Alanine Transferase

ALT (Alanine Transferase, sometimes written ALAT) is an enzyme found almost exclusively inside liver cells. Because it is so liver-specific, it is widely regarded as the single most reliable marker for detecting stress or damage to liver tissue. When liver cells are healthy and intact, very little ALT leaks into the bloodstream. When they are irritated, inflamed, or dying, ALT spills out, and the blood level rises. This is why ALT is one of the first markers to move when something is putting pressure on your liver, often before you notice any symptoms.

A helpful way to picture ALT is to think of it as a warning light on a dashboard. Your liver is an extraordinarily busy organ, processing everything you eat, drink, and absorb, producing the proteins your body depends on, and filtering out toxins. Inside its cells, ALT plays a role in converting amino acids into glucose, a process called gluconeogenesis that helps keep your blood sugar steady between meals. As long as the cells stay intact, ALT does its work quietly. If the cell membrane is damaged, ALT escapes into the blood, and the level you see on your result rises accordingly.

ALT is sensitive to a broad range of common lifestyle factors. The most frequent causes of mildly raised ALT are non-alcoholic fatty liver disease (often linked to excess weight, insulin resistance, and a diet high in refined carbohydrates), alcohol above sensible limits, and certain medications, including statins, paracetamol at high doses, some antibiotics, and anti-epileptics. Supplements are an underappreciated contributor: high-dose vitamin A, green tea extract, kava, and some bodybuilding and weight-loss supplements are well documented to raise ALT. Viral hepatitis (A, B, C, E), autoimmune liver conditions, and muscle damage from very intense exercise can also push it up. ALT is usually interpreted alongside AST and GGT to clarify the source of the problem.

If your ALT is raised, your GP will consider the context, your alcohol intake, medications, supplements, weight changes, and other liver markers, before recommending next steps. Mild, stable elevations are often lifestyle-related and respond well to changes over a few weeks or months. Persistent or significant elevations may warrant further investigation, including a liver ultrasound or hepatitis screening.