AST (Aspartate Aminotransferase): Normal Range, What High & Low Levels Mean

AST stands for aspartate aminotransferase, an enzyme produced by cells in your liver, heart, muscles, kidneys, and red blood cells. Under normal conditions, very little of it circulates in your bloodstream. When any of those cells are damaged or inflamed, they release AST, so the test measures how much has spilled into your blood. Doctors use it most often alongside ALT to get a clearer picture of liver health, though a high result can also point to problems in the heart or muscles. Talk to your healthcare provider about what your specific AST result means in the context of your full lab panel.

According to Mayo Clinic Laboratories, the reference range for AST is 10 to 40 U/L for adult males aged 18 and older, and 10 to 35 U/L for adult females aged 18 and older. U/L means units per liter of blood. These ranges represent where most healthy adults fall, but labs can differ slightly in the cutoffs they use, so always compare your result to the range printed on your own lab report. A number inside this window generally suggests there is no major cell damage releasing AST into your blood. Discuss your exact result with your healthcare provider to understand what it means for you personally.

Several conditions can push AST above the normal range. The most common include liver diseases such as hepatitis, cirrhosis, non-alcoholic fatty liver disease, and alcoholic liver disease. A heart attack can cause a significant spike because damaged heart muscle releases AST. Strenuous exercise or muscle injuries, drug-induced liver injury from medications like acetaminophen or statins, hemolytic anemia — where red blood cells break down rapidly — pancreatitis, thyroid disease, and celiac disease can all raise AST as well. Because so many different conditions share this marker, a high result alone cannot tell you which one is responsible. Your healthcare provider can order follow-up tests to find the cause.

A low AST result is generally not considered clinically significant — in most cases it simply means less enzyme has leaked into your bloodstream than the average, which is not harmful. That said, two situations can be associated with a low reading: a deficiency in vitamin B6, a nutrient your body needs as a building block to produce AST, and uremia, a complication of advanced kidney disease in which waste products accumulate in the blood. Neither of these is diagnosed from AST alone. If your result falls below the reference range or you have concerns about what a low number might mean for your health, bring it up with your healthcare provider.

A mildly elevated AST often produces no symptoms at all, which is why routine blood work can catch problems before you feel unwell. When a high AST is tied to liver stress, you might experience fatigue and weakness, nausea, loss of appetite, or a dull discomfort in the upper right side of your abdomen. More severe liver involvement can bring jaundice — a yellowing of the skin or eyes — and dark urine. If the elevation stems from a cardiac event, chest pain may be present. A low AST result typically causes no symptoms on its own. Symptoms are not always reliable guides to what your number means, so share any you are experiencing with your healthcare provider.

Whether you need a repeat AST test depends on how far outside the reference range your result falls, how it compares to your ALT and other liver markers, and your personal health history. Mild, isolated elevations sometimes resolve on their own — for example, after intense exercise or a short-term medication change — while persistent or significantly elevated levels usually warrant further investigation. Useful questions to bring to your appointment include: How does my AST compare to my ALT? Do I need imaging of my liver? Could any of my current medications be affecting this number? Has my result changed since my last test? Your healthcare provider is best positioned to guide your next steps based on your complete clinical picture.