This document discusses nucleic acid amplification testing (NAT) for screening donated blood. It notes that NAT provides several advantages over traditional serological testing by detecting infections in the "window period" before antibodies are present. Specifically, NAT can reduce the risk of transmitting HIV, hepatitis B, and hepatitis C through blood transfusions. While NAT improves safety, it is not a replacement for serological screening and must be used together with existing antibody-based tests. The document also provides details on how NAT is currently implemented in Sri Lanka and the specific assays used.

1. Nucleic Acid
Amplification Testing
DR. G.D.A. SAMARANAYAKA
REGISTRAR IN TRANSFUSION MEDICINE
NATIONAL BLOOD TRANSFUSION SERVICE

2. Blood Safety
• Both donor and recipient
• Voluntary non remunerated blood donors
• Pre donation information to blood donors
• Donor counselling and examination – donor
declaration form
• TTI testing
• Pathogen inactivation
• Patient blood management

3. Transfusion transmitted infection testing
• Mandatory screening required by theWHO
• HIV 1 & 2
• Hepatitis B and C
• Malaria
• Syphilis
• Depending on the prevalence – HTLV, WNV, Leishmania etc.

4. Testing Methodologies
• Microscopical examination – Malaria
• Serological testing
• ELISA,Chemiluminescence (ECi), Rapid testing
• Particle agglutination/Hemagglutination – (TTPA,TPHA,
HIV)
• Antibody detection & Antigen detection
• NAT testing

5. TTI screening testing done in Sri Lanka
• Hepatitis B surface antigen (HBsAg)
• Hepatitis B core antibody (anti-HBc)
• Hepatitis C virus antibody (anti-HCV)
• HIV-1 and HIV-2 antibody (anti-HIV-1 and anti-HIV-2) + p24 antigen
• Malaria – thick and thin films – microscopic examination
• Treponema pallidum –VDRL /TPPA

6. What is NAT?
• NucleicAcid Amplification Testing
• A generic term that include a number of different technologies
• extraction or capture of nucleic acid, amplification, and
detection
• Types – ID NAT & MP NAT

7. Introduction of NAT – timeline

8. Window Period
• Period between the initial infection and the time
at which the presence of the virus or bacteria can
first be identified in the blood (by detecting
antibodies, antigens, DNA or RNA).
 Eclipse phase - the very initial phase after
exposure when virus replication is restricted to
tissue sites and there is no detectable viraemia
 Infectious phase - is after eclipse and before
seroconversion

9. Importance of the window period
• During the window period - pathogen cannot be detected
• Could transmit the infection via transfusion
• Infection of transfusion recipients

10. HIV

11. Hepatitis B

12. Hepatitis C

13. Why NAT testing is important

14. Residual risk
Major sources of remaining risk are:
1. Window period donation
2. Viral variants not detect by current assays
3. Immunosilent donor
4. Laboratory testing error

15. NAT implementation in Sri Lanka
• Since 2012
• Started as a pilot project
• Testing performed for 30-40% of the total blood collection
• Using ProcleixTigris system
• Procleix Ultrio Elite Screening assey
• Procleix Ultrio Elite HIV, HCV, and/or HBV DiscriminatoryAssays

16. Procleix® Ultrio Elite Assay
• 1) Sample preparation/ target capture
• 2) HIV RNA, HCV RNA, and HBV DNA target
amplification byTranscription-Mediated
Amplification (TMA)
• 3) Detection of the amplification products
(amplicon) by the Hybridization Protection
Assay (HPA).

17. Advantages
• Significant reduction of window period and residual risk
• Improved blood safety
• Rapid implementation of testing for various transfusion transmissible
pathogens –WNV
• Detection of novel pathogens

18. Disadvantages
• Highly technically demanding
• High costs
• Need of dedicated infrastructure facility, equipment, consumables
and technical expertise
• May not detect some mutated strains

19. Will NAT replace serological testing?
• NO
• Small percentage of Antibody positive donors have been tested
negative by NAT tests.
• It is possible that an antibody positive and NAT Negative donation
might transmit infection to the recipient.
• Therefore NATTesting will not replace current serology tests in blood
screening
• So far no country has discontinued the serology screening for HBsAg,
Anti HIV and Anti HCV after implementation of NAT screening

20. ThankYou