Effect of grey zone sample testing of transfusion transmissible infectious diseases on safety of blood-experience of a tertiary care referral teaching hospital blood bank from South India

Anitha M., Sreedhar Babu K. V., Praveen M. D., Sriranjitha T. V. N.


Background: Grey zone samples with optical density (OD) lying between cut-off OD and 10% below the cut-off OD (cut-off OD × 0.9) were identified during routine transfusion transmissible infectious disease (TTIs) screening. Enzyme-linked immunosorbent assay (ELISA) used for this purpose can sometimes fail to detect blood donors who are recently infected or possessing the low viremia. Estimation of a grey zone in ELISA testing and repeat testing of grey zone samples can further help in reducing the risks of TTI in countries where nucleic acid amplification testing for TTIs is not feasible.

Methods: On performing repeat ELISA testing on grey zone samples in duplicate, the samples showing both OD values below grey zone were marked nonreactive, and samples showing one or both OD value in the grey zone were marked indeterminate. The samples on repeat testing showing one or both OD above cut-off value were labelled reactive.

Results: Of the 21,908 blood donors screened during the study period, a total of 144 blood donors were found to be in grey zone. On repeat testing of these grey zone samples, 35 (24.30%) were found to be reactive for TTIs.

Conclusions: Estimation of grey zone samples with repeat testing can further enhance the safety of blood transfusion in resource poor developing nations where more sophisticated and sensitive methods such as nucleic acid amplification test (NAT) is not available in all the blood banks.


Enzyme linked immunosorbent assay, Grey zone, Transfusion transmissible viral infections

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