Hepatitis B-Diagnostik bei Blutspendern: Verfahren und Interpretation auffälliger Befundkonstellationen. Diagnosis of hepatitis B in blood donors: procedure and interpretation of suspicious results

Abstract

Abstract Several test systems are available for the diagnosis of infection with the hepatitis B virus (HBV). In most cases, reliable results lead to the detection of acute infection or chronic HBV infection or immunity due to past infection or active immunization. In some cases, however, results may be difficult to interpret or even misleading and special assays are necessary to answer more specific questions. During acute or chronic HBV infection, not only the qualitative detection of HBsAg is necessary, but also the quantitative determination may allow for the diagnosis of activity of the disease. In most cases, HBeAg closely correlates to viraemia and infectivity, but mutations within the pre-core region of the HBV genome may lead to a loss of HBeAg and to seroconversion to anti-HBe while the virus concentration in serum is high and patients are severely ill. Anti-HBc assays often give false positive test results which can be ruled out by re-testing a serum dilution. IgM antibodies against HBcAg are not only found during acute infection but may become positive again during reactivation in chronic virus carriers. Different genotypes of the virus are prevalent in different parts of the world and multiple infections are possible; these may lead to the simultaneous detection of HBsAg and anti-HBs. Viral DNA can be detected by several methods with different lower detection limits. Screening of blood donors to rule out HBsAg-negative virus carriers is done by polymerase chain reaction, since this method has the highest sensitivity. Infectivity of HBsAg-positive carriers may also be determined by other assays such as branched DNA or molecular hybridization. Patients on treatment with nucleoside analogs may show an increase in DNA concentration after an initial decrease or even loss. This may be due to mutation within the YMDD-motif of the DNA polymerase which can be detected by sequence analysis. In this overview, hints will be given on how to evaluate positive results in the different assays. In addition, it gives advice on how to establish a suitable diagnosis for a variety of clinical questions. Several suspicious constellations are discussed as well as the possibilities to clarify them.