Liver Function Tests Explained: What Your Results Mean

Written by Dr. Simon Khela MBChB MRCGP, GMC Registered Doctor

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Liver function tests, usually shortened to LFTs, are among the most frequently requested blood tests in UK general practice. They are ordered as part of routine health checks, before starting certain medications, during pregnancy, and when investigating symptoms such as fatigue, nausea or abdominal discomfort. Despite how often they are requested, many patients are simply handed a printed results sheet with a row of unfamiliar abbreviations and little explanation of what any of it actually means.

One of the most common questions I am asked in clinic is what it means when a patient’s ALT or GGT comes back “slightly raised” on an otherwise unremarkable blood test. In most cases the answer is reassuring, but understanding the reasoning behind that reassurance helps patients feel more in control of their own health rather than anxiously googling a number on a page.

This article explains what liver function tests actually measure, what the different patterns of results can suggest, the most common causes of an abnormal result in the UK population, and when a result genuinely needs prompt medical attention rather than simple monitoring.

What Is a Liver Function Test?

A liver function test is a blood test that measures a group of enzymes, proteins and waste products that are made or processed by the liver, most commonly ALT, AST, ALP, GGT, bilirubin and albumin. Despite the name, LFTs do not directly measure how well the liver is “functioning”; they mainly flag possible liver cell damage, a problem with bile flow, or reduced production of certain proteins.

Liver function tests are typically requested:

• As part of routine health screening, workplace medicals or a general health check.
• Before starting medications known to affect the liver, such as statins or certain antibiotics.
• When investigating unexplained fatigue, nausea, itching or abdominal discomfort.
• To monitor a known liver condition, or ongoing alcohol-related risk.
• As part of a wider private blood test panel alongside cholesterol, glucose or thyroid checks.

What Do Liver Function Tests Actually Measure?

A standard liver panel usually includes several separate measurements, each telling doctors something slightly different about the liver, as the British Liver Trust explains in more detail. Reference ranges vary between laboratories, sex and age, so always interpret your results against the range printed on your own report rather than a generic figure found online.

*Ranges are approximate and vary between laboratories. Your own report will state the reference range used by the testing laboratory.

Understanding the Pattern, Not Just One Number

Many patients are surprised to learn that GPs rarely interpret a single liver enzyme in isolation. A raised ALT on its own means something quite different from a raised ALT alongside a raised ALP, or a raised bilirubin with otherwise normal enzymes. Looking at the overall pattern is usually more informative than focusing on any one number.

Common Causes of Abnormal Liver Function Tests

In UK general practice, most abnormal liver function tests are mild and reflect a manageable underlying cause rather than serious liver disease. The most frequent causes I see in clinic include:

• Fatty liver disease (MASLD). Now known as metabolic dysfunction-associated steatotic liver disease, previously called NAFLD, this is linked to excess weight, type 2 diabetes and symptoms of high cholesterol, and is the most common cause of a mildly abnormal liver test in the UK.
• Alcohol. Regular drinking, even close to the recommended UK limit of 14 units a week, can raise GGT. Heavier or binge drinking tends to raise ALT and AST as well.
• Medications and supplements. Statins, some antibiotics, anti-epileptic drugs and certain herbal or over-the-counter supplements can all affect liver enzymes.
• Viral hepatitis. Hepatitis A, B and C can all cause abnormal liver tests, sometimes without any obvious symptoms.
• Gallstones or bile duct obstruction. These typically produce a cholestatic pattern, with ALP and GGT rising more than ALT and AST.
• Autoimmune liver disease. Less common, but should be considered when other causes have been excluded.
• Inherited conditions. Gilbert’s syndrome, haemochromatosis and, more rarely, Wilson’s disease can all affect liver blood tests.
• Recent illness or exercise. A minor infection or a heavy gym session in the days before a blood test can cause a transient, harmless rise in liver enzymes.

A patient I saw recently was understandably alarmed after a routine work medical flagged a mildly raised ALT. He had run a half marathon two days before the test and had no other symptoms. A repeat test four weeks later, taken well away from any exercise, was entirely normal. This kind of transient elevation is far more common than most patients realise, which is exactly why a single abnormal result rarely leads straight to a diagnosis.

What Does a Mildly Raised Result Usually Mean?

Mild to moderate elevations, roughly up to two or three times the upper limit of normal, are common and, as Patient.info notes in its guidance for patients, often reflect fatty liver or lifestyle-related factors rather than serious disease. These results frequently improve with weight loss, reduced alcohol intake or simply stopping a contributing medication, and often resolve without any specific treatment.

When a GP sees a mildly abnormal result, they will usually:

• Review alcohol intake, current medications and any recent illness.
• Arrange a repeat test after a few weeks to see whether the result has changed.
• Consider additional tests, such as fasting glucose or HbA1c, cholesterol, a hepatitis B and C screen, or ferritin.
• Arrange a liver ultrasound scan if fatty liver disease is suspected.
• Calculate a fibrosis risk score, such as FIB-4, if fatty liver is confirmed on scanning.

Fibrosis Risk Scoring: What Is FIB-4?

When fatty liver disease is confirmed, doctors increasingly use a simple calculation called FIB-4, which combines age, ALT, AST and platelet count, to estimate the likelihood of more advanced liver scarring, known as fibrosis. A low FIB-4 score is reassuring and generally means ongoing monitoring in primary care is appropriate. A higher score prompts a referral to a liver specialist for further assessment, which may include a Fibroscan, a non-invasive test that measures liver stiffness.

Liver Function Tests in Special Situations

Liver function tests are also used routinely in a few specific situations beyond general health screening, and the reasons for testing, and what an abnormal result might mean, can differ slightly in each case.

During Pregnancy

LFTs may be checked if a pregnant woman develops persistent itching, particularly on the palms and soles, without a rash. This can be a sign of obstetric cholestasis, a pregnancy-specific liver condition that causes raised bile acids and sometimes raised ALT, and which needs prompt midwifery and obstetric review because of the small associated risk to the baby.

Before and During Certain Medications

Doctors often check liver function before starting, and periodically during treatment with, medications that are processed by the liver or can occasionally cause liver inflammation. Common examples include statins for cholesterol, methotrexate for autoimmune conditions, isotretinoin for severe acne, and some long-term pain relief or epilepsy medications. Routine monitoring in these situations is a precaution, not a sign that something has already gone wrong.

Inherited and Less Common Causes

Occasionally, abnormal liver function tests lead to testing for inherited conditions. Haemochromatosis causes the body to absorb too much iron, which can build up in the liver over years, and is checked for using ferritin and transferrin saturation blood tests. Wilson’s disease, a rare inherited disorder of copper metabolism, is usually only considered in younger patients with unexplained liver abnormalities, and is investigated with a caeruloplasmin blood test. Both conditions are uncommon but treatable when caught early, which is part of the reason doctors sometimes request further tests after ruling out the more common causes.

What Happens If You’re Referred to a Liver Specialist?

Most people with mildly abnormal liver function tests never need to see a specialist, since the cause is usually identified and managed in general practice. A referral is more likely if results remain significantly abnormal despite lifestyle changes, if a fibrosis risk score is high, or if a specific condition needs specialist confirmation. A first hepatology or gastroenterology appointment typically involves:

• A detailed review of alcohol intake, medications, family history and risk factors.
• Further blood tests, which may include autoimmune liver screens, iron studies, or a caeruloplasmin level depending on the suspected cause.
• A Fibroscan, a quick, painless scan that measures liver stiffness as an indicator of scarring.
• In a minority of cases, a liver biopsy, if non-invasive tests cannot give a clear enough answer.

The vast majority of referrals result in reassurance and a monitoring plan, rather than a diagnosis of serious liver disease.

When Should You Be More Concerned?

Most abnormal liver function tests are not an emergency, but certain symptoms alongside abnormal results should prompt more urgent assessment. These include:

• Yellowing of the skin or the whites of the eyes (jaundice).
• Dark urine or unusually pale, chalky stools.
• Persistent itching without an obvious rash.
• Unexplained weight loss.
• Swelling of the abdomen or legs.
• Confusion or unusual drowsiness.
• Vomiting blood, or passing black, tar-like stools.

If you notice jaundice, dark urine or persistent itching, arrange a prompt GP assessment. If you experience confusion, vomit blood, or pass black, tarry stools, this is a medical emergency: call 999 or go to your nearest A&E immediately rather than waiting for a routine appointment.

Fatty Liver Disease and Alcohol-Related Liver Disease Compared

These two conditions are the most common causes of abnormal liver function tests in the UK and are sometimes confused with one another, though the underlying drivers and management are different.

Common Myths and Misconceptions

“Normal liver function tests mean my liver is definitely healthy.”

Not necessarily. Liver function tests measure enzyme leakage and protein production, not scarring itself, so results can remain normal even in fairly advanced liver disease. This is one reason doctors sometimes recommend imaging or additional tests even when LFTs look reassuring.

“A raised liver test means I have liver disease.”

Also not necessarily. Many transient factors, including recent exercise, a minor viral illness, or a particular medication, can temporarily raise liver enzymes. A repeat test after a few weeks is usually the sensible first step before drawing any conclusions.

“Only heavy drinkers get abnormal liver tests.”

Fatty liver disease linked to weight and metabolic health, rather than alcohol, is now the most common cause of an abnormal liver function test seen in UK general practice.

“Fatty liver isn’t serious because it isn’t caused by alcohol.”

Fatty liver disease is usually mild and manageable through lifestyle change, but in a minority of people it can progress to inflammation and scarring if left unaddressed, which is why monitoring matters.

“I need to fast before a liver blood test.”

Fasting generally isn’t required for liver enzymes alone, although it may be requested if cholesterol or glucose are being tested from the same sample.

“If I stop drinking, my results will improve immediately.”

Cutting down or stopping alcohol is one of the most effective things you can do for your liver, but enzyme levels do not always normalise straight away. GGT in particular has a longer half-life and can remain raised for several weeks after intake stops, so doctors usually wait before repeating a test to get an accurate picture.

How to Prepare for a Liver Function Test

• Avoid heavy alcohol intake for 24–48 hours beforehand where possible, as this can temporarily affect results.
• Tell your doctor about all regular medications, supplements and herbal remedies, since several can affect liver enzymes.
• Fasting usually isn’t required for liver enzymes alone, but follow any specific instructions given if other tests are being taken at the same time.
• Wear a top with sleeves that can be easily rolled up for the blood draw.
• If you are unsure what your results mean once they arrive, book an online GP consultation to discuss them with a doctor.

Protecting Your Liver Health

• Keep alcohol intake within UK guidelines of no more than 14 units a week, spread across three or more days, as covered above.
• Aim for a gradual, sustainable weight loss if you carry excess weight, which can meaningfully improve fatty liver over time; ask about weight management support if you would find this helpful.
• Review long-term medications and supplements periodically with your GP, particularly regular paracetamol use or unregulated herbal products.
• Consider hepatitis A and B vaccination before travelling to higher-risk regions; this can usually be arranged alongside routine travel vaccinations.
• If there is any risk of exposure to hepatitis B or C, arrange sexual health screening to check your status.
• Attend any follow-up blood tests your doctor has recommended, even if you feel completely well.

Frequently Asked Questions about Liver Health