The liver is an organ about the size of a football. It sits just under your rib cage on the right side of your abdomen. The liver is essential for digesting food and ridding your body of toxic substances. Liver disease can be inherited (genetic). Liver problems can also be caused by a variety of factors that damage the liver, such as viruses, alcohol use and obesity.
Enzymes are proteins found in your body that speed up certain chemical reactions. Liver enzymes perform these jobs within the liver. Two of the common ones are known as “AST” and “ALT.”
If the liver is damaged, AST and ALT pass into the bloodstream. When your provider looks at the results from your blood tests, AST and ALT values are higher than normal if your liver is damaged. The damage to the liver can come from viruses, such as the hepatitis C virus, over-the-counter drugs, and prescription and street drugs.
If your provider starts you on a certain medication, they may need to monitor your blood chemistries to make sure the medication is not causing further harm to your liver.
What Is a Liver Function Test?
A liver function test is one of a group of tests that check levels of certain enzymes and other proteins in your blood. Some of the tests look for enzymes that you’d find in your blood only when your liver is damaged or has a disease.
Others check that the organ is working the way it should. Your liver does all kinds of work that’s crucial for your health. It helps break down food, clean your blood, make proteins, and store energy. If something goes wrong with it, you might have a number of symptoms, from yellow skin to slurred speech. That’s when you might need a liver test.
If a person’s blood test results show elevated liver enzymes, a doctor will investigate possible underlying causes. They may do further tests in addition to asking about a person’s lifestyle and dietary habits. The most common cause of elevated liver enzymes is fatty liver disease. Research suggests that 25–51% of people with elevated liver enzymes have this condition.
Other health conditions that typically cause elevated liver enzymes include:
- metabolic syndrome
- hepatitis
- alcohol or drug use disorder
- cirrhosis, which is liver tissue scarring
What if my liver enzymes stay elevated?
If your liver enzymes are still elevated after six months, your doctor may do more blood tests or an ultrasound. He or she also might want you to see another doctor who specializes in the digestive system. This doctor will check for other causes and may also do a liver biopsy.
Fatty liver disease
Fatty liver disease occurs when fats build up in the liver. If this buildup is due to alcohol consumption, it is called alcoholic fatty liver disease. When alcohol is not a causative factor, the buildup of fat in the liver is called nonalcoholic fatty liver disease (NAFLD).
People with metabolic syndrome are at a higher risk of NAFLD. Fatty liver disease may sometimes cause tiredness and pain on the right side of the abdomen, but it often causes no symptoms. A doctor may test someone with alcohol use disorder or metabolic syndrome for elevated liver enzymes to check for fatty liver disease.
Hepatitis
Hepatitis is a virus that leads to liver inflammation. There are several different strains of hepatitis, which are called A, B, C, D, and E. The symptoms of all of the strains are similar.
Common hepatitis symptoms include:
- fatigue
- muscle soreness
- joint pain
- nausea
- loss of appetite
- stomach pain
- fever
- dark urine
- skin itching
- yellowing of the eyes and skin (jaundice)
Testing for elevated liver enzymes
Blood test can show elevated liver enzymes. The blood test checks for raised levels of AST and ALT, which are enzymes that the liver releases when it becomes inflamed or damaged.
If a doctor finds that a person has raised AST or ALT levels, they are likely to carry out further tests to determine the underlying cause.
Different ratios of AST to ALT may indicate various underlying causes.