Liver function tests or LFTs are blood tests designed to determine how well your liver is working. The concentrations of several liver enzymes in your blood, including alanine aminotransferase, serve as good indicators of liver damage. High levels of alanine aminotransferase usually indicate a damaged liver. However, low levels may also be problematic and should be further correlated with other clinical data.
Your body uses the enzyme alanine aminotransferase to transfer amino, or NH2 groups, from one molecule to another. Alanine aminotransferase degrades the amino acid alanine into fuel for your cells. Degradation of alanine forms a molecule called pyruvate. Pyruvate can then either be turned into energy for your cells immediately or turned back into glucose and stored as fat. Other names for alanine amino transferase include serum glutamic pyruvic transaminase and alanine transaminase or just plain ALT. Most of the activity of alanine aminotransferase takes place in your liver.
When damage occurs to a specific organ in your body or that organ does not function properly, cells die. When cells die, they release their contents into the surrounding blood. Because your liver contains high concentrations of ALT when working properly, liver damage causes the release of high concentrations of ALT into your bloodstream. The severity of the liver damage, however, does not necessarily correlate with the concentration of ALT in your blood, as the test measures only the amount of ALT in your bloodstream at a given point in time. The normal range for ALT falls between 5 IU/L to 60 IU/L, where IU/L stands for International Units per liter.
Low ALT Levels
While most low ALT level results indicate a normal healthy liver, that may not always be the case. A low-functioning or non-functioning liver, lacking normal levels of ALT activity to begin with, would not release a lot of ALT into the blood when damaged. People infected with the hepatitis C virus initially show high ALT levels in their blood, but these levels fall over time. Because the ALT test measures ALT levels at only one point in time, people with chronic hepatitis C infection may already have experienced the ALT peak well before blood was drawn for the ALT test. Urinary tract infections or malnutrition may also cause low blood ALT levels.
High ALT Levels
High ALT levels usually represent liver damage, which may be from viral hepatitis, autoimmune hepatitis, excessive alcohol consumption, alcoholic liver disease, inflammation of the liver due to medication or herbal supplements, or various other liver diseases or liver tumors. In addition, heart failure can also raise ALT levels. ALT levels can be higher in people with obesity. If you take over-the-counter pain medications such as acetaminophen, or if you have celiac disease, Epstein-Barr virus, mononucleosis, muscular dystrophy, pancreatitis, gallbladder inflammation, or Wilson's disease, your ALT levels might also be higher than normal.
Specific ALT Levels
Elevated ALT levels may not necessarily correlate with disease, but clinicians can make some general predictions based on where a patient's serum level is with respect to the reference range of ALT. Slightly elevated ALT levels, those above 50 IU/L but below 300 IU/L, can indicate any kind of liver disease, or may just be a normal level for that particular person. Levels of 1,000 IU/L or above, however, indicate liver damage from drugs, toxins, viral hepatitis or a lack of oxygen to the liver due to a heart attack, for example. Bile duct blockage is suspected if this high level resolves within 24 to 48 hours. Moderately high ALT levels between 300 IU/L and 1,000 IU/L indicate acute or chronic hepatitis.