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Year : 2011  |  Volume : 54  |  Issue : 2  |  Page : 433-434
Fourth-generation enzyme immunoassays for screening of HIV in blood donors: Need of the hour

Department of Transfusion Medicine, Government Medical College and Hospital, Chandigarh, India

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Date of Web Publication27-May-2011

How to cite this article:
Kaur R, Basu S, Kaur G, Singh D. Fourth-generation enzyme immunoassays for screening of HIV in blood donors: Need of the hour. Indian J Pathol Microbiol 2011;54:433-4

How to cite this URL:
Kaur R, Basu S, Kaur G, Singh D. Fourth-generation enzyme immunoassays for screening of HIV in blood donors: Need of the hour. Indian J Pathol Microbiol [serial online] 2011 [cited 2022 Oct 1];54:433-4. Available from:


Early diagnosis of infection with human immunodeficiency virus (HIV) is critical for ensuring the safety of blood products. Despite the use of stringent criteria for donor selection and improved blood safety measures, there is still a residual risk of transmitting viral infection due to window period. The new screening assays for HIV, that is, 4th-generation enzyme immunoassays (EIA) and nucleic acid testing (NAT) have improved the reliability of serologic laboratory diagnosis and significantly reduced the residual risk due to window period infection. In western countries, with the implementation of NAT the residual risk of HIV has significantly been reduced from 1 in 450,000 to 1 in 3 million. [1]

The majority of blood banks in the developing countries, such as India, are still performing 3rdgeneration EIA for screening of HIV in blood donors. Combined antigen-antibody (Ag-Ab) assay could be a reasonable and viable alternative for blood donor screening to reduce the residual risk. We evaluated the 4th-generation combo Ag-Ab EIA for screening of HIV in blood donors in comparison with the currently used 3rd-generation Ab EIA.

A total of 1075 samples of blood donors were analyzed by both 3rd-generation EIA (Microlisa HIV Ab, J. Mitra and Co, New Delhi, India) and 4th-generation EIA (Genscreen HIV Ag-Ab Ultra, BIO-RAD, Paris, France). [Table 1] shows the results. Confirmation by Western blot (WB) (J. Mitra and Co, New Delhi, India) test was done on all samples reactive by one assay and nonreactive with the other assay. In all, four samples were reactive by the 4th-generation EIA and nonreactive by the 3rd-generation EIA. Of the four samples, one sample was confirmed positive for HIV (1 and 2) by WB.
Table 1: Results of 3rd- and 4th-generation enzyme immunoassays

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Ag-Ab combo assays reduce the diagnostic window period compared with that of third-generation assays. This is due to the detection of HIV core protein (p24Ag) that appears transiently in blood donors prior to seroconversion. In the present study, 4 samples were reactive by 4th-generation EIA and nonreactive by 3rd-generation EIA. Of these one was confirmed positive by WB analysis. This led to the prevention of transfusion of three HIV-infected blood products from the one donation. Our center has approximately 12,000 annual collections and currently 3rd-generation EIA are being used for HIV screening in blood donors. With the current practice we may not identify infectivity in an estimated 12 donor units, which could lead to transfusion of 36 (12 × 3) HIV-infected products.

The study has its own limitations. The sample size is very small. Moreover, three samples tested negative by WB cannot be labelled as false positive by 4th-generation EIA because further confirmation by NAT was not done.

In the present study, four additional samples were picked up by 4th-generation EIA of which one was confirmed positive by WB analysis. This resulted in the prevention of transmission of HIV infection to three patients. As per WHO recommendation for HIV testing, in addition to the detection of antibody, the screening assay should preferably also employ the detection of antigen as detection of HIV p24 antigen reduces the serologic window period by 3-7 days. [2]

Addition of NAT for HIV RNA to a HIV screening algorithm reduces the window period to 7-11 days, but setting up a NAT laboratory in a developing country, such as India, is difficult due to its high cost and need of elaborate infrastructure, equipment, and trained manpower. Since the price of 4th-generation assay is in the same range as that of 3rd-generation HIV screening assays and there is no need for additional equipment or manpower, the safety of blood donor screening may be improved without additional cost.

   References Top

1.Busch MP. Transfusion transmitted viral infections: Building bridges to transfusion medicine to reduce risks and understand epidemiology and pathogenesis. Transfusion 2006;46:1624-40.  Back to cited text no. 1
2.Kitchen A, Dax EM, Reddy R, Dhingra N, Fordham J, Lloyds S. Screening donated blood for transfusion transmissible infections: Recommendations. Available from: [published in 2009] [accessed in 2010 Sept].  Back to cited text no. 2

Correspondence Address:
Ravneet Kaur
Department of Transfusion Medicine, Government Medical College and Hospital, Chandigarh
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0377-4929.81623

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[Pubmed] | [DOI]


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