Complete Guide to Liver Function Tests (LFTs)

Quick answer

Liver function tests measure different enzymes that rise in different patterns: ALT and AST point to liver cell damage (hepatitis, fatty liver), while raised ALP with GGT points to bile duct blockage. The core takeaway: reading the pattern matters more than any single number, and mildly raised enzymes are common and often need watching rather than urgent action.

What each LFT measures

Test	Normal Range	What it reflects
ALT (Alanine aminotransferase)	7–56 U/L	Liver cell damage: most specific liver enzyme
AST (Aspartate aminotransferase)	10–40 U/L	Liver cell damage: also raised in muscle and heart disease
ALP (Alkaline phosphatase)	44–147 U/L	Liver or bile duct disease; bone disease
GGT (Gamma-GT)	Men: <71 U/L; Women: <42 U/L	Bile duct disease; alcohol use
Bilirubin (total)	0.1–1.2 mg/dL	Jaundice: from red cell breakdown or bile duct obstruction
Albumin	3.5–5.0 g/dL	Liver synthetic function: low in chronic liver disease
Total protein	6.3–8.2 g/dL	Combined albumin and globulin
INR / Prothrombin time	INR 0.8–1.2	Clotting factor production: impaired in severe liver disease

Key points

ALT and AST pattern means liver cell injury; ALP with GGT pattern means bile flow blockage.
Albumin and INR reflect the liver's synthetic function.
Mild ALT rises are common (fatty liver, alcohol, medicines) and often just need watching.
Raised enzymes need the pattern read, not a single number judged.

How to read your LFT pattern

Hepatocellular vs cholestatic pattern

Hepatocellular pattern (liver cell damage): ALT and AST raised much more than ALP. Causes: hepatitis (viral, alcoholic, autoimmune), fatty liver disease, paracetamol overdose. Cholestatic pattern (bile duct obstruction): ALP and GGT raised more than ALT and AST. Causes: gallstones, bile duct cancer, primary biliary cholangitis. Mixed pattern: both groups raised, seen in severe hepatitis or drug reactions.

What does a raised ALT mean?

ALT is the most liver-specific enzyme. Causes of raised ALT by level: mild (1–3x normal): fatty liver (NAFLD), alcohol, medications, thyroid disease; moderate (3–10x): hepatitis B or C, drug-induced liver injury, autoimmune hepatitis; severe (>10x): acute viral hepatitis, ischaemic hepatitis ("shock liver"), paracetamol overdose, acute biliary obstruction. Isolated mild ALT elevation (1–2x normal) is very common and often from fatty liver.

LFT checklist for patients

Questions to discuss with your doctor

Which tests are abnormal: liver enzymes or liver function?
Is the pattern hepatocellular or cholestatic?
Do I need a liver ultrasound?
Should alcohol or medication be reviewed?
Do I need tests for hepatitis B or C?
Should I lose weight to help a fatty liver?

ALT versus ALP, two different patterns of liver injury

Liver function tests (LFTs) include multiple enzymes that rise in different clinical situations. Understanding which enzyme pattern is elevated guides diagnosis efficiently:

Hepatocellular pattern (ALT and AST predominant): ALT (alanine aminotransferase) and AST (aspartate aminotransferase) are enzymes inside liver cells (hepatocytes). They leak into the blood when hepatocytes are damaged or dying. A predominantly elevated ALT/AST points to hepatocellular injury: viral hepatitis (hepatitis B and C), alcohol-related hepatitis, drug-induced liver injury (paracetamol overdose, statins, isoniazid), non-alcoholic steatohepatitis (NASH, more common with obesity),³ or ischaemic hepatitis ("shock liver").² ALT is more liver-specific; AST is also found in muscle and heart. An AST:ALT ratio above 2:1 suggests alcohol-related hepatitis (alcohol impairs pyridoxal phosphate, which favours AST over ALT production).
Cholestatic pattern (ALP and GGT predominant): Alkaline phosphatase (ALP) and GGT are enzymes expressed in bile duct cells. They rise when bile cannot flow normally, biliary obstruction. Causes include gallstones in the common bile duct, bile duct strictures, pancreatic head cancer, primary biliary cholangitis (PBC), and primary sclerosing cholangitis (PSC). ALP also rises from bone (Paget's disease, metastases, growing bones in children), GGT is used to confirm the ALP is liver-derived rather than bone-derived.

Albumin and INR, synthetic function markers

ALT and ALP measure liver damage; albumin and prothrombin time (PT/INR) measure liver function, what the liver is actually producing. These markers are critical in assessing the severity of liver disease:

Albumin: The main protein synthesised exclusively by the liver. Half-life approximately 20 days, so albumin falls only in more prolonged liver dysfunction. Serum albumin below 35 g/L indicates impaired synthetic function; below 25 g/L is severe hypoalbuminaemia with risk of oedema and ascites. Important caveat: albumin is a negative acute phase reactant, it falls in any inflammatory state, not just liver disease.
Prothrombin time (PT) / INR: The liver synthesises clotting factors (I, II, V, VII, IX, X). A prolonged PT/INR in the context of liver disease indicates failing synthetic function. This is the most sensitive early marker of acute liver failure, rising INR alongside jaundice and confusion (encephalopathy) defines acute liver failure and triggers urgent transplant assessment (King's College criteria).

The Child-Pugh score and MELD (Model for End-Stage Liver Disease) score, both incorporating bilirubin, albumin, and INR, are used to stage chronic liver disease severity and prioritise patients for liver transplantation.

Your next steps for an abnormal LFT

Separate enzymes from function
ALT, AST, ALP and GGT measure damage; albumin and INR measure what the liver actually produces. Work out which group is abnormal — they answer different questions.
Read the pattern, not the single number
ALT and AST raised much more than ALP means a hepatocellular pattern (liver cell injury); ALP and GGT raised more than ALT and AST means a cholestatic pattern (bile flow blockage). The pattern directs everything that follows.
Bring a complete medicine and supplement list
Mild ALT rises are commonly explained by medicines, herbal supplements, alcohol or a recent illness. Your doctor needs the full list to interpret the result.
Retest a mild rise before worrying
Mild ALT elevations (1–3 times normal) from fatty liver, alcohol or medicines often just need watching. A repeat test after a few weeks shows whether it is persistent or passing.
Ask what comes next
A persistent abnormal pattern may lead to a liver ultrasound, hepatitis B and C testing, or a review of alcohol use. Ask which applies to your pattern.

What each LFT measures at a glance

A liver panel bundles 6–8 measurements, each telling a different story. This table compiles them; the article explains how to read their patterns together.

Test	Normal range	What it reflects
ALT	7–56 U/L	Liver cell damage; the most liver-specific enzyme
AST	10–40 U/L	Liver cell damage; also raised in muscle and heart disease
ALP	44–147 U/L	Liver or bile duct disease; also bone disease
GGT	Men <71, women <42 U/L	Bile duct disease; sensitive to alcohol use
Bilirubin (total)	0.1–1.2 mg/dL	Jaundice marker; from red cell breakdown or bile blockage
Albumin	3.5–5.0 g/dL	Liver synthetic function; low in chronic liver disease
Total protein	6.3–8.2 g/dL	Albumin plus globulin combined
INR	0.8–1.2	Clotting factor production; impaired in severe liver disease

Practical notes

Avoid alcohol for at least 24–48 hours before the test and tell the lab about any recent drinking. Ask whether to fast — many labs prefer 8 hours — and disclose all medicines, herbal products, and supplements, since the liver processes most of them and several can raise enzymes.

Bring your medicine and supplement list (including paracetamol use, statins, and herbal or Ayurvedic products), a note of any recent illness — viral fevers can transiently raise enzymes — and past LFT reports for comparison.

An LFT is a panel, and patterns matter: which enzymes are raised and by how much, alongside bilirubin and albumin. A mildly raised ALT after an illness or a heavy weekend often just needs a recheck on your doctor's judgment — one panel rarely settles anything alone.

For follow-up, ask when to repeat the panel, under what conditions (same lab, fasting, an alcohol-free interval), and what symptoms — jaundice, dark urine, persistent fatigue, abdominal pain — should bring you back sooner.

In India

A liver function test panel is typically ₹600–₹1,400, though prices vary by city and lab. If a recheck is planned, ask whether the lab offers a lower follow-up rate for repeating the same panel.

Choose NABL-accredited labs; home sample collection is available in major cities. The reference range printed on your own report is the one that counts — methods and ranges differ between labs, so do not compare your values against a generic online table.

Frequently Asked Questions

What do liver function tests actually measure?

They combine enzymes that leak from damaged liver cells or bile ducts (ALT, AST, ALP, GGT) with bilirubin and albumin that reflect how well the liver is working. Together the panel gives a picture of liver health — damage markers and function markers answering different questions.

Can liver tests be abnormal without liver disease?

Yes. Vigorous exercise, some medications, alcohol and even muscle injury can move these results. That is why the pattern across the enzymes and a repeat test matter far more than any single value taken on its own.

What does a raised ALT and AST indicate?

Raised ALT and AST usually reflect liver cell injury — from causes such as fatty liver, viral hepatitis, alcohol or medications. ALT is the more liver-specific of the two. The ratio between them, and how they compare with ALP and GGT, helps narrow down the cause.

My ALT is slightly high but I feel fine — what should I do?

Mild, isolated rises are common and often transient — recent alcohol, a viral illness, strenuous exercise, or certain medicines can all cause them. Do not self-treat; bring the report to your doctor, who will usually suggest a recheck after an alcohol-free interval and review your medicines.

I take herbal supplements — do I need to mention them?

Yes, always. ‘Natural’ does not mean liver-neutral — several herbal and Ayurvedic products are known to affect liver enzymes. List everything you take, including doses and brands, so your doctor can spot a possible link.

Does fatty liver always show up on an LFT?

Not always. Early fatty liver can exist with normal enzymes, which is why doctors sometimes add an ultrasound or other checks when risk factors such as weight, diabetes, or lipid levels suggest it. Ask your doctor whether your LFT alone answers the question for you.

How long after drinking should I wait before an LFT?

Ask the lab or your doctor — a common practical answer is at least a couple of alcohol-free days before the draw, since recent drinking can raise enzymes and muddy the baseline. Tell them honestly about recent intake so the result is interpreted correctly.

References

Sources cited on this page. PubMed links open the original abstract.

Pratt DS, Kaplan MM. Evaluation of abnormal liver-enzyme results in asymptomatic patients. N Engl J Med. 2000;342(17):1266–1271. PMID 10781624 · doi:10.1056/NEJM200004273421707
Sulava E, Tran D, Nohrenberg C, Koyfman A, Long B. "Elevated Liver Enzymes: Emergency Department-Focused Management." J Emerg Med. 2017;52(5):654–667. PMID 27889359 · doi:10.1016/j.jemermed.2016.10.016
Li W, Tyrrell J, Wood AR, et al. "Obesity Predicts Liver Function Testing and Abnormal Liver Results." Obesity (Silver Spring). 2020;28(1):132–138. PMID 31804018 · doi:10.1002/oby.22669

Medical Disclaimer: For educational purposes only. Always consult a qualified healthcare professional for diagnosis and treatment.