Acute Hepatitis: Hepatitis that persists for less than six months. There may be no symptoms, or symptoms such as fatigue, nausea, and jaundice may occur.

Active Hepatitis: Inflammation of the liver. In the case of chronic hepatitis B infection, it is due to an incomplete immune response against the virus that results in damage to individual liver cells.

Adverse Events: Undesirable experiences occurring during medical therapy or after immunization that may or may not be related to the medication or vaccine.

Alanine Aminotransferase (ALT): An enzyme found in the blood. Primarily produced by injured hepatocytes and is a marker of inflammation. Therefore, elevated levels of ALT usually indicate liver cell damage or necrosis (cell death).

Antigens: Foreign substances (e.g., bacteria or viruses) in the body that are capable of inducing an immune response, usually the production of antibodies.

Antiviral: Any medicine capable of destroying a virus or lowering its ability to multiply.

Carrier: A person that has a specific infectious agent and is a potential source of infection. Hepatitis B carriers may never become sick but are able to infect others with the virus.

Chronic Hepatitis: The presence of hepatitis B virus in blood for longer than six months.

Cirrhosis: Liver disease characterized by diffuse scarring and abnormal liver tissue.

Clinical Trial: A study of how a drug will work in humans. Clinical trials usually involve many people and compare various end points such as safety and efficacy of a drug with a placebo or with other approved treatments.

Compensated Liver Disease: The liver continues to function, although it is damaged. This condition can lead to decompensated liver disease, which results in decreased liver function.

Dose: The specified quantity of a medication to be given at one time.

Enzyme: A protein capable of producing certain chemical changes.

HBV DNA: Genetic information of the hepatitis B virus (HBV). It indicates concentration of HBV in blood (viral load) and ongoing viral replication.

Hepatic Decompensation: Failure of the liver to repair itself from injury, resulting in a decrease in liver functions.

Hepatitis B: Liver disease caused by the hepatitis B virus (HBV). HBV is found in the blood of infected persons and is commonly transmitted through unprotected sex.

Hepatitis B Core Ag (HBcAg): A core protein antigen of the hepatitis B virus not readily detectable in serum. It is an indicator of replicating hepatitis B virus.

Hepatitis B Core Antibody (anti-HBc): Antibody to the hepatitis core antigen. Appears at the onset of symptoms in acute hepatitis B and persists for life. The presence of anti-HBc indicates previous or ongoing infection with HBV.

Hepatitis B e Ab (anti-HBe): Antibody to HBeAg that indicates good probability of long lasting viral clearance.

Hepatitis B e Antigen (HBeAg): Secreted product of the nucleocapsid gene of HBV found in serum during acute and chronic hepatitis B. Its presence indicates the virus is replicating and the infected individual is potentially infectious.

Hepatitis B Immune Globulin (HBIG): A product available for prophylaxis against hepatitis B virus infection. HBIG is prepared from plasma containing high titers of anti-HBs and provides short-term protection (three to six months).

Hepatitis B Surface Antibody (anti-HBs): The presence of anti-HBs is generally interpreted as indicating recovery and immunity from HBV infection.

Hepatitis B Surface Antigen (HBsAg): A serologic marker on the surface of HBV. It can be detected in high levels in serum during acute or chronic hepatitis.

Hepatocellular Carcinoma (HCC): A primary cancer of the liver which can result from chronic hepatitis B infection.

Histology: Study of structure and composition of tissue as examined under a microscope. It is the only reliable way to assess extent of scarring and the most precise way to diagnose liver damage.

Liver Inflammation: A response due to injury or destruction of tissues in the liver.

Nucleoside Analogue: A chemical compound structurally similar to the building blocks of DNA and RNA.

Perinatal (Vertical) Transmission: Passage of a disease-causing agent (a pathogen) vertically from mother directly to baby during the perinatal period, the period immediately before and after birth. Transmission might occur across the placenta or in the breast milk.

Prescribing Information: The manufacturer's information about the medication for prescribers. Also referred to as a package insert, product label, or product information.

Placebo: An inactive substance or preparation that looks like real medicine. It is sometimes called a sugar pill.

Resistance: Refers to the ability of an organism, such as a virus, to become less sensitive to a drug that is generally used to treat the organism. In some cases this is the result of viral mutation.

Seroconversion: The development of an antibody in the serum in response to an antigen.

Side Effect: See Adverse Events.

Sustained Response: A response that persists even after drug therapy is stopped; equated with long-term successful therapy. Usually a time frame is specified, but if not, most sustained responses are measured six to 12 months after therapy.

Virus: A tiny organism that multiples within cells and causes disease such as chickenpox, measles, mumps, rubella, and hepatitis. Viruses are not affected by antibiotics, the drugs used to kill bacteria.

Viral Replication: The process by which a virus multiplies to make copies of itself after entering a living host cell.

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