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Prevention of post-transfusion viral hepatitis B

You are here : Home/ Blood Bank Zone/ Trasfusion Transmitted Diseases/ 4. Prevention of post-transfusion viral hepatitis B

4. Prevention of post-transfusion viral hepatitis B

Most blood transfusion services have established routine screening of donated blood units for HBsAg (HBV) for many years. The introduction of third generation sensitive tests has greatly reduced the incidence of post-transfusion hepatitis B but the risk has not been eliminated. The minimum level of detection of 1-IBsAg by the 3rd generation assay system is more than 100 minimum infective doses of I-IBV. In addition, the risk of infection is higher in pooled plasma products. The risk of transmission of HBV can further be reduced by screening the blood donations for anti HBc, as it is only market of HBV during the window period.

Besides screening of all blood and blood components, Active HBV vaccination is another approach to reduce the rate of transmission of HBV.

Non-A Non-B Hepatitis (Hepatitis C infection)

NANB hepatitis was initially the name given to viral hepatitis where no specific viral agents had been identified. The epidemiology and mode of tranmission of NANB are similar to those of I-IBV. There are three types of NANBH recognized

1. Post-transfusion or parenteral
2. Enteric
3. Sporadic community-acquired

Parenterally transmitted NANB hepatitis is the most common cause of post-transfusion hepatitis and is caused by a single stranded RNA virus with a genome of approximately 10,000 nucleotides and is 50-60 nm in diameter as Hepatitis C virus. It has recently has shown that in most cases of non-A non B post-transfusion hepatitis, there is serological evidence of infection with hepatitis C virus, but existance of other agents capable of causing a small proportion of NANB cannot be excluded.

In countries where all donations are routinely screened for HBsAg, most cases of post-transfusion hepatitis are caused by one or emore viral agents i.e. non-A Non-B hepatitis viruses. Until recently, the diagnosis of non-A non-B post-transfusion hepatitis was based on the exclusion of all known hepatotrophic viral agents (I-IBV,CMV,EBV,etc). and non-viral causes.

Surrogate tests have been widely used to identify donors at risk for transmission of NANBH. These are serum alanine aminatransferase (ALT) and antibodies to hepatitis B core antigen (anti-HBc).

Introduction of testing for serum ALT levels may reveal subclinical infection in donors, however increased activity of this enzyme is not specific to NANBH carriers. Correlation of anti-HBc as a surrogate market for NANBH may not be appropriate in HBV endemic areas.

Test for Hepatitis C virus

The development of anti-HCV assay have reduced or supplemented the need for surrogate markets testing. The prevalance of anti-HCV in patients with chronic non-A nan-B PTH is 60-80%.

Two generations of ELISA test system have been developed for detection of anti-HCV. First generation assays detect antibody to non-structural antigen C100-3. Antibody to this antigen is usually detected 10-15 weeks after exposure.

Second generation assays have now been developed which are more sensitive than the first generation assays and detect antibodies to both structural and non-structural HCV antigens. These tests increase the proportion of detection of HCV cases and shorten the window period.

Supplemental tests - Neutralization assay and Recombinant immunoblot assays (RIBA) have been developed which correlate well with 2nd generation EL1SA system.

Prevention of PT NANBH/Hepatitis C viral infection

It is very important to follow the recipients and identify the of donors involved in post-transfusion on hepatitis. Besides effective donor screening and a detailed medical history, the following tests may also be done to reduce the incidence of PT NANBH.

1. ALT levels
2. Anti-HBc Non-specific �Surrogate� market
3. Anti-HCV screening

In most of the western countries, screening of all donated blood units for anti-HCV has become mandatory since 1991, however, it is not mandatory in India because of two reasons:

1. High cost of available anti-HCV test kits.
2. Absence of any data in India to confirm whether the available test system is applicable to Indian situation or whether the variants of I-ICY in India are same as those in other countries.
However, each blood transfusion centre may take its own decision for screening of anti-HCV.

Hepatitis Delta virus Infection (HDV)

Hepatitis D infection can occur after parenteral exposure and is caused by a defective RNA (HDV) virus that requires HBV as a �helper� virus. The Delta virus has a low molecular weight and is coated by HBsAg. Superinfection of carrier of HBsAg with HDV is associated with achronic course of the delta infection and an increase in incidence of chronic hepatitis. HDV can be transmitted by blood, fresh blood components and by coagulation factor concentrates.

Screening for HBsAg in blood donors minimizes but does not abolish the risk of post-transfusion delta hepatitis in transfusion recipients with previous HBV infection.

Hepatitis A viral infection

HAV infection is reported to cause PTH only when the blood is collected during the stage of viraemia. As n� chronic carrier stage exists for HAY, it is unnecessary to screen donors for HAY and the possibility of Hepatitis A in blood transfusion is significantly low.

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