ALT (Alanine Aminotransferase): Normal Range, What High & Low Levels Mean

ALT stands for alanine aminotransferase, an enzyme found mainly inside your liver cells. You may also see it labelled SGPT or serum glutamic pyruvic transaminase on older lab reports — they all refer to the same thing. Under normal circumstances, very little ALT escapes into your bloodstream. When liver cells are damaged or inflamed, they release ALT, and your blood test picks up that rise. This makes ALT the most specific blood marker doctors have for detecting liver injury early. It gives a window into liver health that's hard to spot any other way without imaging. Discuss your specific ALT result with your healthcare provider to understand what it means for you personally.

According to Mayo Clinic Laboratories, the standard reference range for ALT in adult males aged 18 and over is 7 to 56 U/L (units per litre). For adult females aged 18 and over, the range is slightly lower, sitting between 7 and 45 U/L. These ranges reflect values seen in the majority of healthy adults and are used as a benchmark when interpreting your result. Keep in mind that reference ranges can vary slightly between laboratories depending on the equipment and methods they use, so the range printed on your own lab report is the most relevant one to read alongside your number. Your healthcare provider is best placed to explain whether your specific result falls where it should.

A high ALT level means more of the enzyme has leaked out of liver cells into your blood than usual, which points to some degree of liver cell stress or damage. There are many possible causes. The most common reason for a mildly elevated ALT in developed countries is nonalcoholic fatty liver disease (NAFLD), a condition where excess fat builds up in the liver. Other causes include alcoholic liver disease, viral hepatitis A, B, or C, autoimmune hepatitis, drug-induced liver injury from medicines like statins, acetaminophen, or certain antibiotics, celiac disease, thyroid disorders such as hypothyroidism, strenuous exercise, liver cirrhosis, and a condition called hemochromatosis. A single raised result does not diagnose any of these on its own. Please discuss your result with your healthcare provider for proper evaluation.

A low ALT result — one that falls below the reference range — is generally not considered clinically significant on its own. Because ALT is an enzyme that requires vitamin B6 as a cofactor to function, a deficiency in that vitamin can reduce measured levels. In people with chronic kidney disease who are on dialysis, muscle wasting over time can also lower ALT. Interestingly, regular long-term aerobic exercise training has also been associated with lower ALT readings. In most cases, a low ALT is not a sign of a problem, but rather a reflection of individual factors like body composition or nutritional status. Your healthcare provider can help you understand whether your low result needs any follow-up in the context of your full health picture.

When ALT is only mildly elevated, many people experience no symptoms at all — which is one reason routine blood tests are so valuable. If the liver is under greater stress, you might notice fatigue and a general loss of energy, nausea or a reduced appetite, or a dull pain or discomfort in the upper right side of your abdomen. In more serious cases, jaundice — a yellowing of the skin or the whites of the eyes — can develop, along with dark-coloured urine, pale stools, and itchy skin. On the other side, a low ALT level typically causes no symptoms whatsoever. If you are experiencing any of these symptoms alongside an abnormal result, discuss them with your healthcare provider as soon as possible so they can investigate further.

A result just outside the reference range doesn't automatically mean something is seriously wrong. Lab reference ranges represent the middle band of results seen in most healthy adults, so a small deviation can sometimes reflect everyday factors like recent vigorous exercise, a new medication, or natural variation between laboratories. What matters most is the pattern over time, how far outside the range your result sits, and how it fits alongside your other test results, symptoms, and medical history. Doctors rarely act on a single isolated reading without looking at the broader picture. Tracking your ALT over time — something Serumo can help you do — gives you and your doctor much more useful information. Always bring your results to your healthcare provider to get a personalised interpretation.