Clinical Laboratory - Microbiology


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Microbiologic Testing

Hepatitis Viruses

The significant hepatitis viruses include types A, B, C, D, and E. The transmission of B, C, and D is parenteral, close contact (e.g., sexually transmitted), or perinatal (congenital). Type A is spread by fecal/oral contamination and E is waterborne. The incubation periods are weeks long, somewhat shorter for A and E than the others.

Hepatitis A virus (HAV) infection is generally subclinical or a mild acute and self-limited infection, with clearance of the virus. A small number of HAV infections (<1%) lead to fulminant hepatitis.

Hepatitis B virus (HBV) infections are usually cleared by the host after acute infection, but in up to 20% of cases there is persistence of the virus. Most carriers of hepatitis B remain healthy, but up to 5% can develop ongoing hepatitis after 6 months, most often a chronic persistent hepatitis that eventually resolves, while in fewer cases chronic active hepatitis develops that can proceed to cirrhosis. The risk for hepatocellular carcinoma is increased when there is chronic hepatitis and cirrhosis.

Hepatitis C virus (HCV) produces a carrier state in over 80% of cases and some go on to chronic hepatitis. The risk for hepatocellular carcinoma is increased when there is chronic hepatitis and cirrhosis

Liver Function with Hepatitis Viruses

Non-specific laboratory findings with hepatitis include elevations in AST and ALT enzymes (the latter more specific for liver) and bilirubin (usually a mixture of direct and indirect). The greater the severity of liver disease, the higher the elevations. Liver biopsy may be useful in selected cases of chronic hepatitis to determine the severity of disease and to determine what therapy may be most efficacious.

Hepatitis A Virus (HAV) Serology

Diagnosis of acute HAV infection requires serologic evidence of HAV-IgM antibody. HAV-IgG antibody alone may just indicate past infection.

Hepatitis B Virus (HBV) Serology

Acute

Several serologic assays are available for HBV. The presence of HBsAg ('surface antigen') indicates acute disease. The presence of IgM HBcAb ('core antibody') indicates acute infection, and it appears before any other antibody. In months it is replaced by IgG antibody.

Chronic

HBsAg generally disappears by 6 months in persons who recover and clear the virus. Persistence of HBsAg correlates with a carrier state and, hepatitis is defined as 'chronic' if the HbSAg persists more than 6 months..

The presence of HBsAb ('surface antibody') indicates prior exposure to HBV with an immune response. Its presence is indicative that HBV vaccination was successful.

The presence of HBeAg ('e' antigen) occurs with acute infection and when it disappears and HBeAb ('e' antibody) appears, recovery is suggested. However, if HBeAg ('e' antigen) persists, then active chronic disease is likely.

The quantitation of HBV DNA by PCR is indicative of the amount of viral replication and may be used to monitor antiviral therapy.

Hepatitis C Virus (HCV) Serology

Both acute and chronic HCV infection can be diagnosed by detection of antibody to HCV, but the antibody does not confer immunity. Anti-HCV is not present in all cases of HCV, and some positive tests are false positives. Thus, more sensitive and specific tests detect HCV RNA by PCR or branched DNA assays.

Genotyping of HCV RNA is available to determine possible severity of disease and select treatment strategies.


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