Current approaches to improve the safety of the blood supply
- Donor selection
- Serological and nucleic acid testing
- Bacterial detection
- Gamma irradiation
Tests performed on donated blood
* NAT testing is not performed in all countries
- 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)
- HTLV-I and HTLV-II antibody (anti-HTLV-I and anti-HTLV-II)
- Serologic test for syphilis
- Nucleic acid amplification testing (NAT) for HIV-1 and HCV*
- NAT for WNV**
** Only in the USA
Infectious risk of blood products
Due to stringent donor selection and testing procedures, fresh-frozen plasma (FFP) in the developed world offers a high degree of viral safety.
Bibliography: Germany: Offergeld et al Euro Surveill 2005;10(2):8-11 (Data from 2000-2002), UK: Soldan et al Euro Surveill 2005;10(2):17-19 (data from 2002-2003), Switzerland: Niederhauser et al Euro Surveill.2005;10(2):14-16 (data from 1996-2003), France: Pillonel Euro Surveill 2005;10(2):5-8 (data from 1992-2003), Canada: MacDonald et al: Paediatr Child Health Vol 11 No 3 March 2006, USA: Dodd et al Transfusion 2002;42(8):975-979
However, the current strategy can not eliminate all transfusion-transmitted infectious agents, i.e.not only known pathogens but also unknown new agents, and some patients may be harmed before preventive measures are introduced.
The window period
This is the period between the moment of 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). During the window period, the blood of a donor may be infectious, although the screening test does not indicate this. This means that the negative result of the screening test is then actually incorrect.
The average window period (using the current serologic methods)
- For HIV is 22 days (between days 6 – 38),
- For HBV is 59 days (between days 37 – 87)
- For HCV is 82 days (between days 54 – 194).
Nucleic-acid-amplification testing (NAT)
The window periods for HIV, HBV and HCV have been considerably shortened due to the introduction of nucleic-acid-amplification testing (NAT), which screens for the virus itself and not for antibodies directed against it. Virus infections are detected by NAT much sooner after infection. This very sensitive technique is able to detect very small amounts of viral RNA or DNA, even when serological tests are negative. The principle of this technique is that the RNA or DNA present is selectively increased, after which detection can take place.
Although NAT reduces the window period it has its own limitations: – Sensitivity : Minipool PCR is not able to detect very low titer viruses. This has led to transmission of HIV, HBV and HCV.* – Specificity :
MPNAT : mini pool NAT SDNAT: single donation NATBibliography : *M.K. Hourfar, C. Jork, V. Schottstedt, M. Weber-Schehl, V. Brixner, M.P. Busch, G. Geusendam, K. Gubbe, C. Mahndart, U. Mayr-Wohlfart, L. Picl, W.K. Roth, M. Schmidt, E. Seifried, and D.J. Wright Experience of the German Red Cross blood donor services with nucleic acid testing: results of screening more than 30 million blood odnations for human immunodeficiency virus-1, hepatitis C virus, and hepatitis B virus. Transfusion; Vol.48, August 2008; 1558:1566 **B.R. Jackson, M.P. Busch, S.L. Stramer, and J.P. AuBuchon. The cost-effectiveness of NAT for HIV, HCV,and HBV in whole-blood donations. Transfusion; Vol.43, June 2003; 721:729
Time length for screening test development
Historically, there has been a very long interval between the first recognition that a disease is transfusion-transmitted and the eventual implementation of a donor-screening test to prevent that transmission.