If your doctor has ordered liver function tests — often abbreviated to LFTs — your report will come back with a cluster of numbers that can look intimidating. In reality, most of them are measuring just two things: how well your liver is working, and whether any of its cells are under stress.
This guide explains what each value on a typical liver panel means, what can push the numbers up or down, and when a result is genuinely worth following up. As always, your own doctor is the right person to interpret your results in the context of your health.
What liver function tests actually measure
Despite the name, LFTs don't measure a single 'function'. They combine two kinds of markers: enzymes that leak into the blood when liver cells are irritated or damaged, and substances the liver makes or clears that show how well it's doing its job.
ALT and AST: the enzymes that flag cell stress
ALT (alanine aminotransferase) and AST (aspartate aminotransferase) live inside liver cells. When those cells are inflamed or injured, the enzymes spill into the bloodstream and the numbers rise. ALT is fairly specific to the liver; AST is also found in muscle and the heart, so a raised AST isn't always about the liver.
Mild elevations are common and often harmless — they can follow a viral illness, a night of drinking, intense exercise or certain medications. Persistently high or very high levels are what prompt a closer look.
ALP and GGT: the bile-flow markers
ALP (alkaline phosphatase) and GGT (gamma-glutamyl transferase) tend to rise when bile flow out of the liver is blocked or slowed — for example by gallstones or a duct problem. ALP also comes from bone, so it can be raised for reasons unrelated to the liver. GGT helps sort this out: if both ALP and GGT are up, the liver or bile ducts are the likely source.
Bilirubin: the pigment behind jaundice
Bilirubin is a yellow waste product from the normal breakdown of red blood cells; a healthy liver processes and clears it. When bilirubin builds up, it can tint the skin and the whites of the eyes yellow — the classic sign of jaundice. A raised bilirubin can point to the liver, the bile ducts or faster-than-normal red-cell breakdown, so it's always read alongside the other markers.
Albumin and total protein: the 'is it working' markers
Albumin is a protein the liver manufactures. A steady, normal albumin level is reassuring — it suggests the liver has been doing its synthetic work over recent weeks. A low albumin can reflect long-standing liver problems, but also poor nutrition, kidney issues or inflammation, so it isn't liver-specific either.
Why a single abnormal number isn't a diagnosis
Liver markers move for all sorts of everyday reasons, and one out-of-range value on its own rarely means disease. Doctors look at the pattern — which markers are up, by how much, and whether the picture is hepatocellular (ALT/AST-led) or cholestatic (ALP/GGT-led) — and they repeat the test to see whether it's a blip or a trend.
- A mildly raised ALT that returns to normal on a repeat test is usually nothing to worry about
- A rising trend over several tests matters more than one high reading
- Medications, alcohol and recent illness are common, benign causes
- Very high levels, or jaundice, warrant prompt medical review
What to do with your results
Keep every liver panel in one place so you and your doctor can see the trend rather than an isolated snapshot. If you track your lab results over time, a gradual change becomes obvious long before any single value looks alarming. Bring your history to your appointment, note any new medications or supplements, and ask specifically which pattern your doctor is seeing and what, if anything, needs rechecking.