ALT (Alanine Aminotransferase) Blood Test

An ALT blood test measures an enzyme mostly found in the liver, and it's often used to check for liver damage or disease. High ALT levels can point to liver stress, while low levels are usually not a health concern.

ALT, also known as SGPT, is an enzyme found mainly inside liver cells, with smaller amounts in the kidneys, heart, and muscles. It helps the body break down amino acids and convert nutrients into usable energy. When liver cells are healthy, most ALT stays inside them, so blood levels are normally low. If liver cells become damaged, injured, or die, ALT can leak out into the bloodstream, and a blood test measures how much is circulating. Because ALT is fairly specific to the liver compared with many other enzymes, it is often used as a key marker of liver cell health. Doctors often look at ALT alongside AST to get a fuller picture of liver function.

ALT is commonly ordered as part of routine health checkups, before starting certain medications, or when someone has symptoms that could relate to the liver, such as fatigue, nausea, abdominal discomfort, or yellowing of the skin or eyes. It is included in the comprehensive metabolic panel (CMP) and in dedicated liver panels, often measured together with AST, ALP, GGT, and total bilirubin. Clinicians may also track ALT over time to monitor known liver conditions, check for medication side effects, or follow up on earlier abnormal results.

ALT results are reported in units per liter (U/L) and are compared with a reference range set by the testing laboratory. Reference ranges can differ slightly between labs and may vary by sex, so it's helpful to check the range printed on the actual lab report rather than relying on general figures found elsewhere.

A high ALT result can occur for many reasons and does not by itself point to a specific liver condition. Some common contributors include fatty liver disease, which can be linked to excess body weight, insulin resistance, or metabolic syndrome. Heavy or frequent alcohol use can also raise ALT levels over time. Certain medications, including some cholesterol-lowering drugs, pain relievers, and antibiotics, may affect liver enzymes, as can some herbal or dietary supplements. Viral infections such as hepatitis A, B, or C can cause temporary or ongoing elevations, and other less common causes include autoimmune liver disease, bile duct blockage, and certain metabolic or genetic liver disorders. Intense exercise or muscle injury can sometimes raise ALT slightly as well, since small amounts of the enzyme exist outside the liver. Because so many factors can influence ALT, an elevated result usually calls for additional testing, a review of medications and health history, and follow-up with a healthcare provider rather than assuming a single cause. Repeat testing may help clarify whether an elevation is temporary or persistent.

Low ALT levels are less often a focus of concern and usually do not indicate a health problem on their own. In many cases, a low result simply reflects where a person's usual ALT sits within the reference range. Some research has looked at whether very low ALT might relate to vitamin B6 deficiency, since this vitamin is needed for the enzyme to work properly, though this connection is still being studied. Advanced liver disease can sometimes show unexpectedly low ALT alongside other abnormal liver markers, so context matters. General frailty, significant muscle loss, or certain chronic illnesses have also been associated with lower-than-average ALT readings in some studies. Because low ALT is rarely evaluated in isolation, it is typically interpreted together with other liver panel results, symptoms, and overall health history rather than as a standalone finding.

ALT is often reviewed together with related markers such as AST, ALP, GGT, total bilirubin, and albumin to build a broader picture of liver health, since each marker reflects a different aspect of liver function or injury. The ratio between ALT and AST can sometimes offer additional clues, though it is only one piece of a larger clinical picture. Lifestyle factors such as alcohol use, body weight, diet, and physical activity can all influence ALT levels, as can many prescription and over-the-counter medications and supplements. Because reference ranges and testing methods can vary between laboratories, it's important to compare results with the range listed on the specific lab report rather than a general guideline found online.

If an ALT result falls outside the expected range, a healthcare provider can help interpret it alongside other liver panel markers, medical history, and any symptoms. It may be helpful to mention current medications, supplements, alcohol use, and recent illnesses when discussing results. Repeat testing or additional liver studies are sometimes recommended to see whether a change is temporary or ongoing. Urgent: Severe abdominal pain, confusion, vomiting blood, or yellowing of the skin or eyes may require immediate medical attention—contact a healthcare provider right away or seek emergency care. Uploading a lab report to MediWing can offer a plain-language explanation of results and help track trends over time.