Liver Function Test (LFT) or Liver Profile Test is a test that helps to assess the function of the liver. These tests are requested when there are symptoms of liver problems or liver disease. There is no single test that can assess the liver function completely because the liver performs numerous functions in the body; therefore, the Liver function tests can be group into Liver function blood test, liver imaging test, liver biopsy, urine test and test of coagulation. Not all of these tests are done in a patient with liver disease and the test commonly done when a liver function test is requested is the blood test because it is cheaper; other ones are only requested based on the individual need of every patient coming with liver problems.
Liver Function Test Results Explained
Each of the liver function test components will be listed and explained below. The results expected in each liver disease are also mentioned; however, the values that will be shown in the pictures and also written may vary according to countries and even vary from hospitals to hospitals within the same country. You should check the values that your doctor uses or the ones used by your country or hospital.
Liver Function Test Parameters (Components)
- Blood tests
- Imaging Test
- Coagulation factors test
- Urine test
- Liver biopsy
Liver Function blood test
With breakdown of liver cells from any cause, there is release of liver enzymes and other breakdown products in the blood. These products can be measured in the blood. There is normal range of values of these enzymes or breakdown products and elevation of these liver enzymes of products above the normal range shows there is a liver problem.
Liver Function blood test components (parameters)
- Liver enzymes
- Total protein in blood since the liver produces proteins
- Albumin the major protein blood produced by the liver
- Bilirubin a byproduct of the breakdown of red blood cells: when bilirubin is conjugated (made soluble in water, it shows the problem is from the liver) when it is unconjugated (not soluble in water, then it shows it is not a problem of the liver)
- Prothrombin time: the liver produces coagulation factors (proteins prothrombin)
All these components or parameters are measured using a liver blood test.
Liver enzymes are proteins that help to speed up chemical reactions in the liver. They are involved in various reactions of the liver.
Liver Enzymes measured in Liver Function test
- Alanine Aminotransferase or Alanine Transaminase(ALT): this is found in the cytosol of the liver cells; ALT is more specific to the liver and an elevated level of ALT in the blood shows liver cell damage
- Aspartate Aminotransferase or Aspartate Transaminase (AST): this enzyme is found more in the mitochondrion (about 80%) of the liver cell than the cytoplasm (about 20%). AST is not specific to the liver cells which mean that other cells of the body also have AST such as the muscles, heart, brain and kidney. If only AST is raise with no change in ALT, it is unlikely that it is a liver disease and other organs mentioned above may be involved. But when there is elevated level of ALT and AST, it confirms the problem is from the liver.
- Alkaline phosphatase (ALP): This enzyme can be found in the canalicular and sinusoidal membranes of the liver and could also be found in other tissues of the body such as the bones, placenta and intestine. If there is abnormal values of gamma glutamyl transpeptidase together with abnormal value of ALP, then it is likely that there is a liver disease else other organs are the cause of the elevated ALP and not the liver (separation of isoenzymes by electrophoresis can be used to know the source of a raise ALP whether it is coming from the liver or bone or placenta or intestine). Serum ALP is elevated in disease conditions such as cholestasis from any cause; in cholestatic jaundice, levels of ALP may be 4 to 6 times the normal range of value. Abnormal result of ALP can be found in metastases of cancers to the liver and also in Liver cirrhosis.
- gamma-Glutamyl transpeptidase: this enzyme is elevated with alcohol consumption and use of phenytoin. When ALP levels are normal and gamma-Glutamyl transpeptidase is raised, then it is an alcohol induced liver disease.
What causes elevated liver enzymes?
Elevated liver enzymes occur following the destruction of liver cells (hepatocytes) and the subsequent release of the enzymes in the liver cells into the blood; the enzymes are then detected in blood by carrying out a Liver Function Blood Test (LFT blood test). This Liver profile blood test can only be detected when about 85% of the Liver cells have been damaged. This means that a Liver function test (LFT) does not actually detect liver damage at early stage because of the large functional reserve of the liver; this means whenever the liver cells are destroyed, the liver tries to compensate for the damage and this continues until about 85% of the cells have been destroyed before it can be detected by liver function blood test. Therefore, the damage of liver cells is the cause of elevated liver enzymes in blood; when the liver damage is severe it causes high liver enzymes.
What can cause liver enzymes to be elevated generally include anything that may cause liver damage such as alcohol, infections such as hepatitis B or hepatitis C, infestations with some worms, direct trauma to the liver, drugs (most drugs cause this) or toxins, malignancies (cancers either arising from the liver directly or metastasizing from other organs to the liver), congenital abnormalities or autoimmune reactions)
Albumin and Total Protein level in LFT
When the total proteins level of the blood is decreased with other associated abnormal liver function tests results then it shows the liver is not producing adequate proteins because its function is deranged.
When the liver function is abnormal, there will be a decrease in the level of albumin in the blood. A reduction in albumin levels causes abdominal swelling (known as ascites), or generalized swelling of the body (known as anasarca) such as in Nephrotic syndrome in which there is loss of albumin in the urine.
Bilirubin level in Liver Function Test
Bilirubin is a breakdown product of red blood cells. When red blood cells are broken down excessively, there is an elevated level of bilirubin in the blood. If elevated bilirubin occurs in liver disease, then it conjugated bilirubin (and this comes with skin itching known as pruritus in Medicine) but when elevated levels of bilirubin is unconjugated, then it is most likely caused by hemolysis that is not associated with the liver such as in sickle cell anemia crisis or sepsis.
Prothrombin Time (PT)
This is measured because the liver produces prothrombin which is involved in the clotting pathway. Low levels of prothrombin are produced in liver disease and because of this; there will be prolong prothrombin time.
There are various other liver blood tests that can be done based on the type of liver disease involved and the need for such test but the ones commonly done have been explained above.
Imaging Test for Liver Function
The use of ultrasound, magnetic resonance imaging (MRI) and Computed Tomographic (CT) scanning are very useful for assessing the structural integrity of the liver. CT scan or Ultrasound can be used to guide liver biopsy procedure. Ultrasound is useful in detecting hepatomegaly, splenomegaly, gallstones, focal liver disease that is greater than 1 cm, and lymph node enlargement.
Urine Test for Liver Function
When bilirubin becomes conjugated, it can be excreted in urine, this changes the color of urine to deep yellow and it is called bilirubinuria. Other pigment detected in liver disease in urine is urobilinogen. These pigments are detected by a urine dipstick (Urinalysis)
A liver biopsy shows the architectural integrity of the liver. Biopsy and histology helps to show the presence of cancer cells, the type of cancer cells and the integrity of the structure of the liver. Diagnosis of focal liver disease may be missed using liver biopsy. It is suitable for diffused (wide spread) disease of the liver. Complications such as bleeding (hemorrhage) may occur and may be life threatening.
Of all the Liver function Tests, the blood tests are commonly requested because they are cheaper and can be used for screening before other tests are done for confirmation.