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Hepatitis Surveillance

Use of Serologic Tests for Diagnosis

Issued April, 1996

Serologic testing for the diagnosis of hepatitis, beginning with hepatitis B surface antigen (HBsAg) in 1972, immunoglobulin-M antibody to hepatitis A virus (IgM anti-HAV) in 1981, and IgM antibody to hepatitis B core antigen (IgM anti-HBc) in 1984, has been critical in distinguishing the types of viral hepatitis. Serologic testing for any marker using one or more tests has increased from 60% in 1983 to 94% in 1993 (Figure 1). By 1993, only 6% of reported cases were diagnosed on the basis of the HBsAg test alone. However, there has been a decline in the number of cases reported in which testing for both hepatitis A and hepatitis B was done. In 1989, 76% of physicians reported using tests for both types (the highest percentage reached); this declined to 70% in 1990, 68% in 1991, 63% in 1992, and to 55% in 1993. At the same time, the number of cases reported in which testing only for hepatitis A was done increased over this period, from 15% in 1989 to 28% in 1993. The reliance on testing for hepatitis A alone for these cases may be related to the higher incidence of hepatitis A in community-wide outbreaks since 1989.


Case Definition

Epidemiologic data about reported cases of acute viral hepatitis are essential for defining the groups at risk and for monitoring changes in such groups. Since new disease acquisition is the event of interest, chronic infections should not be reported.

In 1990 the VHSP updated the case definition for acute viral hepatitis to include IgM anti-HBc for improved diagnosis of acute hepatitis B, to clarify the reporting of NANB hepatitis, and to include delta hepatitis as a separate diagnostic category. The clinical criteria remain the same: an acute case must include an illness with discrete date of onset, and jaundice or elevated serum aminotransferase levels greater than 2.5 times the upper limit of normal. The serologic criteria used to distinguish the different types of hepatitis were as follows: hepatitis A is defined as IgM anti-HAV-positive (regardless of HBsAg status); hepatitis B as IgM anti-HBc-positive (if done) or HBsAg-positive and IgM anti-HAV-negative (if done); and NANB hepatitis as IgM anti-HAV-negative, and IgM anti-HBc-negative (if done) or HBsAg-negative. Although by 1993 only 55% of reported cases were tested for both hepatitis A and B, 87% had sufficient serologic testing to designate a specific type. Only those patients with a specific serologic diagnosis are included in the following analyses.

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Cases are excluded if they do not satisfy the criteria for acute viral hepatitis. Among serologically confirmed cases in 1993, 6% of hepatitis A cases, 13% of hepatitis B cases, and 9% of NANB hepatitis cases were excluded because they failed to meet the case criteria. Compared with hepatitis B patients who fulfilled the criteria for acute hepatitis, more persons with hepatitis B who were asymptomatic or had no date of onset were <14 years of age, were Asian/Pacific Islander, were dialysis patients, or had histories of blood transfusions or surgery.

Except for age, NANB hepatitis patients not meeting the case definition showed a similar pattern. Compared with NANB hepatitis patients who fulfilled the criteria for acute hepatitis, more persons with NANB hepatitis who were asymptomatic or had no date of onset were >40 years of age, were patients undergoing dialysis, or had histories of surgery. This pattern, as well as that for hepatitis B, is consistent with that for the earlier years. For both hepatitis B and NANB hepatitis, these findings suggest that these persons may have been routinely screened for HBsAg or for antibody to the hepatitis C virus (anti-HCV), and found to be positive without any evidence of acute illness.

Hepatitis A and B coinfections were examined in the 1993 data, and constituted approximately 1% of cases meeting the case definition. These cases displayed no specific clustering or associations with geographic or demographic factors. For purposes of risk factor analysis, these cases were counted twice, and included as hepatitis A cases and hepatitis B cases.





  
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This article was provided by U.S. Centers for Disease Control and Prevention. Visit the CDC's website to find out more about their activities, publications and services.
 

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