Alanine aminotransferase, commonly known as ALT, is an enzyme found predominantly within liver cells. While smaller amounts exist in other tissues like the kidneys, heart, and muscles, ALT is a specific indicator of liver health. This enzyme aids metabolism by helping the liver break down proteins. Elevated ALT levels in the bloodstream often signal damaged or inflamed liver cells, which release the enzyme.
Defining Normal ALT Levels
A blood test measures ALT levels to assess liver function. The typical normal range for ALT generally falls between 7 and 56 units per liter (U/L), though this can vary slightly depending on the specific laboratory and its testing methods. Some sources provide more specific ranges, such as 7 to 55 U/L for males and 7 to 45 U/L for females.
Several factors can influence an individual’s ALT range. Men often have higher levels than women, and younger individuals tend to have higher levels than older adults. Body mass index (BMI) can also play a role, with obesity correlating with higher readings. Certain medications, including over-the-counter pain relievers like acetaminophen, and intense physical exercise can temporarily increase ALT levels. Slight variations within or just outside the established normal range do not always indicate a serious condition but warrant medical review.
Implications of Abnormal ALT Levels
Elevated ALT levels often suggest liver damage or inflammation. Common causes include fatty liver disease, which can be alcohol-related or non-alcoholic (MASLD), and various forms of hepatitis. Certain medications, excessive alcohol consumption, heart failure, or too much iron in the body (hemochromatosis) can also lead to increased ALT. In some cases, high ALT may stem from muscle damage, as a small amount of the enzyme is found in muscle cells.
Unusually low ALT levels are less common and generally not a cause for concern. However, consistently low levels might sometimes be linked to a vitamin B6 deficiency, as this vitamin is needed for ALT to function properly. Chronic kidney disease or malnutrition can also be associated with lower ALT readings. An abnormal ALT result is not a definitive diagnosis on its own; instead, it serves as an indicator that further investigation by a healthcare professional is necessary to determine the underlying cause.