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.
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:
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.
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.
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:
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.
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:
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 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.
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.
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.
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.
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:
The vast majority of referrals result in reassurance and a monitoring plan, rather than a diagnosis of serious liver disease.
Most abnormal liver function tests are not an emergency, but certain symptoms alongside abnormal results should prompt more urgent assessment. These include:
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.
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.
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.
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.
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 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.
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.
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.
A normal result means each marker, including ALT, AST, ALP, GGT, bilirubin and albumin, falls within the reference range shown on your laboratory report. These ranges can vary between laboratories, so your results should always be interpreted against the range provided on your own report.
Usually not on its own. A mildly raised ALT can be caused by fatty liver disease, recent alcohol intake, certain medications or strenuous exercise. Your doctor may recommend repeating the test after a few weeks before deciding whether further investigation is needed.
A raised GGT can be associated with regular alcohol intake, certain medications or problems affecting the bile ducts. GGT is interpreted alongside other liver markers rather than in isolation.
Yes. Alcohol can temporarily raise GGT and, with heavier intake, may also increase ALT and AST. This is why alcohol consumption is usually considered when interpreting abnormal liver function test results.
Yes. Intense or unfamiliar exercise can temporarily increase AST and, to a lesser extent, ALT because these enzymes are also found in muscle tissue. Levels usually settle within a few days.
Fasting is generally not required when testing liver enzymes alone. However, if your blood test also includes cholesterol or glucose, you may be asked to fast, depending on the tests being performed.
Yes. LFTs measure enzymes and proteins associated with the liver rather than directly measuring liver scarring. As a result, some people with liver disease can have normal blood test results, which is why further tests or imaging may sometimes be needed.
It depends on why the test was performed and what the results show. A mildly abnormal result may be repeated after around four to twelve weeks, while people taking medicines that can affect the liver or those with an existing liver condition may need more regular monitoring.
NAFLD and MASLD refer to the same underlying condition. The term NAFLD, or non-alcoholic fatty liver disease, was renamed metabolic dysfunction-associated steatotic liver disease (MASLD) in 2023 to better reflect its links with metabolic health.
You should arrange a medical assessment if a repeat test remains abnormal or if you develop symptoms such as jaundice, dark urine, persistent itching or unexplained weight loss. Confusion, vomiting blood or passing black, tarry stools require emergency medical attention.
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