ALT value: how to read your result

ALT stands for alanine aminotransferase. Older reports call it SGPT and Dutch reports ALAT; it is the same enzyme every time. It helps liver cells process protein and is supposed to stay inside those cells. The test counts how much of it is floating around in your blood, in units per litre.

A small amount of ALT in the blood is normal, because liver cells renew themselves all the time. The number climbs as soon as more cells than usual break down at once. The higher the value, the more cells are damaged, but the number says nothing about the cause. For that, a doctor looks at the other values on the same form.

The most important of those is AST, which also comes from muscle and red blood cells. If both are raised and AST the most, a doctor thinks of muscle work before the liver. Gamma-GT points towards alcohol or the bile ducts, and CK is the enzyme that comes almost only from muscle. With those three beside it, your ALT number can be placed at a glance.

Say your ALT is 52. That is mildly raised: a little over the limit of 45 for men, and one and a half times the limit of 34 for women. These are, from most to least likely, the explanations a GP then works through.

One: you exercised hard shortly before the draw. A heavy workout, a long bike ride or a first strength session raises ALT for a few days, and AST even more. Two: fatty liver. This is the most common cause of a mildly raised ALT in the Netherlands, causes no symptoms, and goes with abdominal fat, little exercise and a high blood sugar. Three: alcohol. A few glasses a day is enough to push the value up, usually together with a raised gamma-GT. Four: a medicine or supplement. High-dose paracetamol, some antibiotics, statins, and supplements such as high-dose green tea extract, ashwagandha and curcumin all appear in reports of liver injury. Five: a viral infection. Glandular fever or a hepatitis virus usually gives much higher values, often several times the upper limit, and then you feel ill as well.

If the value is still raised on a repeat and none of those five explains it, a doctor looks further: at your iron values, your thyroid, at coeliac disease and at hepatitis B and C. That is not a panic step but the normal order of things. What a mildly raised ALT almost never means is that your liver is seriously ill right now; for that you see very different numbers. What you can do with a raised result is set out step by step in ALT value: normal values and what abnormalities mean for your liver.

You do not need to request ALT separately: it is in almost every standard blood test and every liver package. If you specifically want to know how your liver is doing, for example because you drink regularly, have started a new medicine or want to check an earlier result, choose a panel that also includes AST, gamma-GT and CK. On its own an ALT number is hard to read; alongside those three it is not.

Fasting is not needed for ALT. What does count is what you did in the days before. Skip heavy exercise for two to three days before the draw, and after an unusually hard effort preferably a week, or you will be measuring your muscles instead of your liver. An evening of heavy drinking shortly before the draw can also lift the value temporarily.

Was your previous result mildly raised? Repeat the measurement after three to four quiet weeks. If the value drops, it was a snapshot. If it stays the same or rises, that is the moment to discuss it with your GP.