Alanine aminotransferase (ALT): what your result means

The test measures how much ALT is circulating in your blood, expressed in units per litre (U/L). ALT stands for alanine aminotransferase. Older reports and some laboratories call the same enzyme SGPT.

Inside the liver cell the protein helps process nutrients. As long as the cell is healthy it stays there, and only a small amount reaches the blood. When liver cells break down, through inflammation, fat build-up, alcohol or a medicine, their contents are released and the ALT value climbs. That is why ALT is the most widely used blood value for detecting damage to liver cells.

Smaller amounts of ALT are also found in the kidneys and in skeletal muscle, which is why the value can rise a little after heavy exertion. AST, the enzyme almost always measured alongside ALT, comes from far more tissues: heart, muscle and red blood cells. When AST and ALT both rise but AST rises clearly more, the source is more likely to be muscle than liver.

A liver panel usually also carries gamma-GT and alkaline phosphatase. Those two come mainly from the bile ducts. If they stay normal while ALT rises, the problem sits in the liver cell itself. If gamma-GT rises with it, alcohol and bile flow come into the picture.

A mildly raised ALT is the earliest and often the only sign of fatty liver disease, the most common liver condition in the Netherlands. Fatty liver causes no symptoms for years. It also occurs in people who look lean and train a lot, because abdominal fat and insulin sensitivity weigh more heavily here than the number on the scale.

Strongly raised values, several times the upper limit, fit an acute inflammation of the liver, for example from a virus or a medicine. Paracetamol in too high a dose, some antibiotics and statins are known causes. Supplements can damage liver cells too: high-dose green tea extract, ashwagandha and curcumin preparations keep appearing in reports of liver injury. Anyone taking anabolic steroids by mouth runs a clearly higher risk.

For people who train a lot there is one more reason to know this value. A heavy or unaccustomed strength session raises ALT and AST for days. In a study of men who were not used to weightlifting, the values after a single session reached levels that resembled liver disease, and a week later they were still raised. Gamma-GT, alkaline phosphatase and bilirubin did not move in that study. That pattern, raised transaminases with normal bile-duct values, is exactly what separates muscle damage from liver damage. You can read more about that difference in high ALT and AST explained.

Have ALT measured if you want to know how your liver is doing, if you drink alcohol regularly, if you take medicines or supplements that burden the liver, or if you want to follow up an earlier abnormal result. The enzyme is part of almost every general blood test and of every liver panel.

Timing decides what you measure. Leave at least a week between a heavy or unaccustomed training session and the blood draw. After a first hard leg day, a new programme or a competition you need more recovery time; the end of a quiet week gives the cleanest picture. If you did train hard shortly before the draw, mention it when the result is assessed.

Ask for ALT together with AST, gamma-GT and creatine kinase (CK) where you can. With those three alongside, a raised value can be placed: muscle or liver, liver cell or bile duct. If the value is still raised on a repeat after about four weeks, training is no longer the explanation and further investigation through your GP is the right next step.