Effect of Grey Zone Samples Testing by Enzyme Immunoassay and Its Impact on Enhancing Blood Safety: Experience from Tertiary Care Hospital based Blood Bank in Central Gujarat
Keywords:ELISA, Grey Zone, Transfusion transmitted infection,
Background : Enzyme linked immunosorbent assay is a standard protocol adopted by majority of Blood
Banks for screening of blood units for transfusion transmissible infections. The grey zone testing of samples
increases sensitivity of ELISA tests which in turn enhances the safe blood transfusion practices. The present
study was thus designed to know the effect of repeat testing of Grey zone Blood Donor samples for
improving the sensitivity of ELISA Screening methods in blood banks.
Methods:- All Blood Donor Samples which were 10% below the cut- off value were marked as Grey zone
samples and were repeated for ELISA screening . Interpretation of Repeat tests was done as per NACO and
WHO guidelines and the samples which recorded their one or both O.D value above cut- off were labelled
as reactive and samples which recorded one or both O.D value in grey zone were marked as indeterminate.
Results and Conclusion: In present study, a total of 10,425 Blood Donors were screened for TTI’ s and
out of 10,425 (15) Blood donor samples were found in grey zone. The results of repeat testing showed that
9 (60%) Blood Donor samples were found to be confirm reactive for TTI. Grey zone sample testing should
be done routinely as a measure to enhance sensitivity of ELISA testing of Blood Donors in developing
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