HBeAg is the “soluble” or extractable part of the “core” antigen of the hepatitis B virus (HBV). The presence of HBeAg indicates that the virus is actively multiplying and is highly contagious. HBeAg appears in the blood shortly after HBsAg. It stays in the blood for about 3 to 6 weeks after the acute (symptomatic) phase of the disease and may persist for a long time or reappear in the case of active chronic hepatitis. Therefore, the HBeAg test is most often used to indicate the level of contagiousness. It is also useful in monitoring the efficacy of a treatment. A positive (reactive) HBeAg result combined with a negative (non-reactive) anti-HBe result confirms a high degree of contagiousness. When the anti-HBe is also reactive, this means the individual is in the process of healing and is less contagious.
A non-reactive HBeAg result (with a reactive anti-HBe result) in a person with hepatitis B indicates that the infection is in its initial phase, before peak replication of the virus. If the anti-HBe is reactive, it may indicate that viral replication is now very low. There are subtypes of HBV that do not produce HBe. These subtypes are usually found in Asia, the Middle East and increasingly in Europe.