SAN FRANCISCO – Tests for hepatitis B surface antigen, surface antibody, core antibody, and type “e” antigen each play an important role in diagnosing infection and level of infectivity, Dr. Tina Q. Tan said at the annual meeting of the American Academy of Pediatrics.
These serologic markers of the hepatitis B virus help distinguish infection with this virus from other hepatitis virus infections, all of which cause nonspecific signs, symptoms, and laboratory findings, said Dr. Tan of Northwestern University, Chicago.
Hepatitis B prodrome can cause fever; malaise; headache; myalgia; nausea or vomiting; and right upper-quadrant pain. Jaundice or hepatomegaly may be seen, but more than 50% of infections are asymptomatic.
A positive hepatitis B surface antigen (HBsAg) test almost always indicates that the patient is either acutely or chronically infected, she said. Very rare cases have been false positives. A positive hepatitis B surface antibody (HBsAb) test indicates that the patient is immune to the hepatitis B virus or to infection with the virus, either because of vaccination or because the patient gained immunity by recovering from an acute infection.
A positive hepatitis B core antibody (HBcAb) test means different things, depending on the type of antibody. A patient who is IgM positive has recently been infected with the hepatitis B virus. Positivity to IgG antibody could indicate a past infection or a chronic infection with hepatitis B virus. In rare cases, patients who have been vaccinated against hepatitis B will have false-positive HBcAb IgG results.
Knowing what each of these tests represents leads to a relatively simple three-step process for initial interpretation of the hepatitis B panel of tests, Dr. Tan suggested:
1. If the HBsAg is negative and the HBsAb is positive, then the patient is immune to hepatitis B, either through natural infection or through vaccination.
2. If the HBsAg is positive and the HBsAb is negative, then the patient has either acute or chronic hepatitis B infection.
3. If both the HBsAg and HBsAb are negative and the HBcAb is positive, this could be a false-positive result, or the patient is either chronically infected or recovering from acute infection, or the patient may be immune to hepatitis B but the HBsAb level is too low to be detected, Dr. Tan said.
A fourth serologic test, for hepatitis B “e” antigen (HBeAg), is a marker of infectiousness. People with HBeAg have very high concentrations of hepatitis B viral DNA in their bodies and are at very high risk of transmitting the infection to others.
These serologic marker tests may need to be repeated over time to serially assess the patient's status, she said. A chronic carrier of active hepatitis B who is HBeAg positive, for example, should be followed with HBeAg tests until a negative result suggests that the level of infectiousness has dropped.
Patients who are being followed or treated for acute hepatitis B infection should get repeated marker tests to look for hepatitis B surface antigens to appear, which would indicate that they've recovered from the infection. If HBsAg tests remain negative for more than 6 months, the patient is a chronic carrier of the virus. “This is what you're trying to prevent,” she said.
An estimated 78,000 new hepatitis B infections are diagnosed each year in the United States. Approximately 5,000 people each year die prematurely from chronic liver disease caused by chronic hepatitis B infection.
The childhood risk for an acute infection to become a chronic infection falls from a high of about 95% of babies who are infected at birth to about 10% of children who are infected with hepatitis B at age 5 years.
The risk for perinatal transmission of hepatitis B infection ranges from about 20% if the mother is HBsAg positive to as much as 90% if the mother also is HBeAg positive.
Use of hepatitis B vaccine and hepatitis B immune globulin can prevent perinatal transmission in about 95% of cases.
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