What Does a Liver Function Test Show and When Should You Get One?

What Is a Liver Function Test?

A liver function test, abbreviated as LFT and sometimes called a liver blood test or hepatic panel, is a panel of blood measurements that assesses the health and functional capacity of the liver. The liver performs over 500 distinct functions in the body, including filtering toxins from the blood, producing bile for digestion, manufacturing proteins that enable blood clotting, metabolising drugs and alcohol, and storing glycogen, vitamins, and minerals. When liver cells are damaged or the organ is under stress, it releases certain enzymes into the bloodstream and changes the levels of proteins and waste products that a blood test can detect.

The LFT is one of the most frequently ordered blood tests in UK general practice. According to Lab Tests Online UK, liver blood tests are requested to assess liver health and help detect, monitor, or investigate conditions such as liver disease, inflammation, or damage. The test requires a single blood draw from a vein in the arm and in most cases does not require fasting, making it a straightforward and accessible investigation.

A standard LFT measures several markers simultaneously: alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), gamma-glutamyl transferase (GGT), bilirubin, albumin, and total protein. Some panels also include prothrombin time, which measures the liver’s ability to produce clotting factors. Each of these markers tells a different part of the story about liver health, and clinicians interpret them together rather than in isolation.

What Does a Liver Function Test Show? Each Marker Explained

Understanding what each LFT marker measures gives you the ability to read your results with context rather than anxiety. The key is to look at the pattern of results across all markers, not to focus on a single value that sits slightly outside the reference range.

Alanine Aminotransferase (ALT)

ALT is an enzyme found primarily in liver cells. When liver cells are damaged or inflamed, they release ALT into the bloodstream, raising its concentration. ALT is considered the most liver-specific enzyme on the standard LFT panel, meaning a raised ALT most reliably points to the liver rather than other organs. Common causes of elevated ALT include non-alcoholic fatty liver disease (NAFLD), alcohol-related liver damage, viral hepatitis, and the effects of certain medications. A mild elevation is often the first measurable sign of liver stress, sometimes appearing years before any symptoms develop.

Aspartate Aminotransferase (AST)

AST is an enzyme present in the liver but also found in the heart, kidneys, pancreas, and skeletal muscle. Because it is less liver-specific than ALT, clinicians often look at the ratio of AST to ALT rather than either value alone. When AST is elevated to a greater degree than ALT, this pattern commonly suggests alcohol-related liver injury. When ALT is elevated more than AST, non-alcoholic causes such as fatty liver disease or viral hepatitis are more likely. An AST level more than twice the upper limit of normal warrants prompt clinical review.

Alkaline Phosphatase (ALP)

ALP is an enzyme found in the liver, bile ducts, and bones. Elevated ALP on a liver panel most commonly indicates a problem with bile flow, a condition called cholestasis, where bile is not draining properly through the bile ducts. This can occur due to gallstones, bile duct blockages, or certain liver conditions. It is important to note that ALP is also naturally elevated in children due to bone growth and in pregnant women due to placental production. An isolated ALP elevation in adults with normal other liver markers may prompt a check of bone health and vitamin D levels rather than focusing solely on the liver.

Gamma-Glutamyl Transferase (GGT)

GGT is particularly sensitive to alcohol intake and is one of the first markers to rise with regular or heavy drinking. Even moderate consistent alcohol consumption can push GGT above the normal range, making it a useful indicator of alcohol-related liver stress before other markers become abnormal. GGT is also elevated in other liver conditions and can rise with certain medications. When GGT and ALP are both raised together, this pattern strongly suggests a problem with bile flow or the biliary system. For professional drivers undergoing a D4 medical or occupational health assessment, GGT results can form part of the broader metabolic health picture reviewed during the examination.

Bilirubin

Bilirubin is a yellowish waste product formed when old red blood cells are broken down. The liver processes bilirubin and excretes it through bile into the digestive system. When bilirubin accumulates in the blood above normal levels, it causes jaundice, the visible yellowing of the skin and whites of the eyes. Raised bilirubin can reflect several different problems: the liver may not be processing bilirubin efficiently, bile flow may be obstructed, or red blood cells may be breaking down too rapidly. A mildly elevated bilirubin with otherwise normal LFT results is frequently caused by Gilbert’s syndrome, a benign inherited condition affecting approximately 5 to 10 percent of the UK population that is harmless and requires no treatment.

Albumin

Albumin is a protein manufactured exclusively by the liver. It performs critical functions including maintaining fluid balance between blood vessels and surrounding tissues and transporting hormones, vitamins, and drugs through the bloodstream. Because albumin is only made by the liver, a low albumin level indicates that the liver’s protein-producing capacity has been compromised. This is typically a feature of chronic or advanced liver disease rather than acute injury, as albumin levels fall slowly over time. Low albumin can also result from severe malnutrition or from kidney disease, where albumin is lost in urine rather than produced in reduced amounts.

First Medical Consultants includes albumin as a core component of its private blood testing packages, alongside liver enzymes, cholesterol, and kidney function markers, giving you a comprehensive view of organ health in a single appointment.

Total Protein

Total protein measures the combined concentration of albumin and globulins in the blood. Globulins include antibodies and other immune proteins not made solely by the liver. Abnormal total protein results can reflect liver disease, kidney dysfunction, nutritional deficiency, or immune system conditions. Clinicians interpret total protein alongside albumin to understand whether a low result reflects reduced liver production or loss through another route such as the kidneys or the gut.

What Conditions Can a Liver Function Test Help Detect?

The LFT is a broad screen rather than a specific diagnostic test. It identifies patterns of abnormality that direct further investigation. The conditions and clinical situations where LFT results most commonly provide actionable information include:

• Non-alcoholic fatty liver disease (NAFLD): now affecting an estimated 25 to 30 percent of the UK adult population, often detected through raised ALT with few or no symptoms
• Alcohol-related liver disease: suggested by elevated GGT and an AST-to-ALT ratio greater than 2:1
• Viral hepatitis (A, B, and C): produces significantly raised ALT and AST during active infection
• Bile duct obstruction: identified by elevated ALP and GGT, often alongside raised bilirubin
• Cirrhosis: advanced scarring of the liver, reflected in low albumin, raised bilirubin, and prolonged clotting times
• Drug-induced liver injury: certain medications including statins, paracetamol in high doses, and some antibiotics can raise liver enzymes
• Autoimmune liver conditions: such as primary biliary cholangitis or autoimmune hepatitis, which produce specific patterns of enzyme elevation
• Monitoring known liver disease: serial LFTs track whether a condition is stable, improving, or worsening over time

When Should You Get a Liver Function Test?

Liver disease is sometimes called a silent condition because many people experience no obvious symptoms during the early stages. By the time symptoms appear, damage has often been present for years. This makes proactive LFT screening particularly valuable for anyone in a higher-risk category.

You should consider booking a liver function test if you experience any of the following symptoms without a clear explanation:

• Yellowing of the skin or whites of the eyes (jaundice)
• Persistent unexplained fatigue or weakness
• Pain or discomfort in the upper right side of the abdomen
• Dark-coloured urine or unusually pale stools
• Nausea, loss of appetite, or unintended weight loss
• Swelling in the abdomen, legs, or ankles
• Itchy skin without an obvious dermatological cause
• Easy bruising or bleeding more than expected from minor injuries

Beyond symptoms, an LFT is appropriate if you fall into any of these background risk categories:

• Regular or heavy alcohol consumption
• Long-term use of medications known to affect the liver, including statins, methotrexate, or certain antifungal drugs
• Known or suspected exposure to hepatitis B or C
• A family history of liver disease
• Obesity or type 2 diabetes, both of which significantly raise the risk of NAFLD
• Use of high-dose nutritional supplements, herbal products, or performance-enhancing substances
• Occupational exposure to chemicals or solvents that are processed by the liver

Many people also include an LFT as part of a routine annual health MOT, especially from the age of 35 onwards. Catching an elevated ALT or GGT at a mildly raised level gives you and your clinician time to investigate causes and make lifestyle adjustments before the liver sustains significant damage. For a broader overview of what private health screening involves and which panels are available, visit the First Medical Consultants private blood tests guide.

Does a Liver Function Test Require Fasting?

A standalone liver function test does not require fasting because the key markers, ALT, AST, ALP, GGT, bilirubin, and albumin, are not significantly affected by eating or drinking in the hours before the test. However, if your LFT is being ordered alongside tests that do require fasting, such as a fasting glucose or a full lipid panel, your clinician will advise fasting for the entire appointment to avoid skewing those additional results. When in doubt, check with your clinic at the time of booking. It is always beneficial to drink plenty of water before a blood draw to make veins easier to access and reduce discomfort during the procedure.

Alcohol consumption can directly raise GGT and ALT in the days following heavy intake. If you drink regularly, it is worth avoiding alcohol for at least 48 to 72 hours before your LFT appointment to get a clearer baseline reading that reflects your liver health rather than a temporary post-drinking spike.

What Happens After a Liver Function Test?

If your LFT results are entirely within the normal reference range, this is reassuring, though it does not guarantee the absence of all liver conditions. Some early-stage liver conditions can exist with normal enzyme levels, particularly if damage is not yet causing significant cell breakdown or if the liver retains enough functional reserve to keep levels within range.

If one or more markers are mildly elevated, your clinician will typically recommend repeating the test after a defined interval, often four to six weeks, to determine whether the elevation is persistent or transient. A single mildly raised result often resolves without intervention. Persistent elevation, or any result more than three times the upper limit of normal, will usually prompt further investigation. This may include an abdominal ultrasound scan, additional blood tests to check for viral hepatitis or autoimmune markers, or a referral to a hepatologist (liver specialist). Taxi drivers and HGV operators who have liver-related findings as part of their fitness review can find relevant guidance on how medical conditions interact with licensing requirements through the taxi medical page.

Frequently Asked Questions About Liver Function Tests

Book a Private Liver Function Test With First Medical Consultants

First Medical Consultants provides private blood testing including liver function panels across the UK, with clinics in Manchester, Birmingham, Liverpool, Wolverhampton, Stoke-on-Trent, and more. Appointments are available seven days a week including evenings and weekends, with no GP referral required. Our GMC-registered doctors and qualified phlebotomists deliver accurate, confidential results in a professional clinical environment.

The liver function test is available as a standalone panel or as part of our comprehensive health screening packages, which combine liver, kidney, cholesterol, full blood count, and additional markers into a single appointment. To explore which package suits your health goals, visit our private blood testing page or call 0331 6300 850.