Liver function tests (LFTs or LFs) are groups of blood tests that give information about the state of a patient’s liver. These tests include prothrombin time (PT/INR), aPTT, albumin, bilirubin (direct and indirect), and others. Liver transaminases (AST or SGOT and ALT or SGPT) are useful biomarkers of liver injury in a patient with some degree of intact liver function. Most liver diseases cause only mild symptoms initially, but these diseases must be detected early. Hepatic (liver) involvement in some diseases can be of crucial importance. This testing is performed on a patient’s blood sample. Some tests are associated with functionality (e.g., albumin), some with cellular integrity (e.g., transaminase), and some with conditions linked to the biliary tract (gamma-glutamyl transferase and alkaline phosphatase). Several biochemical tests are useful in the evaluation and management of patients with hepatic dysfunction. These tests can be used to detect the presence of liver disease, distinguish among different types of liver disorders, gauge the extent of known liver damage, and follow the response to treatment.
Causes of Liver Function Tests
More common causes of abnormal liver enzymes include
- Over-the-counter pain medications, particularly acetaminophen (Tylenol, others)
- Certain prescription medications, including statin drugs used to control cholesterol
- Drinking alcohol
- Heart failure
- Hepatitis A
- Hepatitis B
- Hepatitis C
- Nonalcoholic fatty liver disease
Other causes of elevated liver enzymes may include:
- Alcoholic hepatitis (severe liver inflammation caused by excessive alcohol consumption)
- Autoimmune hepatitis (liver inflammation caused by an autoimmune disorder)
- Celiac disease (small intestine damage caused by gluten)
- Cytomegalovirus (CMV) infection
- Epstein-Barr virus
- Hemochromatosis (too much iron stored in your body)
- Liver cancer
- Polymyositis (inflammatory disease that causes muscle weakness)
- Sepsis (an overwhelming bloodstream infection that uses up neutrophils faster than they can be produced)
- Thyroid disorders
- Toxic hepatitis (liver inflammation caused by drugs or toxins)
- Wilson’s disease (too much copper stored in your body)
Liver Function Test
Liver tests can help determine if your liver is not working correctly? The liver performs a number of vital bodily functions, such as:
- Removing contaminants from your blood
- Converting nutrients from the foods you eat
- Storing minerals and vitamins
- Regulating blood clotting
- Producing proteins, enzymes, and bile
- Making factors that fight infection
- Removing bacteria from your blood
- Processing substances that could harm your body
- Maintaining hormone balances
Problems with the liver can make a person very sick and can even be life-threatening.
Symptoms of liver problem
Symptoms of a liver disorder include
Types of Tests
There are a number of liver function tests, with lots of complex names. You might hear your doctor or nurse mention some of the common ones, which include:
- Alanine transaminase (ALT) test – ALT is an enzyme that helps break down proteins and is found mainly in your liver. High levels in your blood could mean you have liver damage.
- Alkaline phosphatase (ALP) test – ALP is an enzyme you have in your liver, bile ducts, and bone. You might have high levels if you have liver damage or disease, a blocked bile duct, or bone disease.
- Albumin and total protein test – Your liver makes two main proteins: albumin and globulin. Low levels can mean damage or disease.
- Aspartate transaminase (AST) test – AST is another enzyme found in your liver. High blood levels could be a sign of damage or disease.
- Bilirubin test – Bilirubin is made when red blood cells break down. Usually, the liver cleans bilirubin out of your body. If you have high levels in your blood, a problem called jaundice, you may have liver damage.
- Gamma-glutamyltransferase (GGT) test – High levels of the GGT enzyme could point to liver or bile duct damage.
- L-lactate dehydrogenase (LD) test – LD is another enzyme that’s high when you have liver damage, but other conditions can raise its level, as well.
- Prothrombin time (PT) test – This test measures how long it takes your blood to clot. If it takes a long time, that could be a sign of liver damage. Medications that thin your blood, such as warfarin (Coumadin), can also lead to a longer PT.
- Coagulation panel (prothrombin time or PT, and international normalized ratio or INR) – These tests measure blood’s ability for normal clotting and prevention of bleeding and bruising. This is the function of certain proteins called clotting factors that normally are produced in the liver. Normal values are about 9.5 to 13.8 seconds.
- Albumin level (hypoalbuminemia) – Albumin is a very common protein found in the blood with a variety of functions. It also is produced only in the liver, and if its levels are lower than normal it can be suggestive of chronic liver disease or liver cirrhosis. Of note, many conditions other than liver disease also may cause low albumin levels. Normal values are about 3.5 to 5 g/dL.
- Bilirubin – This molecule is a byproduct of the routine destruction of red blood cells occurring in the liver. It is normally released as bile in the feces. Elevation of the bilirubin can suggest liver dysfunction. However, other conditions with increased destruction of red blood cells also can cause elevated bilirubin levels despite normal liver function. Normal values are about 0.1 to 1.0 mg/dL.
Increased total bilirubin (TBIL) causes jaundice, and can indicate a number of problems:
- 1. Prehepatic – Increased bilirubin production can be due to a number of causes, including hemolytic anemias and internal hemorrhage.
- 2. Hepatic – Problems with the liver are reflected as deficiencies in bilirubin metabolism (e.g., reduced hepatocyte uptake, impaired conjugation of bilirubin, and reduced hepatocyte secretion of bilirubin). Some examples would be cirrhosis and viral hepatitis.
- 3. Posthepatic – Obstruction of the bile ducts is reflected as deficiencies in bilirubin excretion. (Obstruction can be located either within the liver or in the bile duct).
- If direct (conjugated) bilirubin is normal, then the problem is an excess of unconjugated bilirubin (indirect bilirubin), and the location of the problem is upstream of bilirubin conjugation in the liver. Hemolysis, or internal hemorrhage can be suspected.
- If direct bilirubin is elevated, then the liver is conjugating bilirubin normally, but is not able to excrete it. Bile duct obstruction by gallstones, hepatitis, cirrhosis or cancer should be suspected.
This table shows examples of some combinations of results that may be seen in certain types of liver conditions or diseases.
|Type of liver condition or disease||Bilirubin||ALT and AST||ALP||Albumin||PT|
|Acute liver damage (due, for example, to infection, toxins or drugs, etc.)||Normal or increased usually after ALT and AST are already increased||Usually greatly increased (> 10 times); ALT is usually higher than AST||Normal or only moderately increased||Normal||Usually normal|
|Chronic forms of various liver disorders||Normal or increased||Mildly or moderately increased; ALT is persistently increased||Normal to slightly increased||Normal||Normal|
|Alcoholic Hepatitis||Normal or increased||AST is moderately increased, usually at least twice the level of ALT||Normal or moderately increased||Normal||Normal|
|Cirrhosis||May be increased but this usually occurs later in the disease||AST is usually higher than ALT but levels are usually lower than in alcoholic disease||Normal or increased||Normal or decreased||Usually prolonged|
|Bile duct obstruction, cholestasis||Normal or increased; increased in complete obstruction||Normal to moderately increased||Increased; often greater than 4 times what is normal||Usually normal but if the disease is chronic, levels may decrease||Usually normal|
|Cancer that has spread to the liver (metastasized)||Usually normal||Normal or slightly increased||Usually greatly increased||Normal||Normal|
|Cancer originating in the liver (hepatocellular carcinoma, HCC)||May be increased, especially if the disease has progressed||AST higher than ALT but levels lower than that seen in alcoholic disease||Normal or increased||Normal or decreased||Usually prolonged|
|Autoimmune||Normal or increased||Moderately increased; ALT usually higher than AST||Normal or slightly increased||Usually decreased||Normal|
If a person is taking drugs that may affect their liver, then abnormal test results may indicate a need to reevaluate the dosage or choice of medication. When a person with liver disease is being monitored, then the healthcare practitioner will evaluate the results of the liver panel together to determine if liver function or damage is worsening or improving.A prolonged or increased PT can be seen with liver disease, vitamin K deficiency, use of drugs to reduce risk of clotting (warfarin), and with coagulation factor deficiencies.
- Platelet count – Low platelet count (thrombocytopenia) has many causes, one of which can be advanced liver disease. Normal platelet counts are about 150,000 to 400,000 per (µL).
- Glucose – Glucose level is maintained in the body by a variety of mechanisms. The liver can release glucose in the blood for nourishment of other cells in case of starvation with insufficient oral intake of glucose. This process, called gluconeogenesis, is another major function of the liver. In advanced liver disease, this function of the liver can be compromised leading to unusually low glucose levels in the absence of adequate oral intake. Conversely, a large number of people with liver cirrhosis become glucose intolerant and develop diabetes.
- GGT (Gamma-glutamyl transpeptidase) – This enzyme is thought to indicate possible liver damage; the higher the abnormal level, the more likely there is liver damage. Normal levels of GGT are about 9 to 48 U/L.
- ALP (alkaline phosphatase) – The liver synthesizes the highest amounts of this enzyme so high levels in the blood may suggest liver injury among other causes. Normal levels of ALP are about 45 to 115 U/L.
- LD or LDH (Lactate dehydrogenase) – This enzyme may be elevated in many types of diseases, including liver disease. Normal levels are about 122 to 222U/L
|Liver Function Tests (LFT)|
|Conjugated (D. Bilirubin)||0-0.35||MG/DL|
|Unconjugated (I.D. Bilirubin)||0.2-0.65||MG/DL|
Normal blood test results for typical liver function tests include
- ALT. 7 to 55 units per liter (U/L)
- AST. 8 to 48 U/L
- ALP. 45 to 115 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 milligrams per deciliter (mg/dL)
- GGT. 9 to 48 U/L
- LD. 122 to 222 U/L
- PT. 9.5 to 13.8 seconds
These results are typical for adult men. Normal results vary from laboratory to laboratory and might be slightly different for women and children.