alanine aminotransferase · ALT/SGPT · liver enzyme
ALT: what a raised liver enzyme means
ALT is an enzyme that lives inside liver cells. Finding a lot of it in your blood means liver cells have been leaking — it says that something is irritating the liver, never what.
What it measures
Alanine aminotransferase is concentrated in liver cells. When those cells are inflamed or injured it escapes into the blood, so the level is an indirect measure of ongoing liver-cell injury. It is a marker of irritation, not of how well the liver is working — that is what albumin, bilirubin and clotting show.
Why it gets tested
As part of a routine liver panel, to investigate fatigue, abdominal pain or jaundice, to monitor medication known to affect the liver, and to follow up an abnormal earlier result. It is also checked in anyone with risk factors for fatty liver — higher weight, type 2 diabetes, high triglycerides — or for viral hepatitis.
Typical ranges
Commonly printed as up to about 40 U/L, though many laboratories now use lower, sex-specific limits — around 33 U/L for men and 25 U/L for women — because the older ranges were drawn from populations full of undiagnosed fatty liver. Yours may use either, which makes this one of the places the printed range matters most.
Compare against the range printed on your own report, not this one. Laboratories differ, and yours is the one your doctor is reading.
What a high result can mean
By far the commonest cause of a mildly raised ALT is metabolic fatty liver disease. Alcohol, hepatitis B and C, medication (paracetamol, some antibiotics, statins early on, and many supplements), coeliac disease, thyroid disease and haemochromatosis all raise it too. Very high levels — many times the limit — point instead at acute injury: acute viral hepatitis, an overdose, or a period of poor blood flow to the liver.
What a low result can mean
A low ALT is not a recognised problem and is not usually investigated. It has been associated with frailty and with low vitamin B6 in older people, but on its own it is not a finding that calls for action.
What moves it
Weight and metabolic health above all, then alcohol in the days before the test, and strenuous exercise, which releases enzyme from muscle as well. Many prescription drugs and supplements move it. Because it drifts with weight, an ALT is best read against your own previous results rather than against the range alone.
What usually happens next
A mildly raised ALT is normally repeated after a few weeks rather than chased immediately, since many causes are transient. If it persists, the usual steps are an ultrasound, hepatitis B and C serology, ferritin and transferrin saturation, coeliac and autoimmune screens, a review of every medicine and supplement, and an honest conversation about alcohol.
Common questions
Does a raised ALT mean liver damage?
It means liver cells are leaking enzyme, which is a sign of irritation rather than of permanent damage. Many causes are reversible — weight, alcohol, a medication. What matters is whether it persists, how high it is, and what the rest of the panel shows.
Can exercise raise my ALT?
Yes, particularly heavy or unaccustomed exercise, because ALT is present in muscle too. AST usually rises more than ALT in that case. Avoiding hard training for a couple of days before a repeat test removes the question entirely.