Liver Function Test: What Each Result Means and Common Causes 

Opening a blood test report filled with acronyms like ALT, AST, and ALP, alongside numbers flagged in red as 'high' or 'low', can understandably cause anxiety. In our virtual consultations, patients frequently bring us their results feeling confused and worried about what these markers mean for their health.

Liver function tests are a very common and useful panel of blood tests that provide a snapshot of your liver health. For a patient in the UK, understanding these results is the helpful first step in a conversation with your GP, rather than a definitive diagnosis on its own.

This article is for general information and does not replace advice from a qualified clinician. It is written for anyone who has been advised to have a liver function test, has recently received their results, or is simply curious about monitoring their liver health. It demystifies the numbers, explains common causes for abnormal results, and outlines what happens next.

What is a liver function test?

A liver function test is a routine panel of blood tests used to help diagnose and monitor liver disease or damage by measuring the levels of specific enzymes and proteins. Because your liver produces these substances, changes in their levels can indicate how well the organ is working or if its cells are inflamed.

According to the NHS, a standard UK liver panel typically includes ALT, AST, ALP, GGT, bilirubin, and albumin.

Why doctors order this test

There are four main reasons a doctor may recommend a liver function test:

• Screening: To check for underlying liver problems, particularly in people who might be at a higher risk due to a family history of liver disease, being overweight, or heavy alcohol use.
• Diagnosis: To investigate specific symptoms you may be experiencing, such as jaundice (yellowing of the skin or eyes), unexplained abdominal pain, dark urine, or persistent fatigue.
• Monitoring: To track the progress of a known liver condition, such as hepatitis or fatty liver disease, and to see if a treatment is working.
• Medication safety: To check if a newly prescribed medicine is affecting the liver, as many common drugs are processed by liver enzymes.

If you have new symptoms like jaundice, changes in urine and stool colour - will usually need an urgent assessment in hospital.

How to read your liver function test report

Reading a liver function test report involves looking at the specific markers tested, your numerical result, the laboratory's reference range, and the units of measurement.

Understanding report columns

When you view your blood test results, either on paper or via your NHS app, you will typically see four main columns:

• Test Name: The specific biochemical marker being measured (for example, Alanine Aminotransferase).
• Result: Your specific number detected in the blood sample.
• Reference Range: The normal expected range for the general healthy population, established by that specific laboratory.
• Units: The unit of measurement used, often U/L (units per litre) or g/L (grams per litre).

Example test report

To help make sense of your lab report, here is an illustration of how a typical test result is laid out and what each section means.

In this visual example, the ALT result of 65 U/L sits slightly above the expected reference range of 10 to 40 U/L, so the laboratory has flagged it as 'High'. The GP will use this context alongside the normal ALP and bilirubin to decide the next steps.

Reference ranges explained

It is important to know that "normal" ranges can differ slightly between different NHS and private laboratories based on the equipment they use. Factors like your age and sex can also influence your personal reference range. A result that falls slightly outside the laboratory's range is common and does not automatically mean you have a serious disease. Your GP will interpret the number in the context of your overall health and if concerned they can arrange more tests

Understanding each marker on your liver test

Each marker on your liver function test measures a different enzyme or protein, providing clues about liver inflammation, bile flow, or overall liver synthetic function.

ALT (Alanine aminotransferase)

Alanine aminotransferase (ALT) is an enzyme found mostly within the liver. Because it is highly concentrated in liver cells, it acts as a very sensitive marker of liver injury. As the British Liver Trust outlines, when liver cells become inflamed or damaged, they leak ALT into the bloodstream, causing elevated levels. High ALT is commonly seen in fatty liver disease, alcohol-related liver disease, viral hepatitis, and occasionally as a reaction to medications.

AST (Aspartate aminotransferase)

Aspartate aminotransferase (AST) is another enzyme found in the liver, but unlike ALT, it is also present in your muscles, heart, and red blood cells. High levels of AST can suggest liver cell damage similar to ALT. However, doctors often look at the ratio between AST and ALT to gather extra clues. For instance, an AST level that is significantly higher than the ALT level can point towards alcohol-related liver disease.

ALP (Alkaline phosphatase)

Alkaline phosphatase (ALP) is an enzyme heavily concentrated in the cells lining the bile ducts within the liver, though it is also found in bone and the gut. High levels of ALP usually suggest a problem with bile flow, known clinically as cholestasis. This can be caused by blockages like gallstones. Because ALP is also found in bones, a raised result can sometimes reflect a bone condition rather than a liver problem.

GGT (Gamma-glutamyl transferase)

Gamma-glutamyl transferase (GGT) is another enzyme found in the liver and bile ducts. It is often checked alongside ALP. If both ALP and GGT are raised, it suggests the issue lies in the bile ducts. According to BNF guidance, GGT is also extremely sensitive to alcohol consumption and can be elevated in fatty liver disease, making it a useful diagnostic tool.

Bilirubin

Bilirubin is a yellow waste product produced when old red blood cells are broken down. A healthy liver extracts bilirubin from the blood and excretes it into the bile. If bilirubin levels are high, it means the liver is not clearing it effectively. This build-up causes jaundice. Raised bilirubin is seen in liver disease and bile duct blockages, but it can also be raised in a common, harmless genetic variation called Gilbert's syndrome.

Albumin and total protein

Albumin is the main protein manufactured by the liver and circulates in your blood. Measuring albumin is a good test of liver function — its ability to synthesise vital materials. Low levels of albumin can indicate severe or chronic liver disease, such as cirrhosis, as the damaged liver can no longer produce enough protein. Albumin can also drop due to severe kidney disease or poor nutrition.

PT and INR (Clotting factors)

Prothrombin time measures how long it takes your blood to clot. The liver produces the vital proteins (clotting factors) required for this process. This test is not always included in a routine screening panel but is a crucial measure of liver function. As noted in BNF general prescribing guidance, a prolonged clotting time (a high INR result) suggests the liver is failing to make enough clotting factors, which can be an indicator of significant liver impairment.

What do patterns in your results mean?

Doctors interpret liver test results by looking for specific patterns across multiple markers, rather than focusing on a single abnormal number.

In clinical practice, we group the results into patterns because they provide a much clearer picture of what type of disease process is occurring. The table below outlines the most common clinical patterns and their meanings.

10 common causes of abnormal liver test results

The most common causes of abnormal liver function tests in the UK include fatty liver disease, alcohol use, certain medications, and temporary viral infections.

Many of the most frequent causes are directly related to lifestyle factors, meaning they are highly manageable and often reversible with the right guidance.

NAFLD (Fatty liver disease)

NAFLD is a build-up of excess fat in the liver cells. It is closely linked to carrying excess weight and having type 2 diabetes. The medical community increasingly refers to this condition as metabolic dysfunction-associated steatotic liver disease (MASLD). NICE guidelines highlight this as one of the leading causes of abnormal liver tests in the UK. You can read more in our non-alcoholic fatty liver disease guide.

ARLD (Alcohol-related liver disease)

Regularly drinking excessive amounts of alcohol over time causes progressive damage to liver cells, triggering inflammation and fat build-up. This commonly raises ALT, AST, and GGT levels. More information is available in our alcohol-related liver disease resource. If you think you are drinking too much or the people around you have concerned - it is important to get medical help. We can support you reducing alcohol safely.

Medications and supplements

The liver filters almost everything we ingest. Some medications can cause temporary liver inflammation. Common culprits include paracetamol (especially in overdose), certain antibiotics, anti-inflammatory medicines, statins, and a wide variety of over-the-counter herbal supplements. If you take regular medication don’t stop without speaking to your doctor.

Viral hepatitis

Viral hepatitis refers to specific viral infections that target and inflame the liver. Hepatitis A, B, and C can all cause significant spikes in liver enzymes, particularly ALT and AST. Learn more in our detailed viral hepatitis guide.

Gallstones or bile duct problems

Gallstones are hard, pebble-like deposits that form in the gallbladder. If a stone travels and blocks the main bile duct, bile backs up into the liver. This commonly triggers a cholestatic pattern on a liver test, raising ALP and GGT, and sometimes causing jaundice.

Autoimmune liver diseases

In autoimmune conditions, the body's immune system mistakenly attacks its own healthy tissue. Autoimmune hepatitis attacks the liver cells, while primary biliary cholangitis (PBC) attacks the small bile ducts within the liver. Both cause specific patterns of abnormal blood tests.

Genetic conditions

Certain inherited genetic disorders cause substances to accumulate in the liver, leading to damage over time. Examples include haemochromatosis, which causes dangerous iron overload, and Wilson's disease, which causes copper to build up in the liver and brain.

Temporary infections and exercise

You do not need a specific liver disease to have an abnormal liver test. Systemic viral infections like glandular fever can temporarily inflame the liver. Surprisingly, intense muscular exertion, like heavy weightlifting or a marathon, can also cause a short-term spike in AST levels.

Non-liver causes

Because some liver enzymes are found elsewhere in the body, raised results can occasionally point away from the liver entirely. A raised ALP in isolation might be investigated as a bone disease or vitamin D deficiency, whilst an isolated raised AST might stem from a recent muscle injury.

Follow-up for abnormal results

After an abnormal liver test result, your doctor will review your medical history, likely repeat the blood test, and arrange further investigations if the results remain elevated.

Step 1: Initial GP consultation

The first step is a consultation to discuss the result. A doctor will rarely make a definitive diagnosis based on one single, slightly abnormal test. They will ask you about any symptoms you are experiencing, your daily alcohol intake, your current medications (including supplements), and your family medical history to build a complete picture.

Step 2: Repeating the blood test

Because liver enzymes can fluctuate daily, it is common to wait and repeat the blood test after a few weeks or months. This helps the GP determine if the abnormal result was a temporary blip caused by a passing infection, or if the elevation is persistent and requires further attention. Whether they need urgent actions will be assessed by your doctor and will depend on how out of range they are.

Step 3: Further investigations

If your repeat blood test remains abnormal, your GP will recommend further investigations to identify the exact cause:

• Further blood tests: A more detailed panel (often called a 'liver screen') to check for viral hepatitis, autoimmune markers, and iron levels.
• Ultrasound scan: A painless scan to look at the physical structure of your liver and gallbladder, checking for fat accumulation or gallstones.
• FibroScan: A specialised ultrasound that measures liver stiffness to assess if there is any scarring (fibrosis).

Step 4: Referral to a hepatologist

If the cause of your abnormal results is complex, or if tests indicate advanced liver disease or scarring, your GP will refer you to a hepatologist. A specialist can offer a more in-depth assessment, confirm complex diagnoses, and initiate specialised treatments to protect your liver function.

Conclusion

Receiving an abnormal liver function test result is common. It is vital to remember that an LFT is a starting point for investigation, not a final diagnosis. The clinical pattern of your results provides far more insight than any single number being slightly out of the normal range. Furthermore, many of the most frequent causes, such as fatty liver disease, alcohol use, and medication effects, are highly manageable or entirely reversible.

The most important step you can take is to discuss your results with a healthcare professional who can put the numbers into the context of your overall health. If you have questions about your liver health or want to discuss a recent blood test report, book an appointment with a Doctor Care Anywhere GP for a private, consultation to guide your next steps.