Alanine Aminotransferase (ALT)
ALT is the liver enzyme that leaks into your blood when liver cells are stressed or damaged. A result inside the range on your report is reassuring. A raised result is a signal your liver deserves a closer look, though many mild rises turn out to be temporary. Your GP weighs it against your medications, lifestyle and other liver markers before drawing any conclusions.
Standard CareWhat is alanine aminotransferase (alt)?
Alanine aminotransferase (ALT) is an enzyme — a protein that speeds up chemical reactions — found mainly in liver cells. In healthy liver tissue, ALT stays inside the cells; when those cells are damaged or stressed, they release ALT into the bloodstream where it can be picked up in a blood test. Because ALT lives predominantly in the liver (with smaller amounts in the kidneys, heart, and muscles), a raised blood ALT level is considered one of the more useful pointers towards possible liver injury, which your GP interprets alongside your other markers. ALT is not measured in isolation. It is one of the Liver Function Tests (LFTs) — a standard group of blood markers that your doctor orders together to build a picture of liver health. The other markers in the panel include AST (aspartate aminotransferase — a related enzyme also released when liver cells are damaged), GGT (gamma-glutamyl transferase — sensitive to alcohol and bile-duct stress), ALP (alkaline phosphatase — often raised with bile-duct or bone problems), albumin (a protein the liver makes), and bilirubin (a yellow pigment processed by the liver). Reading ALT alongside these companions is what lets your GP separate the different patterns of liver stress.
Why is it tested?
Your GP may order an ALT test — usually as part of a full LFT panel — for several reasons. Most often it is to check general liver health during a routine screen, or to look into symptoms such as jaundice (a yellowing of the skin or whites of the eyes), lasting fatigue, nausea, or discomfort on the right side of the abdomen. It is also used to keep an eye on the liver while you take medications known to affect it, such as statins for cholesterol or paracetamol at higher doses. And it helps assess a known or suspected liver condition — viral hepatitis (liver inflammation caused by hepatitis A, B, or C viruses), fatty liver disease (where fat builds up in liver cells), or alcohol-related liver disease — or simply to track liver health over time after an earlier raised result. ALT is also more specific to the liver than AST (both are transaminases, the liver-released enzymes), which makes it a particularly useful early signal of injury to the main liver cells (the hepatocytes).
Reference range (Australia)
ALT reference intervals are assay-dependent and vary between Australian laboratories — the range printed on your own report is the authoritative figure for your result. As a guide, Australian studies and laboratories have used upper limits of approximately 40 U/L in men and 30 U/L in women, reflecting the fact that men tend to have slightly higher ALT levels at baseline. A result above your lab's reference interval warrants discussion with your GP.
Reference intervals vary between laboratories. Always use the range printed on your own report.
What your result means
A low ALT result is rarely a concern. In most cases it reflects normal individual variation, differences between laboratory assays, or simply that liver cells are not under stress. Your GP will focus on the overall LFT pattern and your clinical picture rather than a low ALT reading on its own.
An in-range ALT result suggests your liver cells are not releasing significant amounts of the enzyme, generally a reassuring sign, and for most people that is exactly what it means. One nuance worth knowing: in long-standing liver disease such as cirrhosis (scarring of the liver tissue), ALT can sometimes read normal because fewer cells remain to release it, which is why your GP reads it alongside the rest of the panel and your overall picture rather than on its own.
A raised ALT means liver cells have been releasing the enzyme into your blood — a sign of hepatocellular injury (damage or stress to the main liver cells). The cause can range from very common and manageable to less common conditions that need investigation. The most common reason is fatty liver disease — known medically as metabolic dysfunction-associated steatotic liver disease (MASLD, previously NAFLD), where fat builds up in liver cells. Alcohol-related stress and viral hepatitis (liver inflammation caused by hepatitis A, B, or C viruses) are also frequent. Many medicines can raise ALT for a while too (see "What affects it?"). Other metabolic conditions, including obesity and type 2 diabetes, can play a part as well. A mildly raised ALT is very common, and a single result does not point to a specific diagnosis. Your GP will consider how high the number is, whether it is rising or falling on repeat testing, your medications, alcohol intake, weight, and any symptoms — before deciding whether to investigate further or simply monitor. Many mild, transient elevations settle on their own.
What can affect your result
A wide range of medications can raise ALT. Statins (cholesterol-lowering medicines) commonly cause a mild, transient rise; the Australian Prescriber guidance notes that many patients on statins have a mild transient elevation of liver enzymes which is of no clinical consequence, while a persistent moderate rise may point to underlying fatty liver rather than the medication itself. Beyond statins, a number of other medicines can nudge ALT up for a time, including some used for heart rhythm, certain antidepressants, some drugs for inflammatory conditions, some antibiotics, and a range of herbal supplements. If you take regular medicines, it is worth your GP reading your result with your medication list in front of them. Beyond medications, a few lifestyle and health factors matter most. Alcohol is a big one — even modest amounts can lift ALT for a time, and alcohol-related liver disease is a major cause of a lasting rise. Excess body weight is another, closely tied to fatty liver disease, the most common liver condition in Australia. Type 2 diabetes and metabolic syndrome (a cluster including raised blood sugar and insulin resistance) also affect how the liver handles fat. And viral infections such as hepatitis A, B, and C injure liver cells directly. The AST:ALT ratio — comparing the levels of these two related enzymes — can help distinguish between patterns. Usually ALT is higher than AST; if alcohol is the primary driver, the ratio can reverse, with AST more than twice the level of ALT.
When to act
If your ALT is raised, that is worth a conversation with your GP rather than something to act on alone. They will look at how far the number sits above the reference interval on your report, whether a repeat test shows the same pattern, and how it compares with the other markers on your LFT panel — particularly AST, GGT, ALP, albumin, and bilirubin. They will also ask about your medications, alcohol intake, diet, weight, and any symptoms. Depending on the pattern and context, your GP may recommend watching and waiting with a repeat test in a few weeks, adjusting or pausing a medication, organising an ultrasound of the liver, or referring you to a gastroenterologist or hepatologist (liver specialist) for further assessment. If you have a raised ALT alongside jaundice (yellowing of the skin or eyes), persistent fatigue, nausea, dark urine, or right-sided abdominal pain, it is worth telling your GP without delay, as that combination is one they will want to look at sooner. This page is general information and is not a substitute for advice from your GP.
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