What an LFT Actually Measures
A liver function test — usually written as LFT on Australian pathology reports — is not really one test, but a panel of six to seven markers measured together: ALT, AST, GGT, ALP, total bilirubin, albumin, and often total protein. Together they reveal three different things about your liver: how damaged the cells are (the enzymes), how well bile is flowing (ALP and GGT), and how well the liver is doing its synthetic job (albumin and protein).
The LFT is one of the most-ordered blood tests in Australia — about 15 million LFTs are processed each year across the public and private pathology systems. Many of those uncover abnormalities, most of which turn out to be benign and reversible. Knowing what each marker means saves you from unnecessary worry and points you to the right lifestyle change.
The Six (or Seven) Markers in Plain English
| Marker | What it is | Australian normal range (adult) |
|---|---|---|
| ALT (Alanine aminotransferase) | Enzyme leaked when liver cells are damaged. The most liver-specific marker. | <40 U/L (men), <35 U/L (women) |
| AST (Aspartate aminotransferase) | Enzyme from liver, heart and muscle. Used together with ALT to spot patterns. | <40 U/L |
| GGT (Gamma-glutamyl transferase) | Bile-duct enzyme. Most sensitive to alcohol and certain medications. | <60 U/L (men), <40 U/L (women) |
| ALP (Alkaline phosphatase) | From liver bile ducts and bone. Raised in bile obstruction or rapid bone turnover. | 30–110 U/L (higher in growing children, pregnancy) |
| Bilirubin (total) | Pigment from broken-down red blood cells, processed by the liver. | <20 µmol/L |
| Albumin | Main blood protein, made only by the liver. Reflects synthetic function. | 35–50 g/L |
| Total protein | Albumin plus globulins. Often included for context. | 60–80 g/L |
Reference ranges vary slightly between Australian labs (Sullivan Nicolaides, Dorevitch, Laverty, Australian Clinical Labs all use the same RCPA-aligned standards but report a small variation depending on assay platform). Always read the range printed on your own pathology report.
The Three Most Common Abnormal Patterns
1. Mildly raised ALT (and sometimes AST) — the "fatty liver pattern"
By far the most common abnormal LFT in Australian general practice. ALT sits at 40–120 U/L, AST is normal or mildly raised, GGT is often mildly raised, ALP and bilirubin are normal. The AST:ALT ratio is <1.
Most likely cause: non-alcoholic fatty liver disease (NAFLD/MAFLD). Now affects approximately 1 in 3 Australian adults, driven by central obesity, type 2 diabetes, and dyslipidaemia. It is the leading cause of liver transplant referral in patients under 50.
What to do: repeat the LFT in 4–6 weeks. If still raised, the RACGP recommends an abdominal ultrasound, fasting lipids, HbA1c, and a hepatitis B/C screen. Lifestyle alone (7–10% weight loss, alcohol-free, regular exercise) normalises ALT in around 60% of cases within 6 months.
2. Raised GGT alone — the "alcohol or medication pattern"
GGT is more sensitive to alcohol than any other liver enzyme. Even moderate drinking — 5–10 standard drinks per week — can push GGT above the upper limit. Common medication causes: anticonvulsants (phenytoin, carbamazepine), NSAIDs taken regularly, statins (uncommon but possible), and some antifungals.
What to do: a 4-week alcohol-free trial and a repeat test is the standard first step. If GGT does not fall, or if it is more than 3× the upper limit, your GP will usually order an abdominal ultrasound and check ALP — together they can flag bile duct obstruction or pancreatic disease.
3. Raised ALP and GGT together — the "bile duct pattern"
When ALP and GGT both rise but ALT and AST stay normal, the issue is usually with bile flow rather than the liver cells themselves. Common causes: gallstones blocking the common bile duct, primary biliary cholangitis, certain medications, and rarely pancreatic head tumours.
What to do: this combination always warrants imaging — typically a liver ultrasound first, then MRCP if the ultrasound is inconclusive. Do not wait for symptoms; bile duct obstruction can become urgent quickly.
What Severe LFT Elevations Mean
The thresholds change at the high end:
- ALT > 5× upper limit (over ~200 U/L): consider acute viral hepatitis (A, B, E in Australia), drug-induced liver injury (paracetamol overdose is the most common cause in Australian hospitals), autoimmune hepatitis, or ischaemic injury. Always needs same-day or next-day GP review.
- ALT > 1000 U/L: usually paracetamol toxicity, severe ischaemic hepatitis, or acute viral hepatitis. This is an emergency — present to ED.
- Bilirubin > 50 µmol/L without obvious cause: warrants urgent GP review. Visible jaundice usually appears at bilirubin > 40 µmol/L.
- Albumin < 30 g/L on a stable patient: indicates significant chronic liver disease, kidney disease (nephrotic syndrome) or severe inflammation. Needs investigation, not just observation.
The AST:ALT Ratio — A Free Bonus Diagnostic
Both ALT and AST appear on every Australian LFT, so the ratio is yours for free:
- AST:ALT < 1 (ALT higher than AST): typical of fatty liver, viral hepatitis, drug-induced injury.
- AST:ALT > 2 with both raised: classic alcoholic liver disease pattern.
- Isolated AST elevation, ALT normal: usually muscle source — recent heavy exercise, statin-related myopathy, hypothyroidism. Repeat after 7 days of rest before assuming liver involvement.
What Affects LFT Accuracy
An abnormal LFT does not always mean liver disease. Things that can transiently move the numbers:
- Recent heavy exercise — raises AST (and creatine kinase) for 2–7 days. Repeat the test after a rest week.
- Recent paracetamol use — even normal doses can briefly nudge ALT.
- Pregnancy — ALP rises (placental contribution); other enzymes typically stay in range.
- Time of day and fasting status — most labs do not require fasting for an LFT, but morning samples are slightly more standardised.
- Recent supplement use — green tea extract, kava, comfrey, and several bodybuilding supplements are documented hepatotoxins in Australia.
Tracking LFTs Over Time
An LFT result in isolation is much less informative than a series. The Liver Foundation Australia and the RACGP both recommend retesting in 4–6 weeks for any new mildly abnormal result, and every 6 months for known fatty liver. Most Australian pathology portals show only your latest few values — uploading every PDF to a long-range tracker like BloodTrack lets you see whether ALT is drifting up or down across years, and whether it correlates with weight, alcohol intake, or new medications.
Bottom Line
Most abnormal LFTs in Australia are mild, reversible, and lifestyle-related. Repeat in 4–6 weeks, look at the pattern (which enzymes are raised together), and use the AST:ALT ratio as a free diagnostic. Severe elevations (>3× the upper limit, or any elevation with jaundice) need same-day GP review.