Adequacy and safety of blood is the prime concern of medical community and the society at large. It is documented that voluntary donors are the safest group as the positivity for infections transmitted through blood transfusions are very less. World Blood Donors day (14th June every year) and National Blood Donation day (1st Oct) are celebrated to promote voluntary donation in the country.
Transfusion Transmitted Infections (TTI)
Stringent donor selection criteria and adoption of improved sophisticated and sensitive testing methods have reduced the risk of TTI, but these could not be eliminated fully. The greatest threat to the safety of the blood supply is the blood donation by sero-negative donors during the infectious window period. Many bacteria, viruses and parasites can be transmitted through blood if a person is infected with these organisms. Majority of the organisms after the entry in to the human blood show signs and symptoms of the illness. But there are a few organisms that can harbour in human blood without showing any signs and symptoms for a long period. This condition is called ‘chronic carrier state’. Human Immunodeficiency viruses, Hepatitis B virus, Hepatitis C virus, Treponema Pallidum, bacteria causing syphilis, Plasmodium that causes malaria are the major ones among these.
These can be transmitted and cause serious complications in the recipient of the infected blood. After blood donation, each blood unit will be tested and only test-negative blood will be transfused to patients. Tests for these five organisms are mandatory in our country. In many countries more infective organisms are screened like West Nile Virus (WNV), Cytomegalovirus (CMV), Human T-Cell Lymphotrophic Viruses (HTLVs), Parvovirus B19 etc. Any organism after entry to the blood stream will multiply in number. Human body starts producing antibodies against these organisms to eliminate it.
Tests are designed to find out the presence of markers of infection in the blood. Enzyme linked Immuno Sorbent Assay (ELISA) is the test method currently used by most of the blood banks. The antigens, antibodies and the nucleic acid (genetic material) are the markers of infection. Tests to detect the antigen, antibody or antigen-antibody combinations are available. The ability to detect depends on the amount of antigen/ antibody present in the blood.
The window period
Responses of the person to the infective organism also vary. Some people respond poorly to the infection and take more time to produce the antibodies, thus delay detection. Usually, it takes weeks or months to produce antibodies. But the blood from this person can be infectious and get transmitted to the recipient of the blood. This period is called the window period. An earlier marker is nucleic acid , either DNA or RNA, specific for each organism.
To reduce the window period, tests are available to detect the DNA/RNA called Nucleic Acid Amplification Test (NAT) even before the production of antibodies. This test is an addition to the previous tests. This test is more sensitive but cost is the limiting factor for implementation in all blood banks. Blood tested with this test is also not 100% safe as it too require a minimum number of organisms to be detected. Over the last two decades, much attention has been given to the prevention of Transfusion Transmitted Infections. Even after all these measures 100% safety could not be ensured.
Blood safety starts from the donor. A safe donor is the key to safe blood. So it is the prime responsibility of the donor to be safe. Repeat voluntary blood donation is the corner stone in blood safety. Statistics from NACO shows that positivity rates for viral infections like Human Immunodeficiency Virus 1&2, Hepatitis B &C and syphilis are less among voluntary Non Remunerated blood donors compared to the replacement family donors. Annually India requires 8 million units of blood, but only 5 million units are collected. Sixty-two out of 193 WHO member states report collecting 100% of their blood supplies from voluntary donors, including countries like Zimbabwe. Some countries have high levels of voluntary blood donors. Switzerland have 113/1,000, Japan 70/1,000 while India has only 4/1,000 people. It is recommended that 1-3% of a country’s population should donate to meet the blood requirement. It is the responsibility of the civil society to achieve this goal.
(The writer is head of Department, Transfusion Medicine, Sree Chitra Tirunal Institute for Medical Sciences & Technology, Thiruvananthapuram)
