title: Impact of grey zone sample testing by enzyme-linked immunosorbent assay in enhancing blood safety: Experience at a tertiary care hospital in North India.
abstract: BACKGROUND
  Enzyme-linked immunosorbent assay (ELISA) used for screening blood donors for transfusion transmitted infections (TTIs) can sometimes fail to detect blood donors who are recently infected or possessing the low strength of pathogen. 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
  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 ELISA testing. On performing repeat ELISA testing on grey zone samples in duplicate, the samples showing both OD value 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 marked positive.
  
  
  RESULTS
  About 119 samples (77 for hepatitis B virus [HBV], 23 for human immunodeficiency virus [HIV], and 19 for hepatitis C virus [HCV]) were found to be in grey zone. On repeat testing of these samples in duplicate, 70 (58.8%) samples (45 for HBV, 12 for HIV, and 13 for HCV) were found to be reactive. Six (5%) samples (four for HBV, one for HIV, and one for HCV) were found to be indeterminate.
  
  
  CONCLUSIONS
  Seventy donors initially screened negative, were found out to be potentially infectious on repeat grey zone testing. Thus, estimation of grey zone samples with repeat testing can further enhance the safety of blood transfusion.
authors.affiliation: Department of Transfusion Medicine, Sanjay Gandhi Post Graduate Institute of Medical Sciences, Dubagga, Lucknow, Uttar Pradesh, India.
authors.forename: Archana
authors.initials: A
authors.lastname: Solanki
authors.affiliation: Department of Transfusion Medicine, Charak Hospital and Research Centre, Dubagga, Lucknow, Uttar Pradesh, India.
authors.forename: Abhay
authors.initials: A
authors.lastname: Singh
authors.affiliation: Department of Transfusion Medicine, Sanjay Gandhi Post Graduate Institute of Medical Sciences, Dubagga, Lucknow, Uttar Pradesh, India.
authors.forename: Rajendra
authors.initials: R
authors.lastname: Chaudhary
keywords: Enzyme-linked immunosorbent assay; grey zone; transfusion transmitted infection