Raised liver values: what do ALT and AST mean?

What liver enzymes actually measure

ALT and AST sit inside your liver cells. If those cells are damaged or irritated, some of those enzymes leak into your blood. That is what a laboratory measures.

An important detail: this says something about cell damage, not about how well your liver is doing its job. Your liver can work perfectly well while these values are raised, and conversely, normal enzymes do not tell you everything about the function itself.

How well your liver does its work is better reflected by albumin, bilirubin and clotting. Those therefore belong to a complete liver assessment.

ALT sits almost exclusively in the liver and is the more specific of the two. AST also occurs in muscle, heart and red blood cells. That difference explains many confusing results.

The values that build the picture together

A single raised value is hard to interpret. The combination shows where the problem sits:

If ALT and AST stand out together, that points towards the liver cell itself. If GGT and alkaline phosphatase lead, attention shifts towards the bile ducts.

What is a normal ALT or AST value?

ALT is short for alanine aminotransferase, AST for aspartate aminotransferase. Search for a normal ALT or AST value and you will find tables that all differ slightly. That is not sloppiness: what counts as normal depends on the laboratory analysing your blood. Laboratories use different measuring methods and set their reference ranges accordingly, often separately for men and women.

That is why we deliberately do not publish thresholds of our own. Your report always shows your value next to the reference range of the performing laboratory, and that range is leading. There is also a real difference between mildly and strongly raised: a value just above the upper limit often has an everyday explanation, while a multiple of the upper limit calls for quicker interpretation. Our doctor addresses that distinction in the explanation with your report.

Common causes of a rise

These are the explanations that come up most often:

• Fatty liver, often linked to excess weight, a raised blood sugar or unfavourable blood lipids. This is the most common cause.
• Alcohol, with GGT and AST responding in particular.
• Medication and supplements, from paracetamol in overdose to certain antibiotics, cholesterol-lowering drugs and herbal preparations.
• A viral infection, such as hepatitis A, B or C, but also glandular fever.
• Heavy physical exertion, where muscle contributes to the AST.
• More rarely: autoimmune hepatitis, iron overload or a gallstone blocking the outflow.

With a mild rise and no symptoms, fatty liver is statistically the first candidate. That is no reason to panic, but it is a signal worth attention, because it is connected to your metabolism.

Why exercise can distort your result

This is often overlooked. After heavy strength training, a marathon or unusual exertion, muscle cells leak enzymes into your blood, including AST and to a lesser extent ALT.

Your liver has nothing to do with it, but the result suggests otherwise. If you want a clean picture, leave at least two to three days of rest between a hard session and the blood draw.

If creatine kinase is measured at the same time, that is often the key. If it is markedly raised, the pattern points to muscle rather than liver.

What happens after an abnormal result

A raised liver value is a starting point, not an end point. The usual sequence looks like this:

1. 1Check what was going on around the draw: alcohol, an infection, new medication, supplements or heavy exercise.
2. 2Repeat the value after a few weeks, together with GGT, alkaline phosphatase, bilirubin and albumin.
3. 3If the rise persists, your GP arranges further testing, often an abdominal ultrasound and targeted blood tests for viral hepatitis or iron overload.
4. 4Based on that, it is decided whether referral to a specialist is useful.

What you can do between two measurements: limit or pause alcohol and look critically at your supplements. Never stop prescribed medicines on your own initiative.

Who is testing useful for?

Having liver values measured mainly makes sense when there is a concrete reason:

• you drink alcohol regularly and want to know what it does
• you carry excess weight, have a raised blood sugar or unfavourable blood lipids
• you use long-term medication known to burden the liver
• you want to follow a previously found abnormality over time
• you have symptoms such as persistent fatigue or pressure in the upper right abdomen

Without a reason, a single liver value mainly produces worry. A slightly abnormal result occurs regularly in people who are perfectly healthy.

If you combine liver values with other tests, the picture becomes usable much faster. A raised ALT alongside a high blood sugar and unfavourable blood lipids tells a different story than the same value in someone who has just had a viral infection or ran a half marathon last week.

Having your liver values tested at Bloodworks

At Bloodworks you have liver values measured without a referral, at one of the more than 1000 affiliated collection points across the Netherlands. If you only want the two enzymes, the individual ALT and AST test is enough.

If you want a complete picture, the Liver function package measures six values in one draw: albumin, ALT, AST, GGT, alkaline phosphatase and total bilirubin. Your result is reviewed by a doctor and reaches you as a personal PDF report, typically within 2 working days.