<How is it possible for only this part of the hepatitis related tests
to
<be positive when the person, in this case my daughter, was vaccinated
<against hep b as a child?  This came up in the blood tests they do
when
<donating blood.  Could this be a false positive twice?  Any info would

<be appreciated.

"Anti-HBc appears at the onset of symptoms or liver test abnormalities
in acute HBV infection and persists for life. Acute or recently
acquired infection can be distinguished by the presence of the IgM
class of anti-HBc, which is detected at the onset of acute hepatitis B
and persists for up to 6 months if the disease resolves. In patients
who develop chronic hepatitis B, IgM anti-HBc can persist at low levels
during viral replication and can result in positive tests for IgM
anti-HBc (40). In addition, false-positive IgM anti-HBc test results
can occur. Because the positive predictive value is low in asymptomatic
persons, for diagnosis of acute hepatitis B, testing for IgM anti-HBc
should be limited to persons with clinical evidence of acute hepatitis
or an epidemiologic link to a case.

In persons who recover from HBV infection, HBsAg is eliminated from the
blood, usually within 3--4 months, and anti-HBs develops during
convalescence. The presence of anti-HBs typically indicates immunity
from HBV infection. Infection or immunization with one genotype of HBV
confers immunity to all genotypes. In addition, anti-HBs can be
detected for several months after hepatitis B immune globulin (HBIG)
administration. The majority of persons who recover from natural
infection will be positive for both anti-HBs and anti-HBc, whereas
persons who respond to hepatitis B vaccine have only anti-HBs. In
persons who become chronically infected, HBsAg and anti-HBc persist,
typically for life. HBsAg will become undetectable in approximately
0.5%--2% of chronically infected persons yearly, and anti-HBs will
occur in the majority of these persons (41--44).

In certain persons, the only HBV serologic marker detected in serum is
anti-HBc. Isolated anti-HBc can occur after HBV infection among persons
who have recovered but whose anti-HBs levels have waned or among
persons in whom anti-HBs failed to occur. Persons in the latter
category include those with circulating HBsAg levels not detectable by
commercial assays. These persons are unlikely to be infectious except
under circumstances in which they are the source for direct
percutaneous exposure of susceptible recipients to substantial
quantities of virus (e.g., through blood transfusion or following liver
transplantation) (45). HBV DNA has been detected in the blood of <5% of
persons with isolated anti-HBc (46). Typically, the frequency of
isolated anti-HBc relates directly to the prevalence of HBV infection
in the population. In populations with a high prevalence of HBV
infection, isolated anti-HBc likely indicates previous infection, with
loss of anti-HBs. For persons in populations with a low prevalence of
HBV infection, an isolated anti-HBc result often represents a
false-positive reaction. The majority of these persons have a primary
anti-HBs response after a 3-dose series of hepatitis B vaccine (47,48).
Infants who are born to HBsAg-positive mothers and who do not become
infected might have detectable anti-HBc for <24 months after birth from
passively transferred maternal antibody. "

http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5416a1.htm

As you can see from the above recommendations that post vaccine testing
to check for the seroprotective response to the vaccine is not
mandatory. The rate is usually greater than 95% but not 100%. The
vaccine does not work in some people.

You can have a false positive Anti-HBc depending on tests used. A
rechallenge with vaccine would yield the presence of anti-HBs that
declined with time. This would indicate past infection with resolution
of hepatitis with the generation of anti-HBs. Vaccination does not
induce anti-HBc antibodies.

"Isolated anti-HBc positive HCWs should be tested for anti-HBc IgM and
HBV-DNA: if negative, anti-HBs response to vaccination can distinguish
between infection (anti-HBs &gt;50 mUI/ml 30 days after 1st
vaccination: anamnestic response) and false positive results(anti-HBs
&gt;10 mUI/ml 30 days after 3rd vaccination: primary response); true
positive subjects have resistance to re-infection. and do not need
vaccination."

Euro Surveill. 2005 Oct 1;10(10) [Epub ahead of print]

European recommendations for the management of healthcare workers
occupationally exposed to hepatitis B virus and hepatitis C virus.

PMID: 16282641 [PubMed - as supplied by publisher

As far as the false positive twice statement, it is test methodology
dependent. If it is the same manufacturer being used then it is the
same test no matter how many times it is done. Having it done with an
alternate method manufacturer is better than simply repeating it. These
are immunoassays and cross-reactivity is from the manufacturer's system
can be country wide.
With borderline results, I respin the blood sample to clear it of some
interference and repeat the test and if still positive then it is
reported as positive.