What Does a Liver Function Test Detect? Results Explained

Introduction

Your liver is one of the hardest-working organs in your body, performing over 500 essential functions including filtering toxins, producing bile, storing energy and processing nutrients. Despite its remarkable capacity to function under strain, liver problems often develop silently — producing few noticeable symptoms until significant changes have occurred. This is precisely why a liver function test is such a valuable component of preventive health screening.

A liver function test is a blood test that measures a group of enzymes, proteins and waste products to assess how well your liver is working. These markers — including ALT, AST, ALP, GGT, bilirubin and albumin — provide an objective snapshot of liver health and can highlight areas that may warrant further attention. Whether you are monitoring the effects of lifestyle factors, medication use, or simply taking a proactive approach to your wellbeing, liver function testing provides clarity that symptoms alone cannot. You can explore the full range of blood tests available at Private Blood Tests London to find the right panel for your needs.

A liver function test detects changes in liver enzymes, proteins and bilirubin levels in your blood. These markers help assess how well the liver is processing waste, producing proteins and managing bile flow. Abnormal levels may be associated with liver stress and may indicate a need for medical advice.

What Does a Liver Function Test Detect?

A liver function test detects changes in the levels of specific enzymes, proteins and metabolic byproducts that are produced or processed by the liver. When the liver is under stress — whether from lifestyle factors, medication effects, infection or other influences — these markers can shift outside their typical reference ranges, providing an early indication that something may need attention.

The key categories of markers assessed in a liver function test include:

Liver enzymes (ALT, AST, ALP, GGT) — These enzymes are found in liver cells and bile ducts. When liver cells are damaged or inflamed, they release higher levels of these enzymes into the bloodstream. Elevated liver enzyme levels are one of the earliest indicators of liver stress

Bilirubin — A yellow pigment produced when red blood cells break down. The liver processes bilirubin so it can be excreted from the body. Elevated bilirubin may suggest the liver is not processing waste efficiently. For a detailed exploration of this marker, our guide on what a bilirubin test measures provides further information

Proteins (albumin, total protein) — The liver produces several important proteins, including albumin. Low protein levels may suggest the liver's synthetic function is reduced

Metabolic indicators — The combined pattern of enzyme and protein levels helps build a picture of overall liver function, including how well the liver is managing its detoxification, protein synthesis and bile production roles

It is important to understand that a single abnormal marker does not constitute a diagnosis. Liver function test results are most informative when considered as a panel — the relationship between the different markers provides more meaningful insight than any individual value in isolation.

Key Markers in a Liver Function Blood Test

The following table summarises the key markers included in a standard liver function blood test. For access to a comprehensive liver panel, the liver function tests panel at Private Blood Tests London covers all of these markers in a single appointment.

Marker	What It Measures	General UK Reference Range	What High May Suggest	What Low May Suggest
ALT (Alanine Aminotransferase)	Liver cell health	7 – 56 U/L	May be associated with liver cell inflammation or damage	Generally not clinically significant when low
AST (Aspartate Aminotransferase)	Liver and muscle cell health	10 – 40 U/L	May be associated with liver or muscle cell damage	Generally not clinically significant when low
ALP (Alkaline Phosphatase)	Bile duct and bone health	44 – 147 U/L	May be associated with bile duct obstruction or bone conditions	May be associated with nutritional deficiencies in rare cases
GGT (Gamma-Glutamyl Transferase)	Bile duct function and alcohol-related liver stress	9 – 48 U/L	May be associated with alcohol use, bile duct issues or medication effects	Generally not clinically significant when low
Bilirubin	Red blood cell waste processing	3 – 17 µmol/L	May be associated with liver processing issues, bile duct obstruction or increased red cell breakdown	Generally not clinically significant when low
Albumin	Liver protein production	35 – 50 g/L	May be associated with dehydration in some cases	May be associated with reduced liver synthetic function or nutritional factors
Total Protein	Combined protein levels in blood	60 – 83 g/L	May be associated with chronic inflammation or infection	May be associated with liver or kidney concerns

These reference ranges are provided for educational purposes and may vary slightly between laboratories. Your blood test report will display the specific ranges used by the laboratory that processed your sample.

Understanding Liver Function Test Results

Interpreting liver function test results requires considering the overall pattern of markers rather than focusing on a single value. Understanding what different patterns may suggest can help you approach your results with greater confidence.

What Abnormal Liver Function Test Results May Indicate

Abnormal results do not automatically indicate a specific liver condition. Elevated liver enzymes — particularly ALT and AST — are among the most commonly seen abnormalities and can be influenced by a wide range of factors. Common patterns include:

Mildly elevated ALT or AST — May be associated with recent alcohol consumption, certain medications, intense physical exercise, or dietary factors. A single mild elevation is often temporary

Elevated GGT with other markers within range — May suggest recent alcohol intake or medication effects, particularly with drugs that affect the liver

Elevated ALP — May be associated with bile duct function or bone metabolism, and is sometimes elevated in isolation without liver significance

Elevated bilirubin — May suggest the liver is not processing waste products as efficiently as expected, or may be associated with conditions affecting red blood cell breakdown

Low albumin — May suggest reduced liver protein production, though it can also be influenced by nutritional status, kidney function or inflammatory conditions

For a broader understanding of how blood test results are interpreted, our guide on understanding blood test results provides helpful context across multiple marker types.

Temporary vs Persistent Elevations

A key distinction in liver function testing is whether abnormal values are temporary or persistent. Many factors can cause a transient elevation in liver enzymes:

Recent alcohol consumption

Intense physical exercise

Certain medications or supplements

Recent illness or infection

Dietary changes

A single set of mildly elevated results may not be cause for concern, particularly if an obvious temporary factor can be identified. However, persistently elevated markers on repeat testing may suggest ongoing liver stress and may indicate a need for medical advice from appropriate healthcare services.

Lifestyle Influences

Lifestyle plays a significant role in liver health. Alcohol consumption, diet, body weight, physical activity and medication use can all influence liver function test results. Understanding these connections can help you interpret your results in context and identify modifiable factors that may support improved liver health over time.

For more information on how lifestyle and liver health are connected, our article on liver health matters and what blood tests can reveal provides a comprehensive overview.

Monitoring Trends

As with most blood markers, tracking liver function results over time is far more informative than interpreting a single set of values. Establishing a baseline and monitoring trends helps identify whether markers are stable, improving or trending in a direction that may warrant further attention.

If inflammation is a concern alongside liver function, a C-reactive protein (CRP) test can provide additional insight into systemic inflammatory activity.

Why Do I Need a Liver Function Test?

There are several situations in which a liver function test may be particularly valuable:

Fatigue — Persistent tiredness that does not improve with rest may have multiple causes, and liver function is one area worth assessing. The liver plays a central role in energy metabolism, and impaired function can contribute to feelings of low energy

Medication monitoring — Many common medications are processed by the liver, and long-term use may affect liver enzyme levels. Regular testing can help monitor whether the liver is coping well with ongoing medication use

Alcohol intake — Alcohol is processed by the liver, and regular or heavy consumption can gradually affect liver health. Testing provides an objective measure of how alcohol intake may be influencing your liver markers

Digestive symptoms — Symptoms such as bloating, nausea, changes in stool colour or discomfort in the upper right abdomen may prompt investigation of liver and bile duct function

Preventive annual screening — Many health-conscious individuals choose to include liver function markers as part of a broader annual health check, even in the absence of symptoms

A health screening panel that includes liver function alongside other key markers provides a comprehensive picture of overall wellbeing. For the most thorough assessment, the Advanced Full Body MOT includes liver markers alongside a wide range of other health indicators. Our nurse-led service ensures your blood draw is carried out professionally and comfortably.

How to Prepare for a Liver Function Test

Preparing for a liver function test is straightforward and requires minimal adjustment to your usual routine.

Fasting

Fasting is not usually required for a standard liver function test. However, if your appointment includes other markers that require fasting — such as glucose or cholesterol — you may be asked to fast overnight. Water is always permitted and encouraged.

Avoiding Alcohol

Alcohol can directly affect liver enzyme levels, particularly GGT. For the most accurate results, it is advisable to avoid alcohol for at least 24 to 48 hours before your blood test. This helps ensure your results reflect your baseline liver function rather than the acute effects of recent alcohol consumption.

Medication Disclosure

Certain medications — including over-the-counter pain relievers, statins, antibiotics and herbal supplements — can influence liver enzyme levels. Informing the nurse-led team about any medications or supplements you are taking helps ensure your results are interpreted accurately.

Hydration

Staying well hydrated before your appointment makes the blood draw process smoother and more comfortable. Drinking water in the hours leading up to your test helps ensure your veins are accessible.

For detailed preparation guidance applicable to all blood tests, our article on preparing for a blood test covers everything you need to know. You can also review our blood test prices for transparent pricing on all available panels.

When Should Abnormal Results Be Reviewed?

Whilst a single mildly abnormal liver function result is common and often temporary, there are circumstances where further review is advisable.

Persistently Elevated Results

If repeat testing after an appropriate interval (typically 4 to 8 weeks) continues to show elevated liver enzymes or other abnormal markers, seeking medical advice from appropriate healthcare services is recommended. Persistent elevations may suggest ongoing liver stress that warrants further investigation.

Significantly Abnormal Values

If any marker is significantly above or below the reference range — rather than mildly elevated — seeking medical advice promptly is important. Significantly elevated liver enzymes, very low albumin, or markedly raised bilirubin may indicate a need for further assessment.

Accompanying Symptoms

If abnormal liver function results are accompanied by symptoms such as yellowing of the skin or eyes, persistent abdominal discomfort, unexplained weight loss, dark urine, or pale stools, seeking medical advice from appropriate healthcare services without delay is recommended. If symptoms are severe, accessing urgent medical care is important.

No Symptoms But Abnormal Results

Even in the absence of symptoms, abnormal liver function results should not be dismissed. The liver has a remarkable ability to continue functioning even when under significant stress, meaning symptoms may not appear until later stages. This is why regular monitoring through blood testing is so valuable — it can identify changes that would otherwise go unnoticed.

Frequently Asked Questions

What does a liver function test detect?

A liver function test detects changes in liver enzymes, proteins and bilirubin levels in your blood. These markers assess how well the liver is processing waste, producing proteins and managing bile flow. Abnormal levels may be associated with liver stress and can indicate a need for further monitoring or medical advice.

What is included in a liver panel blood test?

A standard liver panel typically includes ALT, AST, ALP, GGT, bilirubin, albumin and total protein. Together, these markers provide a comprehensive picture of liver enzyme activity, protein production and waste processing. Some panels may also include additional markers depending on the testing provider.

What is the reference range for ALT and AST?

The general UK reference range for ALT is approximately 7 to 56 U/L, and for AST approximately 10 to 40 U/L. These ranges may vary slightly between laboratories. Results that fall slightly outside the range may be influenced by temporary factors such as exercise, medication or recent alcohol consumption.

Can alcohol affect liver function test results?

Yes, alcohol can directly affect liver function test results, particularly GGT levels. Even moderate alcohol consumption in the days before testing can temporarily elevate liver enzymes. For the most accurate results, avoiding alcohol for at least 24 to 48 hours before your blood test is recommended.

How often should I check liver health?

For most adults, including liver function markers as part of an annual health screening is a practical approach. Those who take regular medications, consume alcohol frequently, or have a family history of liver conditions may benefit from more frequent testing — such as every 6 to 12 months — to monitor trends over time.

What happens if my liver function test is abnormal?

A single mildly abnormal result is common and often temporary. If results are persistently abnormal on repeat testing, or significantly outside the reference range, seeking medical advice from appropriate healthcare services is recommended. Tracking your results over time provides the most meaningful insight into your liver health.

This content has been reviewed for clinical accuracy by our laboratory team at Private Blood Tests London.

Conclusion

Your liver performs hundreds of essential functions every day, often without any outward signs of strain. A liver function test provides an objective, evidence-based window into how well this vital organ is working — measuring enzymes, proteins and waste products that together reveal a detailed picture of liver health.

Whether you are investigating symptoms, monitoring the effects of medication or lifestyle factors, or simply choosing to screen proactively as part of a broader health check, liver function testing is one of the most accessible and informative tools available. Tracking your results over time is particularly valuable, as it reveals trends that a single set of results cannot.

If you would like clarity on your liver health, you can arrange a liver function test appointment with Private Blood Tests London at a time that suits you. Visit https://www.privatebloodtestslondon.co.uk/book to book online.

This article is for general information only and does not replace professional medical advice.

What Does a Liver Function Test Detect? A Complete Guide to Liver Blood Markers