Liver numbers a little high at my health check: what first?

If ALT or AST came back a little high at your health check, start by taking the whole report to a doctor and telling them what your week before the test looked like. MedlinePlus, from the US National Library of Medicine, says a high ALT does not always mean a health problem: age, sex, weight, intense exercise, certain medicines and dietary supplements can all affect the result, and the doctor compares it with your other liver results. You are not alone either. In the annual health checks of Royal Thai Army personnel, at least a quarter had an ALT of 37 U/L or more in every year from 2017 to 2021.

What does a "high" ALT or AST on my report mean?

ALT and AST are the two values most people mean when they say "liver numbers". They usually sit in a group of liver results on the report, next to values such as GGT, ALP and bilirubin.

What the two values are

MedlinePlus explains that ALT and AST are enzymes, proteins that speed up chemical reactions in the body. ALT is found mainly in the liver. AST is found mainly in the liver too, but also in the heart, muscles and other tissues. Usually only low levels are in the blood; when cells that contain them are damaged, more is released into the blood. For what each liver value on the report looks at, see What do ALT, AST and GGT on my health check mean?

Why one high number is not the whole picture

The MedlinePlus page on liver function tests says these tests on their own usually cannot tell the exact cause of a result, so a doctor compares all the liver values together, looks for patterns and may order other tests. The doctor also considers your symptoms, history and the medicines you take. An "H" next to ALT is a reason to talk to a doctor, not a reason to panic.

The mark for "high" differs between labs

Each lab prints its own reference range next to your result. The army study, for example, counted ALT or AST as high from 40 U/L in men and 35 U/L in women. A 2017 US guideline for doctors by Kwo and colleagues puts a truly healthy ALT lower, at 29 to 33 U/L for men and 19 to 25 U/L for women. So the same number can be flagged at one clinic and not at another. Ask the doctor which range your report uses.

Is a slightly high liver number common in Thailand?

In some groups of Thai adults, yes. Large health check records give a picture of how often it happens.

What army health checks show

Sakboonyarat and colleagues at Phramongkutklao College of Medicine analysed the annual health check records of 244,281 active-duty Royal Thai Army personnel aged 35 to 60 from 2017 to 2021. About 90% were men, the average age was 47 to 48, and about two thirds said they currently drank alcohol.

In 2017, a quarter of the results were 44 U/L or more, above the 40 U/L mark the study used for men.

What a village study in the north found

A 2026 study from the University of Phayao's School of Public Health measured ALT in 405 randomly selected adults aged 20 and over in rural Phayao. Higher scores on a standard drinking questionnaire (AUDIT) went with higher ALT in both women and men.

What these numbers can and cannot tell you

The army group is mostly middle-aged men, and the Phayao study covered one province, so neither describes all Thai adults. Both looked at each person at one point in time. They show that a slightly high ALT is a common finding, but they cannot tell you what your own result means; that is the doctor's job.

What can push ALT and AST up before a test?

Several everyday things can move these values for days or weeks. Knowing them helps you tell the doctor what matters.

Hard exercise

In a 2008 Swedish study by Pettersson and colleagues, 15 healthy men who were used to moderate activity, but not to weightlifting, did one hour of weightlifting. Their AST and ALT rose and stayed raised for at least 7 days, while GGT, ALP and bilirubin stayed within the normal range. It was a small study of men only, but it shows why a hard gym session in the week before a check is worth mentioning.

A recent illness

MedlinePlus notes that if you have been ill recently, some abnormal liver results may be temporary, and the provider may repeat the tests later to see whether they return to normal.

A few weeks of very heavy eating

In a 2008 Swedish study by Kechagias and colleagues, 18 healthy young adults ate at least two fast-food meals a day, aiming to double their usual calories, and moved little for 4 weeks. Average ALT went from 22.1 U/L at the start to an average personal peak of 97 U/L, and 11 of the 18 stayed above the reference limits during the study. It was a small study of 18 young, healthy Swedish adults who deliberately overate for a short period, and it looked only at that period of overeating. The authors concluded that when ALT is high, doctors should ask not only about alcohol but also about recent heavy eating. If you have just come back from a holiday of big meals, or have been eating much more than usual, say so.

Alcohol, medicines and supplements

MedlinePlus lists alcohol among the things that can raise AST, and certain medicines and dietary supplements among the things that can affect ALT. The US guideline asks doctors to check both prescribed and over-the-counter medicines.

At a glance

What should I do first?

Three simple steps help the doctor read your result accurately.

Step 1: take the whole report to a doctor

Bring this report and any earlier ones. ALT and AST make sense next to your other liver values and your history, and earlier results show whether today's number is new.

Step 2: write down your week before the test

• any hard exercise, sport or physical work, and on which days
• any illness, fever or upset stomach in the weeks before
• whether you had been eating much more than usual
• how much you drank, counted in drinks per week
• every medicine, vitamin, supplement and herbal product you take
• whether your weight has changed over the past few years

Step 3: ask about a repeat test and how to prepare

Ask whether and when to test again. The MedlinePlus page on fasting for a blood test says that while fasting you should not chew gum, smoke or exercise, that you may be asked not to drink alcohol for a longer period, and that you can usually drink plain water. Follow the clinic's own instructions.

For preparing before a health check in general, see My health check is coming up again. What should I change? If several values on your report changed at once, see Weight went up and my check-up got worse. Where to start?

What general guidance applies to all adults?

The guidance below is general advice for all adults, not specific advice about liver numbers.

Alcohol

The NHS advises men and women not to regularly drink more than 14 units a week. Using the NHS formula, a large 620 ml bottle of 5% beer is about 3.1 units, so four and a half large bottles already reach 14 units. For counting drinks and drink-free days, see I drink alcohol often. What should I know about blood fats?

Physical activity

The World Health Organization advises adults to do 150 to 300 minutes of moderate-intensity activity, such as brisk walking, or 75 to 150 minutes of vigorous activity a week, plus muscle-strengthening on 2 or more days.

When should I see a doctor sooner?

If you notice any of the signs below, see a doctor promptly instead of waiting for the next health check.

Signs to see a doctor promptly

MedlinePlus lists these as signs for which liver tests may be needed:

• skin or the whites of the eyes turning yellow
• dark urine or pale stools
• swelling or pain in the belly, or swelling in the ankles and legs
• nausea and vomiting, loss of appetite, or itching that keeps coming back

About medicines

Do not start, stop or change regular medicines or supplements on your own because of this result. Ask the doctor or pharmacist first.