Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1372 page)

   Presence of HBeAg implies infective HBV present in the serum, but its absence on conversion to HBeAb does not rule out infectivity, especially in persons infected with genotypes other than A.

   During the HBeAg-positive state, usually 3–6 weeks, hepatitis B patients are at increased risk of transmitting the virus to their contacts, including babies born during this period. Exposure to serum or body fluid positive for HBeAg and HBsAg is associated with three to five times greater risk of infectivity than when HBsAg positivity occurs alone.

   HBeAg may be negative in the “precore mutant” form of hepatitis B and can be highly infectious. HBeAg-negative strains respond similarly to antiviral treatment.

   Measurement of HBV DNA is now recommended, especially in persons with increased ALT but negative HBeAg.

HEPATITIS C VIRUS (HCV) ANTIBODY

   Definition

   HCV is now known to be the causative agent for most, if not all, blood-borne non-A, non-B hepatitis. The presence of anti-HCV indicates that an individual may have been infected with HCV and may be capable of transmitting HCV infection. Also known as HCV antibody, non-A, non-B hepatitis.

   
Normal range:
Negative.

   Use

   Screening for past (resolved) or chronic hepatitis C.

   Interpretation

Increased In

   Hepatitis C infection: Current and past exposure.

   Limitations

   Presence of HCV antibodies in serum does not imply protective immunity. False-positive anti-HCV results are rare in certain clinical settings, because the majority of persons being tested have evidence of liver disease, and the sensitivity and specificity of the screening assays are high. However, among populations with a low prevalence of HCV infection, false-positive results do occur. This is of concern when testing is performed on asymptomatic persons for whom no clinical information is available, when persons are being tested for HCV infection for the first time, and when testing is being used to determine the need for postexposure follow-up.