Saturday, June 15, 2013

Hepatitis B Virus: How to make interpretation lab diagnostic?


How do we determine if someone is infected with HBV? Three serologic tests are 
usually done to evaluate a person for HBV exposure: HBsAg, anti-HBc, and anti-HBs.

  • First, the HBsAg. The presence of HBsAg indicates infection with HBV.
  • Next, the anti-HBc. The anti-HBc is positive before the HBsAg becomes positive. In persons at risk for acute infection (known recent exposure or high liver enzyme level), the HBc immunoglobulin M (IgM) should be ordered as this may be the only serologic evidence of HBV exposure. In people with chronic HBV infection, the anti-HBc is predominantly immunoglobulin G (IgG), and the presence of anti-HBc confirmsan active or prior infection.
  • And, last, the anti-HBs. A positive anti-HBs indicates immunity from either exposure or vaccination.


If all markers of HBV including anti-HBs are negative, HBV vaccination should be offered.

HBV is transmitted during exposure to infected blood or body fluids via perinatal,
percutaneous, or sexual contact. A little-appreciated fact is that HBV can survive
for 7 days outside of the body, making dried blood and secretions a serious health threat.
In the areas of high HBV prevalence that I pointed out, most infected persons are exposed
at the timeof birth or in early childhood. The chance of developing a chronic infection after
exposure decreases with age: it is approximately 90% in infants, 30% in children younger
than 5 years of age, and less than 5% in adults. Thus, approximately 95% of adults
completelyrecover from an acute infection and do not become chronically infected.
The 5% who do notclear the virus are at risk to develop cirrhosis and liver cancer.
And the problem is that most are unaware of their infection. HBV is called a silent infection
 because most people -- children and adults -- do not have specific symptoms. Some have
 flulike symptoms, but they do not generally seek medical care, so the infection is undiagnosed.
In those who develop chronic infection, symptoms do not usually manifest until many years
later as a result of the sequelae of chronic liver disease.
VACCINATION
Vaccination is the most effective way to prevent HBV infection and its consequences.
The HBV vaccine is not only effective, but also its effects are durable. Immunization
protects the person who is vaccinated and prevents the transmission of infection to others.
 The CDC recommends vaccination for all infants and children younger than 19 years
as well as adults at increased risk for exposure and/or with chronic liver disease from other
 causes.
The HBV vaccine is administered as a 3-dose series. The third dose must be administered 
at least 8 weeks after the second dose and should follow the first dose by at least 16 weeks. 
The minimum interval between the first and second doses is 4 weeks. In infants,
 administration of the final dose is not recommended before age 24 weeks (164 days).
 The schedule is slightly different for people who are immune compromised, 
including those on hemodialysis.

Multiple manufacturers make the HBV vaccine and all brands are equivalent in
terms of immune response, so any brand can be given for any of the doses.
 Some formulations are also combined with the HAV vaccine or other vaccines.

The 3-dose HBV vaccine is effective in more than 90% of children and young
adults, but people who are immune compromised, including those older than 60
years of age, may have a less vigorous immune response to the vaccine.

Postvaccination serologic testing is not recommended for most patients.
Exceptions include children born to HBsAg-positive mothers, patients on hemodialysis,
and those at high risk for exposure to HBV. Routine booster doses are not recommended.
Although anti-HBs titers may drop to undetectable levels, immune memory protects
 those who have been vaccinated from infection.
The CDC recommends that the first dose of vaccine be given to a person at high risk for
 infection at the same visit as testing for HBV infection, unless an established
patient-provider relationship can ensure the patient will return for test results and that
vaccination can be initiated at that time if indicated.
This case is an excellent reminder that every patient encounter provides an opportunity
 to practice preventive care. HBV is one of the few diseases that can be prevented
with vaccination, thus decreasing the risk for end-stage liver disease and liver cancer.









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