Understanding Your Liver Function Test Results: ALT, AST, ALP and GGT Explained

Your doctor has ordered liver function tests — or you have received results with abbreviations like ALT, AST, ALP, GGT, and bilirubin, and you are not sure what any of it means. You are not alone. Liver function tests are among the most commonly ordered blood panels, yet the results are rarely explained clearly in a busy clinical appointment.

This plain-English guide breaks down what each marker measures, what high or low results typically mean, and the questions you should ask your doctor at your follow-up.

What Are Liver Function Tests?

Liver function tests (LFTs) — also called a liver panel or hepatic function panel — are a group of blood tests that measure enzymes, proteins, and substances produced or processed by the liver. They are ordered to screen for liver disease, monitor known liver conditions, check medication side effects, or investigate symptoms such as fatigue, abdominal pain, jaundice, or nausea.

One important caveat: despite the name, LFTs do not directly measure how well your liver is functioning in most cases. They detect liver cell damage or obstruction to bile flow. True liver function is assessed by specific tests like prothrombin time (PT) and albumin levels.

The Key Liver Markers Explained

ALT — Alanine Aminotransferase

What it is: An enzyme found mainly in liver cells. When liver cells are damaged or inflamed, ALT leaks into the blood.

Normal range: Approximately 7–56 U/L (varies by lab and gender — men typically have slightly higher upper limits)

High ALT means: Liver cell injury. Common causes include fatty liver disease (NAFLD), alcohol-related liver damage, hepatitis B or C, certain medications (paracetamol, statins, some antibiotics), or autoimmune hepatitis.

Mildly elevated (1–3× upper limit): Often from fatty liver or medication. Your doctor will likely monitor and retest.

Significantly elevated (5×+ upper limit): Suggests active liver inflammation — requires prompt investigation.

AST — Aspartate Aminotransferase

What it is: An enzyme found in the liver, but also in heart muscle, skeletal muscle, and red blood cells. Less liver-specific than ALT.

Normal range: Approximately 10–40 U/L

High AST means: Liver damage, but also muscle injury, heart attack, or haemolysis (red blood cell breakdown). Always interpreted alongside ALT.

AST:ALT ratio: If AST is roughly twice as high as ALT, this pattern often suggests alcohol-related liver disease. If ALT is higher than AST, fatty liver is more likely.

ALP — Alkaline Phosphatase

What it is: An enzyme found in the liver, bile ducts, and bones. High ALP points to either a bile duct problem or a bone condition.

Normal range: Approximately 44–147 U/L (higher in children and pregnant women — bone growth and placenta produce ALP)

High ALP means: Bile duct blockage (gallstones, tumour, primary biliary cholangitis), liver infiltration, or bone disease (Paget’s disease, bone metastases). Your doctor will usually check GGT alongside to help determine whether the source is the liver or the bone.

GGT — Gamma-Glutamyl Transferase

What it is: An enzyme that is highly sensitive to alcohol intake and bile duct disease. Raised GGT with raised ALP almost always points to a liver or bile duct source.

Normal range: Approximately 9–48 U/L (men tend to run higher)

High GGT means: Alcohol use (even moderate regular drinking elevates GGT), bile duct obstruction, fatty liver disease, or certain medications. GGT is the most sensitive marker for alcohol-related liver change — it can be raised even before other liver markers are abnormal.

Bilirubin

What it is: A yellow pigment produced when red blood cells break down. The liver processes bilirubin and excretes it in bile. Elevated bilirubin causes jaundice (yellowing of skin and eyes).

Normal range: Total bilirubin approximately 3–20 µmol/L (varies by lab)

High bilirubin means: The liver cannot process bilirubin fast enough (liver disease, bile duct blockage) or red blood cells are breaking down too fast (haemolysis). Gilbert’s syndrome — a benign genetic condition — causes mildly elevated bilirubin with no other abnormalities and no treatment needed.

Albumin

What it is: The main protein produced by the liver. Unlike the enzymes above, albumin reflects actual liver function — a healthy liver makes plenty of albumin; a damaged liver makes less.

Normal range: Approximately 35–50 g/L

Low albumin means: Chronic liver disease (cirrhosis), malnutrition, kidney disease (protein loss in urine), or severe inflammation. A low albumin in the context of liver disease is a serious finding indicating the liver is struggling to maintain its synthetic function.

What Causes Abnormal Liver Function Tests?

The most common causes of mildly abnormal LFTs seen in routine blood tests:

• Non-alcoholic fatty liver disease (NAFLD) — the single most common cause in most countries, driven by excess weight, insulin resistance, and poor diet
• Alcohol — even without alcohol dependence, regular heavy drinking raises GGT and can raise ALT/AST
• Medications — statins, paracetamol (especially at high doses or with alcohol), NSAIDs, some antibiotics, and herbal supplements can cause transient or persistent LFT elevation
• Viral hepatitis — hepatitis B and C often cause significant ALT/AST elevation
• Thyroid disease — both hypothyroidism and hyperthyroidism can affect liver markers
• Coeliac disease — an underrecognised cause of mildly elevated LFTs

7 Questions to Ask Your Doctor About Your Liver Results

1. Which markers are elevated, and by how much above the upper limit of normal? Context matters — 1.5× is very different from 10× the upper limit.
2. Is this a new finding or have my LFTs been elevated before? A trend matters more than a single abnormal result.
3. Could any of my current medications be causing this? Ask about both prescription and over-the-counter drugs, including supplements.
4. Do I need additional tests — ultrasound, hepatitis screen, or autoimmune markers?
5. Should I avoid alcohol completely until this is investigated?
6. At what point would you consider referring me to a liver specialist (hepatologist)?
7. When should I repeat the test, and what result would reassure you?

Useful Tools for Managing Your Health Records

Keeping your blood test results organised makes it much easier to track trends over multiple appointments.

Doctor Appointment Journal — a structured notebook for logging test results, doctor notes, and follow-up questions. Useful for anyone managing ongoing investigations across multiple appointments.

Validated Home Blood Pressure Monitor — high blood pressure is linked to metabolic syndrome, which often accompanies fatty liver disease. Monitoring at home keeps your doctor informed between visits.

ASEAN Readers — Shop Locally

If you are based in Singapore or Southeast Asia, these local options may be more convenient:

Watsons Singapore — Vitamins & Supplements — liver support supplements, omega-3, and general wellness products available in-store and online across Singapore and Southeast Asia.

Health Monitoring Devices on Shopee SG — blood pressure monitors and other tools useful for patients managing metabolic conditions linked to liver health.

Disclosure: DoctorVisitPrep.com participates in affiliate programmes. Clicking these links may earn a small commission at no extra cost to you.

Disclosure: As an Amazon Associate, DoctorVisitPrep.com earns from qualifying purchases. This does not affect which products are recommended.

Key Takeaway

Abnormal liver function tests are common and, in most cases, mildly elevated results from a single blood draw are investigated rather than acted on immediately. The critical thing is not to ignore them. Bring your printed results to your follow-up, ask which markers are elevated and by how much, and ask what the next step is — whether that is a repeat test, an ultrasound, a medication review, or a specialist referral. The earlier liver disease is caught, the more reversible it tends to be.

This article is for preparation purposes only and does not constitute medical advice. Always follow the guidance of your treating doctor.