Sabtu, 18 April 2009

Explanation of Viral Hepatitis Tests

IgM Antibody to hepatitis A
(Anti-HAV IgM or HAV IgM Ab)
Positive result defines a recent HAV infection.
May be negative in early infection (if collected within 5 to 7 days after onset of symptoms)
 Present for 3 to 6 months after onset of acute infection.
Total antibody to hepatitis A
(Anti-HAV Ab or HAV Ab)  Of extremely limited value in the diagnosis of acute infection.
 Positive result indicates past infection and immunity to HAV.
 Individuals given serum immune globulin for HAV prophylaxis may test as positive for at least six months.
Hepatitis B surface antigen
(HBsAg)  Used to diagnose an acute or chronic infection.
 First marker to appear in an acute infection.
 Disappearance indicates recovery from infection.
 Persistence for > 6 months indicates chronic infection (carrier).
 Individuals tested within 72 hours after administration of the vaccine may test as positive. (See anti-HBs, anti-HBc IgM and HBeAg.)
Antibody to hepatitis B surface antigen
(Anti-HBs or HBs Ab)  Only test which can be used to assess presence of protective immunity after immunization with hepatitis B vaccine.
 Levels of 10 MIU/mL (10 IU/L) are usually considered protective. Routine monitoring of levels in individuals who have received the complete course of vaccine is not considered necessary.
 Some individuals, e.g. healthcare workers, who are believed to have been exposed to the virus by a needlestick injury, should have their anti-HBs levels tested to determine whether they require administration of hepatitis B immune globulin (HBIG) and hepatitis B vaccine booster.
 Positive result in individuals with recent acute HBV infection indicates convalescence.
 Usually NOT detected when HBsAg is also present.
 In some cases of chronic hepatitis B infection, both HBsAg and anti-HBs can be detected. These antibodies are heterotypic and likely not protective.
 Antibody levels may decline with time.
IgM antibody to hepatitis B core antigen
(Anti-HBc IgM or HBc IgM Ab)  This test is expensive and should primarily be used if there is a high index of suspicion to indicate that the patient is in the early convalescence “window period” (2 to 16 weeks post infection) when HBsAg has disappeared and anti-HBs levels are not yet detectable.
 Positive result in patients who are also HBsAg positive usually indicates acute infection.
 Usually detectable for 3 to 12 months.
 Depending upon the threshold level of sensitivity, low levels may be detected in patients with chronic infection and reactivation.
Hepatitis B e antigen
(HBeAg)  Marker of active HBV replication.
 Also a marker of infectivity. However, the absence of HBeAg in a person who is HBsAg-positive does not imply that the individual is NOT infectious.
 Can be used to monitor therapy of patients with chronic HBV infection.
Antibody to hepatitis B e antigen
(Anti-HBe or HBe Ab)  Appears as HBeAg disappears.
 In chronic hepatitis B infection, a positive result indicates resolving or minimal liver disease.
 However, individuals who are HBsAg-positive and have anti-HBe present must still be considered infectious.
Total antibody to hepatitis B core antigen
(Anti-HBc or HBc Ab)  A positive result indicates past infection with hepatitis B virus.
 Usually persists for life.
 This antibody is absent in individuals who are immune solely as a result of vaccination.
 Up to 10% false-positive rate has been described in individuals with no documented infection to HBV. If uncertain, presence of one other marker, e.g., anti-HBs or anti-HBe would confirm previous exposure with HBV. Alternatively a negative repeat test later may indicate an earlier false-positive result.
Hepatitis B viral DNA
(HBV DNA)  Available by special request only. Of very limited value in the diagnosis of HBV infection.
 Used to determine the presence of HBV DNA circulating in the blood which is a measure of virus replication in the liver.
 Primary use is in monitoring treatment and clarifying some complex situations.
Antibody to hepatitis C
(Anti-HCV or HCV Ab)  Enzyme immunoassay (EIA) tests are the most common screening tests used to detect antibody.
 • With present EIA tests, a reactive result may be obtained after 8 to 12 weeks to several months following infection with HCV. Earlier generations of EIA tests often gave negative antibody results for up to 1 year.
 False-positive results are found in patients with autoimmune chronic active hepatitis, alcoholic liver disease and other disorders relating to hypergammaglobulinemia.
 Presence of antibody can be due to acute or chronic infection. It may represent only evidence of an infection with HCV.
 Persistently elevated ALT levels suggest chronic infection. Repeatedly normal levels do not exclude chronic infection, but suggest low grade inflammation.
 ALT values in some patients with HCV infection are within normal ranges.
Recombinant immunoblot for antibody to hepatitis C
(RIBA)  Supplementary test for the verification of EIA reactive results to HCV.
 Indeterminate results may be found in early seroconversion, immunosuppressed patients or those unable to mount a complete antibody response. Some of the conditions which give false-positives in the EIA may well give an indeterminate or non-specific result in the RIBA.
Polymerase chain reaction for hepatitis C
(PCR for HCV)  Available by special request only, as it is a research tool.
 Used to determine the presence of HCV RNA circulation in the blood which is a measure of virus replication in the liver.
 Can be used to assess the infectivity of the patient and monitor therapy.
 May be of use in early infection when antibody to the virus is undetectable, and in immunocompromised patients who may not seroconvert.
 Can be of use in resolving indeterminate RIBA results.
ALT
alanine aminotransferase  Liver enzyme test
 Used to assess extent of liver inflammation
 Can be used to monitor resolution of inflammation following acute or chronic infection

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