ALT value: what this liver enzyme measures

The test measures how much ALT is circulating in your blood. The result is given in units per litre, abbreviated u/l. ALT stands for alanine aminotransferase.

Older reports sometimes carry the former name SGPT. It is the same enzyme and the same measurement.

The enzyme works inside the cell. It moves an amino group between two compounds. Your body needs that step to convert amino acids into fuel.

As long as a cell is intact, the enzyme stays inside it. Only when liver cells are damaged does ALT leak out.

Where ALT sits determines what the result is worth. The enzyme is concentrated mainly in the liver, far more than anywhere else. Small amounts sit in kidney, heart and skeletal muscle. That distribution makes ALT more liver-specific than AST, which occurs in many tissues at once.

This is why ALT rarely appears alone on a report. You usually see it beside AST, gamma-GT, alkaline phosphatase and bilirubin. Each enzyme points in a different direction.

ALT and AST come from the liver cell itself. Gamma-GT and alkaline phosphatase come from the bile ducts. That split guides the further investigation a doctor chooses.

The measurement itself says nothing about the cause. It only adds up how much enzyme is circulating. What a high ALT value means becomes clear only alongside the other liver values.

A raised ALT value means liver cells are being damaged. It is not a diagnosis. It is a signal that something deserves attention.

The order of likelihood matters more here than the list itself. In the Netherlands, fatty liver is by far the most common reason for a mildly raised result. That rise usually stays modest, roughly one to three times the upper limit. It also fluctuates between draws.

Medicines and supplements come next. Paracetamol in overdose counts, as do amoxicillin with clavulanic acid and anti-epileptics. Among supplements the usual names are green tea extract, ashwagandha and high-dose curcumin. Heavy alcohol use sits in the same category, though alcohol typically shifts the ratio with AST the other way.

Viral hepatitis produces the strongly raised results. In acute viral hepatitis, ALT climbs to many times the upper limit. Hepatitis B and hepatitis C are established with serology, not with this enzyme. ALT only shows that something is going on.

There is a second reason this result counts, and it is often missed. The reference limit is derived from the average population, not from healthy people. Work in screened blood donors arrived at a healthy upper limit near 30 u/l for men and near 19 u/l for women.

The 45 and 34 on your report are therefore a laboratory limit. A woman with a value of 30 reads "normal" and sits well above that healthy limit. This is not a reason to worry, but it is a reason to talk when metabolic risk factors are present.

Conversely, a normal ALT value does not rule fatty liver out. A large share of people with proven fatty liver have enzymes inside the reference range.

ALT is a standard part of a liver panel. Such a panel is requested for symptoms that could fit the liver. It is also routine when monitoring medicines that burden the liver. And it belongs in a broader health check.

One preparation rule genuinely matters. Do no heavy or unaccustomed training in the 48 to 72 hours beforehand. Muscular effort lifts ALT less than AST, but noticeably. Anyone who has just started a new programme should wait a little longer.

Repeating says more than any single snapshot. Enzyme values fluctuate from week to week. The direction a value moves in is more informative than the isolated number.

If a raised ALT value is found, a second ALT rarely follows. The logical next step is the context around it: AST, gamma-GT, alkaline phosphatase and bilirubin. If the value stays raised, a search for the cause belongs with it. That means serology for hepatitis B and C, iron status, and a metabolic assessment.

Always discuss abnormal ALT values with your GP. Even when you already suspect an explanation yourself.