Blood tests · Pillar guide
Understanding Liver Function Tests
Liver function tests (LFTs) are a group of blood results read together. This guide explains what each marker looks at, how they relate, and what may happen next — in plain English.
Medipher explains medical wording in plain English — it does not diagnose or replace a clinician. If this is a medical emergency, call your local emergency number immediately.
Part of the Blood Tests guides
This guide covers one panel in detail. If you are new to blood test reports, the general guide is a good place to start.
What are these tests?
Liver function tests — often shortened to LFTs — are a group of measurements taken from a single blood sample. Despite the name, they don't measure one thing called "liver function". They measure enzymes and proteins that are made by, processed by, or released from the liver and nearby bile ducts.
Because these substances move into the blood in predictable ways, a pattern across several results can tell a healthcare professional something useful about how the liver and bile system are working at that moment.
Having LFTs requested is very common. It is often part of a routine check, a medication review, or an investigation of general symptoms — not a sign that a liver problem has been found.
Diagram: Liver cells and bile ducts, then Enzymes released, then Blood test, then Pattern read together.
Liver tests mostly measure substances that leak into the blood, plus things the liver makes.
Where this test fits
- Check or symptomsWhy the test was ordered
- ALTLiver cell enzyme
- BilirubinFrom old red cells
- Pattern and repeatOften rechecked
Tests are rarely read on their own. Follow any step to learn about that part of the picture.
Why is it measured?
Being asked for these tests is common and does not, by itself, suggest that anything has been found. Healthcare professionals request them for many everyday reasons.
Common reasons these tests are requested
- As part of a routine or general health check
- Before starting, or while taking, medicines that are processed by the liver
- To look into symptoms such as tiredness, itching, nausea or abdominal discomfort
- When skin or the whites of the eyes look yellow (jaundice)
- To monitor a known liver or bile-duct condition over time
- Alongside other panels such as a full blood count or kidney function tests
What do the individual results mean?
Reference ranges vary between laboratories and between individuals, so always compare a value with the range printed on your own report.
Alanine aminotransferase
ALTAn enzyme found mostly inside liver cells.
- Why it is included
- When liver cells are irritated or damaged, ALT leaks into the blood, so it is used as a general marker of liver-cell irritation.
- If the result is higher
- A raised ALT can be associated with liver-cell irritation from many causes, including fatty change in the liver, alcohol, viral infections, and some medicines. Mild rises are common and often temporary.
- If the result is lower
- Low ALT is not usually considered clinically significant on its own.
Aspartate aminotransferase
ASTAn enzyme found in the liver, but also in muscle and other tissues.
- Why it is included
- AST is usually read alongside ALT. Because it is not specific to the liver, the relationship between the two is often more informative than AST alone.
- If the result is higher
- A raised AST may be seen with liver-cell irritation, but can also follow strenuous exercise or muscle injury, since muscle tissue releases AST too.
- If the result is lower
- Low AST is not usually considered clinically significant on its own.
Alkaline phosphatase
ALPAn enzyme linked to the bile ducts, and also to bone.
- Why it is included
- ALP helps distinguish problems with bile flow from problems inside the liver cells themselves. It is also naturally higher during growth and in pregnancy.
- If the result is higher
- A raised ALP can be associated with slowed bile flow, but also with bone turnover, pregnancy, and normal growth in children and teenagers. Interpretation depends heavily on the other results.
- If the result is lower
- Low ALP is uncommon and is usually reviewed alongside other results.
Bilirubin
BilirubinA yellow-orange substance made when red blood cells are broken down.
- Why it is included
- The liver processes bilirubin so it can leave the body. Measuring it shows how well that pathway is working.
- If the result is higher
- A raised bilirubin can be associated with slower processing or clearance of bilirubin, faster red-cell breakdown, or a harmless inherited variation called Gilbert's syndrome, which is common. Visible yellowing of the skin or eyes should always be discussed with a healthcare professional.
- If the result is lower
- Low bilirubin is not usually considered clinically significant.
Albumin
AlbuminThe main protein made by the liver and carried in the blood.
- Why it is included
- Albumin reflects longer-term liver protein production, nutrition and general health, rather than short-term irritation.
- If the result is higher
- A high albumin is uncommon and is often related to dehydration or how the sample was taken.
- If the result is lower
- A lower albumin may be seen in longer-standing illness, inflammation, poor absorption of nutrients, or some kidney conditions. It is always interpreted alongside other results.
Gamma-glutamyl transferase
GGTAn enzyme related to the bile ducts, not always included in every panel.
- Why it is included
- GGT is often added when ALP is raised, to help work out whether the rise is more likely to be coming from the liver and bile ducts or from bone.
- If the result is higher
- A raised GGT can be associated with bile-flow changes, alcohol intake and certain medicines. On its own it is not a diagnosis of anything.
- If the result is lower
- Low GGT is not usually considered clinically significant.
What this doesn't necessarily mean
- A mildly raised ALT does not automatically mean liver disease — recent exercise, alcohol, infection and some medicines can all cause temporary changes.
- A raised bilirubin does not automatically mean something serious — Gilbert's syndrome is a common, harmless inherited variation.
- Normal liver tests do not rule out every liver condition, which is why symptoms still matter.
Looking at your own liver results? Medipher can explain the terminology in plain English. Explain my result
Understanding your results: normal, high and low
Laboratories print their own reference range beside each result, and what counts as usual differs between people. Doctors read a value alongside your symptoms, medical history, medicines and other tests — so a number just outside the range is often not a problem on its own.
ALT
- Lower than the usual range
- A lower ALT is not generally treated as a finding.
- Within the usual range
- An ALT in the usual range suggests no significant leak from liver cells at the time of the test.
- Higher than the usual range
- A raised ALT can follow many everyday things — recent alcohol, some medicines and supplements, a viral illness, or fatty change in the liver. Mild rises are common and are usually rechecked.
Should I worry?
Liver results move for ordinary reasons and often settle on a repeat test. Clinicians look at the pattern across several values rather than at one raised enzyme.
Bilirubin
- Lower than the usual range
- A lower bilirubin is not usually significant.
- Within the usual range
- A bilirubin in range suggests the usual handling of old red blood cells is going as expected.
- Higher than the usual range
- A raised bilirubin can accompany a very common harmless inherited variation, as well as other causes. It is read with the enzyme pattern.
Albumin
- Lower than the usual range
- A lower albumin can follow acute illness, inflammation or nutrition, as well as liver-related changes, so it is never read alone.
- Within the usual range
- An albumin in range is one of the reassuring signs about the liver's ongoing production.
- Higher than the usual range
- A higher albumin is often related to hydration at the time of the test.
Questions you could ask your doctor
- Is the pattern across my liver results, rather than one value, what matters here?
- Could a medicine, supplement or recent illness explain this?
- Should the test be repeated, and when?
- Are any further tests needed?
Understanding the results together
Healthcare professionals rarely read a single liver result on its own. They look at the pattern — which markers are raised, by how much, and in what combination — and then interpret it alongside your symptoms, history and medicines.
A very small movement outside a reference range is common and often means little. A pattern that repeats over several tests, or a marker that is substantially higher than the rest, tends to carry more weight.
ALT and AST raised together, with normal ALP
This pattern points more towards the liver cells than the bile ducts. It has many possible explanations and would usually be interpreted alongside your history, medicines and other results.
ALP raised with a normal ALT
A clinician may consider whether the rise is coming from bile ducts or from bone, and may look at GGT or other tests to help distinguish them.
Isolated mildly raised bilirubin, everything else normal
This combination is frequently associated with Gilbert's syndrome, a harmless and common inherited variation — but only a healthcare professional can confirm what applies to you.
These are illustrations of how results are read together — they are not a way of working out a diagnosis from your own numbers.
What can affect the results?
An unexpected result usually has more than one possible explanation. Some of the more common influences include:
- Recent alcohol intake
- Some prescription medicines, over-the-counter painkillers and herbal or bodybuilding supplements
- Strenuous exercise shortly before the blood test (particularly AST)
- Recent viral illness or infection
- Pregnancy and normal growth in children and teenagers (particularly ALP)
- Body weight and metabolic health
- Inherited variations such as Gilbert's syndrome
- Differences between laboratories in how results are measured and reported
What happens next?
There is no single route after an unusual result. Depending on the whole picture, a healthcare professional may consider any of the following — none of them is guaranteed.
- Repeating the blood test after a period of time, to see whether the change persists
- Reviewing your other results together rather than one marker at a time
- Talking through your symptoms and medical history
- Reviewing medicines, supplements and alcohol intake
- Requesting additional blood tests to look for specific causes
- Arranging an ultrasound or other imaging of the liver area
- Simply monitoring the results over months rather than acting immediately
Questions you could ask
These are prompts to help you have a more informed conversation — not a way to interpret results yourself.
- Which of my liver results were outside the reference range, and by how much?
- Could any of my medicines or supplements be affecting these results?
- Will this test need to be repeated, and when?
- Are my other blood results relevant to this one?
- Is there anything I should monitor or notice between now and my next test?
- Is any further investigation being considered?
Frequently asked questions
Do liver function tests measure how well my liver works?
Not exactly. They measure enzymes and proteins related to the liver and bile ducts. They give a useful snapshot, but they are not a direct measurement of overall liver function, and they are always interpreted alongside other information.
Should I fast before liver function tests?
It depends on which tests are requested at the same time. Your healthcare professional or the blood test appointment letter will tell you if fasting is needed.
Why is my result flagged when it is only slightly outside the range?
Laboratory systems flag anything outside the reference range automatically. Reference ranges describe most healthy adults, so results can sit slightly outside them without indicating a problem.
Can alcohol affect these results?
Alcohol can influence several liver-related markers. If your results are being reviewed, it is worth being open about your usual intake so they can be interpreted accurately.
Related medical terms
Each term has its own plain-English page in the Medipher medical glossary.
- ALTAn enzyme found mainly in liver cells. It leaks into the blood when the liver is irritated or damaged.
- ASTAn enzyme found in the liver, muscle and other tissues. It rises when these tissues are irritated or damaged.
- BilirubinA yellow substance made when old red blood cells are broken down. The liver processes it and removes it in bile.
- AlbuminThe main protein in your blood, made by the liver. It helps keep fluid inside your blood vessels.
Commonly confused with
These tests sound similar to Liver Function Tests, but each answers a different question.
- Hepatitis blood testsThose look for specific viruses, whereas liver function tests describe how the liver is behaving generally.
- Liver ultrasoundA scan looks at the structure of the liver; blood tests look at its chemistry.
- GGTGGT is an extra enzyme sometimes added to the panel to help interpret a raised ALP.
Learning collections
Work through this topic step by step, from the basics to the questions worth asking your doctor.
Sources
Medipher uses publicly available information and guidance from trusted health organisations in the UK and internationally, where relevant. They are educational and do not replace advice from your own healthcare professional.
- 01MedlinePlus (US National Library of Medicine) — United StatesLiver Function Tests
- 02Healthdirect Australia — AustraliaLiver function tests (LFTs)
- 03NHSGeneral backgroundBlood tests — Health A to Z
- 04Association for Laboratory MedicineGeneral backgroundLab Tests Online UK — Tests index
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About this page
- Author
- Omer Suliman
- Medical reviewer
- Clinical review pending
- Last reviewed
- 12 August 2026
- Last updated
- 12 August 2026
Evidence. Written from public patient-information sources including the NHS, NICE and the Association for Laboratory Medicine, and reviewed for plain-English accuracy before publication.
Educational content only. Medipher explains medical language in plain English. It does not diagnose, and it is not a substitute for advice from a doctor, nurse or pharmacist. Read the medical disclaimer.
Responsible AI. Where Medipher uses AI to explain a document, the output is a plain-English translation of what you provided — never a diagnosis. How we use AI.
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Medipher can help explain the medical language in plain English, highlight the terms used and suggest questions to take to your healthcare professional. It does not provide a diagnosis or medical advice.
This guide is general health information, not medical advice, and it cannot diagnose any condition. Reference ranges and clinical interpretation vary between laboratories and individuals — always discuss your own results with a GP, doctor, nurse or pharmacist.