What do ALT, AST and HBV DNA actually mean?

If you live with chronic hepatitis B, three results tend to follow you from one blood test to the next: ALT, AST and HBV DNA. They measure different things, and they are most useful read together rather than one at a time.

This article explains what each number represents. It does not tell you what your own results mean — that conversation belongs with your doctor, who is reading them alongside your history, scans and everything else.

ALT — a marker of liver cell inflammation

Alanine aminotransferase is an enzyme found mostly inside liver cells. When those cells are inflamed or damaged, ALT leaks into the bloodstream, so a raised ALT is a general signal that something is irritating the liver.

Two things are worth knowing:

• "Normal" is not one universal number. Reference ranges differ between laboratories, and the healthy upper limit is generally lower for women than for men. Always read your result against the range printed on your own report.
• ALT is not specific to hepatitis B. Alcohol, fatty liver, some medications and supplements, and recent strenuous exercise can all raise it. A single high reading is a prompt to look further, not a diagnosis.

AST — related, but less liver-specific

Aspartate aminotransferase does a similar job to ALT, but it is also present in heart and skeletal muscle. That makes it less specific to the liver on its own, which is why it is usually interpreted next to ALT rather than in isolation. Clinicians sometimes look at the relationship between the two values, along with other markers, when building a picture of liver health over time.

HBV DNA — how much virus is circulating

HBV DNA measures the amount of hepatitis B virus genetic material in your blood, usually reported in international units per millilitre (IU/mL). Where ALT and AST describe how the liver is reacting, HBV DNA describes how active the virus itself is.

Because the range spans several orders of magnitude, results are often written in scientific notation — and a change that looks dramatic on paper may or may not be clinically meaningful. Interpretation depends on your treatment status, your other markers, and how the number has moved across previous tests.

Why they are read together

No single one of these values settles anything on its own. A person can have a high viral load with normal ALT, or a raised ALT driven by something entirely unrelated to hepatitis B. Clinicians look at the combination, the direction of travel over months and years, and other information such as HBeAg status, imaging or elastography.

This is also why keeping your own history matters. A single result is a dot; a run of results is a line, and the line is what your doctor is actually reading.

What to do with your results

• Read each value against the reference range on your own report, not against numbers quoted online.
• Bring your history to appointments, not just the latest result.
• Ask your clinician what they are watching in your particular case, and how often they want you retested.
• Do not start, stop or change any medication based on a lab result alone.

Further reading

• World Health Organization — Hepatitis B fact sheet
• Hepatitis B Foundation
• ASHM — Australasian Society for HIV, Viral Hepatitis and Sexual Health Medicine