Liver function tests (LFTs), are a group of blood tests that provide valuable information about the health and function of the liver. The tests measure the levels of various enzymes and proteins in the blood. Some of the parameters of an LFT will also tell you how well your liver is performing its various functions such as producing protein or eliminating bilirubin, a blood waste product. An LFT also measures how much enzymes are being releases in response to liver damage. A point to be noted is how some irregularities in an LFT doesn’t always mean liver disease because there are several external factors that can affect the results, in which case a doctor is the best person to interpret the results considering your current health status. The main parameters of a standard liver function test typically include:
ALANINE AMINOTRANSFERASE (ALT) or SGPT
ALT or is an enzyme found mainly in the liver that helps convert proteins into energy for the liver cells. When liver cells are damaged, they release ALT into the bloodstream which means high levels of ALT indicate liver injury, nonalcoholic fatty liver, cirrhosis, hepatitis, or other liver disease. Low than usual ALT levels could indicate a vitamin B6 deficiency or chronic kidney disease.
NORMAL LEVELS OF ALT: 7 to 55 units per liter (U/L), although it depends on the reference levels of the laboratory.
ASPARTATE AMINOTRANSFERASE (AST) or SGOT
AST is another enzyme found in the liver, heart, pancreas, muscles, and other tissues. SGOT stands for Serum Glutamic Oxaloacetic Transaminase, which is also known as AST (Aspartate Aminotransferase). It is an enzyme found in various tissues of the body, with higher concentrations in the liver, heart, pancreas, muscles, brain, and kidneys. SGOT or AST is released into the bloodstream when these tissues are damaged. In a liver function test, elevated AST levels can be a sign of liver disease and liver damage.
NORMAL LEVELS OF AST: The common normal range of AST is 8 to 33 U/L for adults. However, results can vary depending on lab references and other factors including your age, weight, sex, and race.
SGPT:SGOT RATIO
The SGPT/SGOT ratio, or AST/ALT ratio, is a medical parameter calculated by dividing the SGPT (ALT) level by the SGOT (AST) level. The ALT /AST ratio is an extended indicator to help diagnose various liver conditions, including hepatitis, cirrhosis, and liver damage caused by alcohol or medications.
SGPT/SGOT ratio <1 (i.e., ALT is higher than AST): possible liver damage, viral hepatitis, or fatty liver disease.
SGPT/SGOT ratio >1 (AST is higher than ALT): Possible alcoholic liver damage or cirrhosis.
BILIRUBIN
Bilirubin is a yellowish pigment that forms during the breakdown of red blood cells in the body. When red blood cells complete their life cycle, they are broken down, and one of the byproducts is bilirubin. This bilirubin is then transported to the liver, where it undergoes further processing and is eventually excreted from the body. There are two main types of bilirubin: unconjugated (indirect) bilirubin and conjugated (direct) bilirubin.
NORMAL LEVELS OF BILIRUBIN
Total Bilirubin: 0.1 to 1.2 mg/dL (1.71 to 20.5 µmol/L)
Direct (Conjugated) Bilirubin: Less than 0.3 mg/dL (less than 5.1 µmol/L)
Unconjugated (Indirect): Bilirubin: 0.2 to 0.8 mg/dL.
Elevated levels of bilirubin can indicate liver dysfunction or problems with the bile ducts such as gall stones. Low levels of bilirubin or (hypobilirubinemia) can be caused by medications, caffeine, or autoimmune diseases such as rheumatoid arthritis, lupus, polymyositis, Sjogren’s syndrome or even cardiovascular disease. High bilirubin can also help determine sickle cell disease or other conditions that cause hemolytic anemia in which red blood cells are destroyed faster than they’re made.
TOTAL PROTEIN
This measures the total amount of protein in the blood, including albumin, globulin, and other proteins. Abnormal levels can indicate liver or kidney disease.
TOTAL PROTEIN NORMAL LEVELS: 6.0 to 8.3 grams per deciliter (g/dL) or 60 to 83 g/L.
ALBUMIN
Albumin is a protein produced by the liver. It helps move many small molecules through the blood, including bilirubin, calcium, progesterone, and some medicines. It plays an important role in keeping the fluid in the blood from leaking into the organs and tissues. Low levels of albumin can be a sign of liver disease or malnutrition.
NORMAL LEVELS OF ALBUMIN: 3.5 to 5.5 g/dL. Lower albumin indicates malnutrition, liver disease, kidney disease, or an inflammatory disease. Higher albumin levels may be caused by acute infections, burns, and stress from surgery or a heart attack. It also indicates dehydration.
Tests recommended along with albumin are C-reactive protein, or CRP, Alpha-1 acid, Glycoprotein, or a1-AG, Ferritin, and Ceruloplasmin.
SERUM GLOBULIN
Globulins are proteins produced by the liver immune system in your blood. Globulins contribute to liver function, blood clotting, and fighting infection. There are different types of globulins called alpha, beta, and gamma globulins. High levels may indicate autoimmune disease, infections, or cancer. A low globulin reading may be a sign of liver disease, kidney disease or malnutrition. Eating lean protein, such as fish, can increase total protein levels and low globulin. Boosting the consumption of foods that aid liver and kidney detoxification is also beneficial in low globulin.
NORMAL LEVELS: 2.0 to 3.5 g/Dl.
GLOBULIN/ALBUMIN RATIO
The A/G ratio measures the amount of albumin proteins in blood compared to globulins. Your body has slightly more albumin than globulins and the AG ratio test is also an indicator to help diagnose kidney disease, liver disease, or nutritional problems. Further kidney function tests are usually suggested to rule out the possibility or confirm kidney disease.
NORMAL LEVEL: A normal A/G ratio is between 1.1 and 2.5 (Can vary from lab to lab)
A low A/G ratio indicated inflammation or certain cancer such as myeloma. A high A/G ratio may indicate kidney disease, antibody deficiencies, or severe dehydration. A low A/G ratio indicates inflammation, kidney disease, liver disease, chronic infections like human immunodeficiency virus (HIV), autoimmune diseases like lupus, and certain cancers. The A/G ratio can be decreased with short-term problems that cause inflammation, such as tissue trauma or infection, chronic inflammatory conditions, and nutritional problems.
PROTHROMBIN TIME (PT) OR INTERNATIONAL NORMALIZED RATIO (INR)
These tests measure how long it takes for blood to clot. The liver produces clotting factors, so abnormal results may indicate liver dysfunction.
GAMMA-GLUTAMYL TRANSFERASE (GGT)
Gamma-Glutamyl Transferase (GGT), also known as gamma-glutamyl transpeptidase, is an enzyme found in various tissues, with higher concentrations in the liver. GGT plays a role in the metabolism of glutathione, a molecule that helps protect cells from oxidative damage. Elevated GGT levels can be associated with liver and biliary tract disorders, as well as alcohol consumption. Low GGT levels probably means you don’t have liver disease, although it is best to compare the results with an alp test. It is important to note that GGT is not as liver-specific as some other enzymes (such as ALT or AST), and elevated levels can also be associated with conditions affecting other organs.
NORMAL LEVELS: In adults, normal GGT levels are in the range of 0 to 30 IU/L. Anything above 30 IU/L could be a sign that your liver isn’t working well.
SERUM AMMONIA
Ammonia is a waste product processed in your liver and removed through your urine. A buildup of ammonia in your blood is a serious health concern indicating liver disease, kidney failure and certain congenital conditions. It is most used to diagnose and monitor hepatic encephalopathy , a severe liver disease.
PLATELET COUNT
Liver disease can affect platelet production, so a low platelet count may indicate liver problems such as NAFLD ( Non alcoholic fatty liver disease), hepatitis, cirrhosis, megaloblastic anemia and others.
FACTORS THAT IMPACT A LIVER FUNCTION TEST
There are several factors that can create abnormal results in a liver function test.
NAFLD
Alcohol
Viral infection
Underlying diseases or conditions
All these parameters in a liver function test provide a comprehensive view of liver function and health. Interpretation of the results should be done by a healthcare professional, as elevated or abnormal levels may indicate various liver conditions, including hepatitis, cirrhosis, fatty liver disease, and others. Additional tests may be necessary to confirm a diagnosis and determine the underlying cause of liver dysfunction.