What is ALT in a Blood Test?

If you've recently had a blood test and noticed something called ALT listed in your results, you might be wondering what it means. ALT stands for alanine aminotransferase - an enzyme that plays a key role in how your body processes protein. But why is it important, and what can it tell you about your health?

Measuring your ALT levels can give valuable insight into how your liver is functioning, and help spot signs of inflammation or damage before symptoms appear.

ALT in a blood test: what does it mean?

ALT is an enzyme that's mostly found in your liver cells, although smaller amounts are also present in your kidneys, heart and muscles. Under normal conditions, ALT levels in your bloodstream are low. But when your liver is injured or inflamed, ALT can leak into the bloodstream, which is why high levels are often used as a sign of liver stress or damage.

Testing your ALT levels is a common part of a liver function test, and it can help doctors assess the overall health of your liver and detect early changes that might need further investigation.

Why is ALT important?

Your liver is essential to many processes in your body, including:

• Breaking down toxins
• Metabolising nutrients
• Supporting your immune system
• Regulating blood sugar and cholesterol levels

Because of these critical functions, it's important to monitor your liver health and ALT is one of the key markers used to do that. Elevated ALT levels can be an early warning sign, even if you're not experiencing any noticeable symptoms.

What causes ALT levels to rise?

There are a range of factors that can cause ALT levels to rise. In many cases, this may be temporary and not a cause for concern, but persistent elevation should be taken seriously.

Common causes include:

• Liver inflammation (hepatitis) - due to viruses, alcohol or autoimmune conditions

• Fatty liver disease - often linked to obesity, insulin resistance or type 2 diabetes

• Alcohol misuse - long-term heavy drinking can damage liver cells

• Certain medications - including statins, antibiotics or paracetamol in high doses

• Viral infections - like mononucleosis or hepatitis B and C

• Muscle injury or intense exercise - can also sometimes raise ALT levels temporarily

• Toxin exposure - such as workplace chemicals or herbal supplements

Mildly raised ALT can be completely harmless in some people, while in others it might indicate something that needs monitoring or treatment.

What is a normal ALT range?

ALT is measured in units per litre of blood (U/L). Although ranges can vary slightly depending on the lab, a general guideline is:

• Men: 10-40 U/L

• Women: 7-35 U/L

It's worth noting that what's considered a "normal" level can depend on age, sex, body size and medical history. This is why ALT is usually assessed alongside other liver enzymes, such as AST (aspartate aminotransferase), ALP (alkaline phosphatase) and GGT (gamma-glutamyl transferase), to give a fuller picture of your liver health.

What if your ALT is high?

If your ALT result is higher than normal, it doesn’t automatically mean there’s a serious problem, but it does warrant a closer look.

Depending on your full test results, medical history and symptoms (if any), your healthcare provider might:

• Suggest repeating the test to see if levels remain elevated

• Recommend further liver function tests or imaging (like an ultrasound)

• Ask about lifestyle factors like alcohol, diet, medications or supplements

• Refer you to a specialist for further assessment

In many cases, lifestyle changes alone can bring ALT levels back to normal, especially if the cause is related to diet, alcohol intake or metabolic health.

Can ALT levels be too low?

It’s far more common to worry about elevated ALT than low levels. In most cases, low ALT isn’t considered clinically significant. However, abnormally low levels might sometimes be associated with:

• Vitamin B6 deficiency

• Chronic kidney disease

• Poor liver function in advanced disease

If ALT is low but all other liver markers are normal, it’s rarely cause for concern.

How to support healthy ALT levels

Taking care of your liver can help keep ALT levels within a healthy range. Even small lifestyle changes can have a big impact on keeping your liver healthy over time:

Limit alcohol intake Alcohol is one of the most common causes of raised ALT. Cutting back, or cutting it out, can reduce liver stress.

Maintain a healthy weight Fatty liver disease is closely linked to obesity and insulin resistance. Even modest weight loss can help lower ALT.

Eat a balanced, liver-friendly diet Focus on whole foods, plenty of vegetables, healthy fats and lean proteins. Limit highly processed foods and added sugars.

Exercise regularly Physical activity helps improve insulin sensitivity and supports liver function.

Be mindful of medications and supplements Some over-the-counter and herbal products can affect your liver. Always check with a healthcare provider before starting new ones.

Should you test your ALT levels?

ALT is typically measured as part of a routine health check or if there’s a specific reason to assess liver function. You might consider an ALT test if you:

• Are experiencing unexplained fatigue, nausea, or abdominal discomfort

• Have a history of alcohol use, hepatitis, or liver disease

• Take medications that affect the liver

• Are managing conditions like high cholesterol, obesity or type 2 diabetes

• Want to monitor your general health as part of a wellness check

ALT testing can help spot issues early, even before symptoms appear.

The Bluecrest approach to liver health

At Bluecrest Wellness, our private liver function test, measures key markers like ALT, an important enzyme that can indicate liver inflammation or damage. This test also includes other essential markers such as AST, ALP, GGT, and bilirubin, giving you a clear picture of your liver’s overall health.

You can book a private liver function blood test at a time and location that suits you, with 350+ clinics available across the UK. We partner with leading UK laboratories to deliver fast, reliable results and we’re fully accredited for a wide range of private health checks.

If you’re looking for a more complete overview, our complete Health MOT also includes ALT testing as part of an in-depth blood panel, designed to assess multiple aspects of your health in one convenient appointment.

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0800 652 2183 to speak to one of our team.