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Nucleic Acid Amplification Testing

While NAT is widely used in most countries, the adoption of this technology in India is abysmally low!

India has a fragmented blood banking system with about 3000 blood banks across the country. India has also one of the highest numbers of transfusion transmitted infections (TTI) in the world. When the donated blood units in a blood bank is not screened with the most sensitive tests for the presence of viruses like HIV, hepatitis B, and hepatitis C, then there is a higher risk of passing an infection through the blood that is transfused.

NAT is an advanced molecular technique that is more sensitive than the conventional serology (ELISA/Chemi) based tests. Unlike serology, NAT does not wait for the body’s immune response but directly detects the nucleic acid of the virus. Due to this, NAT detects early stage infections as well as Occult Hepatitis B infections that may be missed by the conventional serological methods. There are two technologies used in NAT screening namely Transcription Mediated Amplification (TMA) and PCR. While both are acceptable and similar technologies, TMA seems to be more optimized for detecting lower concentration of viruses and high throughput situations with quick turnaround times. The TMA process is isothermal and the entire process is performed in a single tube.

Screening Methodologies

NAT is performed in two methods, i.e., Individual Donor NAT (ID-NAT) or Mini-Pool NAT (MP-NAT).

ID-NAT.  In ID-NAT, each donor sample is tested individually. As emphasized by Dr Dhinesh Kumar, Senior Specialist, Transfusion Medicine, Aster Medcity “ID-NAT is a direct and effective way of testing; which is proven to be more sensitive in identifying the infected units. Using ID-NAT, we ensure that every blood unit which gets transfused is made as safe as possible.” Individual donor testing offers highest screening sensitivity of the assay. In our country, where the prevalence of HIV, HBC, and HCV among the blood donors are higher, and several cases of TTI have been reported from various parts of the country, it is imperative that each donor blood is tested individually without any compromise. Globally too, there is a shift from pooled testing towards individual testing. Recent examples include Japan, Korea, Saudi Arabia, UAE, and Switzerland.

MP-NAT. In MP–NAT, samples of six or more different donors are mixed (grouped) together and that mixed specimen is tested. If the result comes negative, one has to assume that all the six blood units that were part of that sample mixture are negative for any viruses. Pooled NAT testing can compromise the results due to viral load dilution and resultant reduction in screening sensitivity. However, it may be a cheaper option for blood banks those who are looking for incremental risk reduction than absolute risk reduction.

NAT Adoption in India

The first blood bank in country to adopt NAT is Indraprastha Apollo Hospital, New Delhi who evaluated and implemented NAT in their routine screening in 2006. Karnataka State Government was the first in India to make ID-NAT mandatory in all government supported blood banks in 2012. Orissa State Government has adopted NAT for their government supported blood banks. Currently about 100 blood banks including AIIMS, New Delhi; PGI, Chandigarh; CMC, Vellore; Hinduja Hospital, Mumbai; Medanta Medicity, Gurgaon; Narayana Hrudayalaya, Bangalore are currently using NAT in ID-NAT format and about 40 blood banks are using MP-NAT.

While NAT is widely used in most countries, the adoption of this technology in India is abysmally low! Only about 140 out of the 3000 blood banks have adopted NAT screening and only about 10 percent of blood that is issued in the country is NAT tested. Time and again we come across reports of innocent patients getting infected with HIV or Hepatitis due to blood transfusion but in India the authorities shy away from mandating NAT in the country. It is high time that we improve our blood safety levels and follow global best practices.

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