ALT Levels Explained: What a High ALT Means

ALT, short for alanine aminotransferase, is an enzyme found mainly inside liver cells. When those cells are irritated or inflamed, more ALT leaks into the blood, so a raised ALT is one of the most common signs that the liver is under some strain. Older reports sometimes call it SGPT.

A high ALT is a frequent finding in people who feel completely well, and most mild rises have a simple explanation. This guide explains what ALT is, typical ranges for men and women, what mildly and markedly raised results can mean, the common causes, what UK guidance suggests next, and the symptoms that need urgent help. For the other liver markers, see our liver function test results guide.

Test it in Chiswick: our ALT blood test costs £59, with your result explained in person by a practitioner. No GP referral needed. Book this test or call 020 4515 0000. Prefer to test at home? A home finger-prick kit is also available, ask us when you enquire, or see our home kit options.

Better value: our Liver Health Check Plus costs £49 and measures ALT together with AST, ALP, GGT, bilirubin, albumin and ferritin, so for most people it is the better choice. Book the Liver Health Check Plus.

Quick answer

ALT is a liver enzyme. Many NHS laboratories use an upper limit of about 50 U/L for men and 35 U/L for women, but ranges vary, so check the range on your report. A mild to moderate rise, roughly 40 to 200 U/L, is common and is usually looked into on a routine basis. Fatty liver, alcohol and medicines are frequent causes. UK guidance says the size of the rise is not always a guide to how serious the cause is, so the aim is to find the reason. Yellow skin or eyes need urgent advice.

What is ALT?

ALT helps liver cells process protein. Most of it stays inside the cells, so only a small amount is normally found in the blood. When liver cells are damaged or inflamed, for example by fat build-up, alcohol, a virus or a medicine, ALT levels in the blood rise. Small amounts of ALT are also found in muscle, so a muscle injury or very hard exercise can push it up too.

ALT is reported in U/L or IU/L (units per litre). It is usually measured as part of a liver function test, alongside AST, ALP, GGT, bilirubin and albumin, because the pattern across these markers helps point to the cause.

Normal ALT levels for men and women

Each laboratory sets its own range, so always use the one on your report. As an example, one NHS laboratory uses:

• Men: below 50 U/L
• Women: below 35 U/L

Men tend to have slightly higher ALT than women, which is why many laboratories use separate limits. The British Society of Gastroenterology (BSG) notes that the current upper limit for some liver enzymes, including ALT, may be set too high. A result near the top of the range is not automatically reassuring if you have risk factors for liver disease.

Mildly and markedly raised ALT

• Within range: reassuring, but NICE advises that routine liver blood tests should not be used to rule out fatty liver, so a normal ALT does not exclude it if you have risk factors.
• Mild to moderate rise (roughly 40 to 200 U/L): NHS liver pathway guidance says this usually needs investigation on a routine basis. Fatty liver, alcohol and medicines are the most common reasons.
• Very high, or raised while you feel unwell: a high ALT with a feverish or flu-like illness can point to acute hepatitis. NHS guidance advises urgent assessment if you are unwell or have a fever.

The BSG guideline on abnormal liver blood tests makes an important point: the extent of the abnormality is not necessarily a guide to how significant it is. A modest rise that lasts can matter more than a short spike after a virus.

Common causes of a high ALT

Fatty liver (MASLD)

An NHS laboratory guide for GPs describes metabolic dysfunction-associated steatotic liver disease (MASLD), previously called non-alcoholic fatty liver disease, as the most common cause of abnormal liver tests in people without symptoms. The NHS says it is more likely if you carry weight around your waist, have type 2 diabetes, high blood pressure or high cholesterol, have polycystic ovary syndrome or are over 50. Many people have it without realising. Our guide to blood tests for fatty liver explains how it is checked.

Alcohol

Regular drinking above recommended limits can raise ALT and other liver enzymes. The NHS advises keeping to no more than 14 units a week. NHS pathway guidance suggests stopping alcohol and repeating liver tests after 1 to 3 months when alcohol is a likely cause.

Medicines, supplements and herbal remedies

Many medicines can affect liver enzymes. NHS laboratory guidance lists examples including statins, some antibiotics (such as macrolides, nitrofurantoin and minocycline), methotrexate, carbamazepine and terbinafine. Over-the-counter and herbal products can do the same. Do not stop a prescribed medicine without talking to your GP, as a small rise is often expected and safe.

Viral hepatitis

Long-term hepatitis B or C infection can cause a raised ALT for years without symptoms. A recent infection, such as hepatitis A or E or glandular fever, can cause a sharp rise with a flu-like illness. We offer a hepatitis B test and a hepatitis C test.

Muscle injury, hard exercise or a passing illness

NHS laboratory guidance notes that ALT, and AST even more so, can come from muscle, so a creatine kinase (CK) test may be added if there is no other cause. An isolated raised ALT can also be short-lived after a viral infection and settle within a few weeks.

Less common causes

These include autoimmune hepatitis and inherited conditions such as haemochromatosis (iron overload), Wilson disease and alpha-1 antitrypsin deficiency, which is why a family history of liver disease matters.

What usually happens after a high ALT

1. A review of likely causes. Alcohol, medicines, supplements and recent exercise are looked at first.
2. A recheck when there is an obvious cause. NHS pathway guidance suggests repeating liver tests 1 to 3 months after stopping alcohol or a suspected medicine.
3. A liver screen when there is no clear cause. The BSG recommends looking for the cause rather than simply repeating the same tests. A standard screen includes an abdominal ultrasound, hepatitis B and C tests and liver antibodies, often with iron studies.
4. Checking for scarring in fatty liver. The BSG recommends the FIB-4 score as a first test, with a low score being below 1.3 under 65, or below 2.0 over 65. NICE guideline NG49 also describes the enhanced liver fibrosis (ELF) test.
5. Specialist advice if it persists. NHS guidance notes that many specialists look further when ALT has stayed raised for more than 6 months.

When to get urgent help

• Ask for an urgent GP appointment or contact NHS 111 if your skin or the whites of your eyes look yellow (jaundice). You may also notice itchy skin, darker pee and paler poo.
• Get same-day medical advice if you have a raised ALT and feel unwell or have a fever.
• Call 999 or go to A&E if you vomit blood and feel unwell, confused, faint or dizzy, or have black poo.

Do not wait for a private blood test result in any of these situations.

Who should consider an ALT test?

• People with risk factors for fatty liver, such as extra weight around the waist, type 2 diabetes, high blood pressure or high cholesterol
• People who drink regularly or want to check their liver after cutting down
• People taking medicines that can affect the liver
• Anyone following up a previous raised ALT

Preparing for your test

You do not usually need to fast for an ALT test, but we will tell you if another test in your booking needs it. Avoid unusually hard exercise in the days before, as it can raise muscle enzymes. Tell us about alcohol, prescribed medicines, supplements and herbal remedies.

How often to retest

When a likely cause has been removed, a repeat after 1 to 3 months is typical. After lifestyle changes for fatty liver, NHS pathway guidance suggests rechecking liver tests after 9 to 12 months. Your GP will advise if further tests are needed.

Frequently asked questions

Is an ALT of 60 high?

It is above many laboratory limits for both men and women, but it is a mild rise. It is worth reviewing alcohol, medicines and recent exercise, and discussing a recheck and possible liver screen with your GP.

Is an ALT of 100 serious?

Not necessarily. It falls in the mild to moderate band, which NHS guidance usually investigates routinely. It should not be ignored, and it needs urgent attention if you also feel unwell or have jaundice.

Can exercise raise ALT?

Yes. ALT is also found in muscle, so very hard exercise or a muscle injury can raise it. AST is affected even more. A creatine kinase test can help show whether muscle is the source.

Can ALT go back to normal?

Often, yes. ALT usually settles once the cause is removed, for example after cutting down on alcohol, changing a medicine or losing weight with fatty liver.

What is the difference between ALT and AST?

Both are enzymes that rise when liver cells are irritated. ALT is more specific to the liver, while AST is also found in muscle. Clinicians read them together, and they are part of the FIB-4 score.

ALT testing in Chiswick

We take your blood sample at our clinic at 8 to 9 Bedford Corner, The Avenue, Chiswick, London W4 1LZ, a short walk from Turnham Green station on the District line (Piccadilly line trains stop there early morning and late evening only), and on the 94, E3 and 272 bus routes. Limited parking is available on request when you book. Your sample is analysed at the Randox accredited laboratory, most results are back within a few working days, and a practitioner talks you through what your result means. No GP referral is needed, and we can send a GP feedback report on request.

Book a single ALT blood test, or check ALT alongside six more markers with our Liver Health Check Plus. You can also compare every blood test and price, read our liver function test results guide, or learn about blood tests for fatty liver.

This article is general information, not medical advice. Discuss your results with your GP or practitioner.