests that monitor and identify liver damage or sickness are known as liver function tests. Specific proteins and enzyme levels in the blood are measured through these tests. Some tests determine how well the liver functions by examining its two regular activities—producing protein and eliminating a blood waste material called bilirubin. Other liver function tests look at the enzymes the liver cells produce in response to sickness or injury.

Types of tests
Liver function tests can identify different diseases by detecting high or low levels of various substances. Doctors can recommend the following tests:

Alanine transaminase (ALT) test: ALT is a liver enzyme that aids in converting proteins into energy for the liver cells. When the liver is damaged, ALT is released into the bloodstream, where it accumulates.

Aspartate transaminase (AST) test: AST is an enzyme that aids in the metabolism of amino acids. Usually, AST, like ALT, is present in low levels in the blood. A rise in AST levels could indicate liver damage, disease, or muscle damage.

Alkaline Phosphatase (ALP) test: ALP is an enzyme found in the liver and bone that aids in the breakdown of proteins. ALP levels that are higher than normal may indicate liver damage or diseases, such as a blocked bile duct or bone disease.

Gamma-glutamyl transferase (GGT) test: GGT is another enzyme, and higher GGT levels may indicate a bile duct or liver disorder.

Lactate dehydrogenase (LDH) test: Elevated levels of this enzyme can indicate a wide range of diseases in addition to liver damage.

Prothrombin time (PT) test: PT is the amount of time it takes for your blood to coagulate. The use of specific blood thinners such as warfarin can also cause increased PT, which can be a symptom of liver damage.

Total protein and albumin test: Albumin is one of several proteins produced in the liver. The body needs these proteins to fight infections and execute other functions. Albumin and total protein levels that are below normal could be a sign of liver illness or injury.

Procedure
For conducting these tests, a tiny sample of blood is taken from a vein in the arm by a healthcare professional and tested at a lab. Experts look for unusually high or low concentrations of various chemicals and compare the amounts of various proteins or enzymes. They may be able to better understand what might be happening in the liver if the balance is off. Liver function tests should be conducted at a hospital or a specialist testing center. The professional will locate a vein in the arm to draw blood and clean the area. They may tie a compression band around your arm to easily locate the vein.

The professional will use a tiny needle to collect blood from a vein in the arm and place it in a vial. The whole procedure takes a short while. The blood sample will be sent to a lab for evaluation. Depending on whether the lab is housed in the same building or somewhere else, one can get the results in a few minutes or several days.

Test results
For typical liver function tests, normal blood test outcomes include:

ALT: 7 to 55 units per liter (U/L)

AST: 8 to 48 U/L

ALP: 40 to 129 U/L

Albumin: 3.5 to 5.0 grams per deciliter (g/dL)

Total protein: 6.3 to 7.9 g/dL

Bilirubin: 0.1 to 1.2 (mg/dL)

GGT: 8 to 61 U/L

LDH: 122 to 222 U/L

PT: 9.4 to 12.5 seconds

These are the normal ranges for men. Normal outcomes may differ for women and children.

Interpretation of results

1. High amounts of ALT are present in hepatocytes and are released into the blood as a result of hepatic damage. Consequently, liver function tests serve as a helpful indicator of hepatocellular damage.
2. The liver, bile duct, and bone tissues contain the highest concentrations of ALP. The enzyme is usually elevated in liver pathology due to increased production in reaction to cholestasis. So, ALP is a helpful indirect indicator of cholestasis.
3. An increase in bilirubin suggests a pre-hepatic cause of jaundice. An isolated increase in bilirubin can be brought on by Gilbert’s syndrome. Hemolysis is another condition that can lead to a rise in bilirubin levels. However, blood film, complete blood count, reticulocyte count, haptoglobin, and LDH levels should be checked to confirm hemolysis.
4. An elevated PT can be a sign of liver disease and dysfunction in the absence of other secondary causes, such as the use of anticoagulant treatments or a vitamin K deficiency.
5. Liver disease can cause a reduction in albumin production, which can cause albumin levels to drop.

To know more about liver function tests, one should consult a doctor.