Hepatitis B: How Serology Decides When Chronic Infection Is Treated

If you test positive for chronic hepatitis B, you may not be started on medication at all, and that surprises people who assume a virus in the blood always means a drug. The reason is that hepatitis B is staged before it is treated. A handful of lab values sort each person into a disease phase, and it is the phase, rather than the diagnosis itself, that tells your clinician whether the right move is a daily antiviral or a return appointment with more bloodwork. Two people can both carry the virus and leave the same clinic with opposite plans.

Key points#

• Chronic hepatitis B is diagnosed when the surface antigen (HBsAg) stays positive for more than six months.
• Four values do the staging: HBsAg, HBeAg, the liver enzyme ALT, and viral load (HBV DNA).
• The American Association for the Study of Liver Diseases (AASLD) treats the immune-active phase and cirrhosis, and generally monitors the immune-tolerant and inactive phases.
• Antiviral therapy suppresses the virus but rarely eliminates it, so treatment is usually long term and is reserved for where benefit is clear.
• Guidance updated in 2025 nudges more patients in the ambiguous middle toward treatment.

Step one: naming the situation with serology#

Before any number is weighed, the blood test has to say what kind of infection you have. The CDC's serologic panel separates states that can look alike at first glance.

• HBsAg (surface antigen) marks a current infection. When it persists past six months, the infection is chronic.
• Total anti-HBc reflects prior or ongoing infection and remains positive for life.
• IgM anti-HBc points to a recent, acute infection.
• Anti-HBs signals recovery or immunity from vaccination.

Put together, the pattern tells a story. Someone who is HBsAg negative, total anti-HBc positive, and anti-HBs positive has cleared a past infection. Someone HBsAg positive with a negative IgM anti-HBc has settled into chronic disease rather than an acute one.

A fifth marker, HBeAg, is a viral protein that broadly tracks with heavy replication. It does not by itself decide treatment. Instead, it changes the map: HBeAg-positive and HBeAg-negative disease are judged against different numeric cutoffs, so the same viral load can mean different things depending on whether HBeAg is present.

Step two: the phases and their thresholds#

AASLD reads two measurements against reference values. The ALT upper limit of normal it uses is 35 U/L for men and 25 U/L for women, lower than many older lab printouts show. Viral load is reported as HBV DNA in international units per milliliter (IU/mL).

Immune-tolerant phase. HBeAg positive, with a very high viral load (often in the millions or tens of millions IU/mL) but a normal ALT and little inflammation. The virus is abundant, yet the liver shows no active injury.

Immune-active phase. This is where treatment begins. AASLD defines it by two signals at once: an ALT at least twice the upper limit of normal (or clear injury on biopsy), together with HBV DNA above 20,000 IU/mL if HBeAg is positive, or above 2,000 IU/mL if HBeAg is negative. Both a replication signal and a tissue-injury signal must be present.

Inactive phase. HBeAg negative, anti-HBe positive, HBV DNA below 2,000 IU/mL, and a persistently normal ALT. Here the guidance recommends scheduled monitoring, because the liver is not under attack.

A useful way to picture it: viral load measures how loud the virus is, while ALT measures whether the liver is actually being hurt. Loudness alone does not warrant a drug; the guidance wants evidence of harm before committing you to years of therapy.

Why a positive test is not a prescription#

The first-line agents, PEG-interferon, entecavir, and tenofovir, suppress the virus effectively but rarely clear it. Treatment is therefore usually indefinite, and in the phases without active injury the expected benefit is modest while the commitment is real. So the guidance asks two questions together: is the virus replicating meaningfully, and is the liver being damaged. When both answers are yes, therapy lowers the risk of cirrhosis and liver cancer enough to justify long-term use. When only the viral load is high and ALT stays normal, as in the immune-tolerant state, the traditional approach favored watching.

Two circumstances override the phase table:

• Cirrhosis. If scarring is already present and HBV DNA is detectable, AASLD recommends antivirals regardless of ALT, because the liver has little reserve left to absorb further injury.
• Pregnancy. To reduce mother-to-child transmission, the guidance supports starting tenofovir in the third trimester when maternal HBV DNA is above 200,000 IU/mL. That threshold protects the newborn and is separate from the mother's own staging.

Where the line moved in 2025#

The framework keeps evolving. The 2025 AASLD/IDSA practice guideline, released in November 2025, broadened who should at least be offered treatment.

For immune-tolerant patients, it now conditionally suggests therapy for those over age 40, or with meaningful inflammation (grade 2 or higher) or fibrosis (F2 or greater) on biopsy or noninvasive testing. The reasoning is that a "tolerant" liver can accumulate slow damage over decades. AASLD labels the suggestion conditional and rates the underlying certainty of evidence as very low.

The update also addressed the indeterminate, or grey-zone, phase: patients who fit none of the classic boxes and who make up a large share of real clinics. Rather than defaulting to observation, the guideline supports shared decision-making, citing a systematic review in which antiviral treatment in this group was associated with a lower incidence of liver cancer. Quantitative HBsAg testing and noninvasive fibrosis assessment are folded in as extra tools that inform the same staging question. The direction is toward treating more of the ambiguous middle, while the core principle holds: serology and enzymes define the phase, and the phase, not the label of infection, sets the plan.