Korean J Blood Transfus.  2015 Aug;26(2):204-212. 10.17945/kjbt.2015.26.2.204.

Application of a Grey Zone for HCV and HIV Immunoassays for Blood Donor Screening: Is It still Necessary?

  • 1Central Blood Laboratory Center, Seoul, Korea.
  • 2Seoul Nambu Blood Center, Korean Red Center, Seoul, Korea. sykwon@redcross.or.kr
  • 3Blood Transfusion Research Institute, Korean Red Center, Wonju, Korea.
  • 4Seoul Seobu Blood Center, Korean Red Cross, Seoul, Korea.


When enzyme immunoassays (EIA) were implemented, considering the limited sensitivity of 1st generation EIAs, the Korean Red Cross (KRC) applied grey zones for detection of weak reactive samples that could lead to false negative results. Despite improved performance of assays, grey zone application is still in practice. We examined whether application of a grey zone to HCV and HIV EIAs is still necessary.
HCV and HIV EIA results, number of grey zone results, results of further testing done on grey zone samples, and NAT results from 2005 to 2012 were analyzed retrospectively using the Blood Information Management System of the KRC.
Among 18,736,094 cases tested, 4,817 HCV (0.03%) and 5,108 HIV (0.05%) cases repeatedly had grey zone results. Twenty-eight (0.58%) HCV grey zone cases were positive on the recombinant immunoblot assay, but negative on NAT. For HIV, 3 cases were diagnosed as indeterminate by the Korea Centers for Disease Control and Prevention (KCDC). However these cases did not seroconvert after several years and were also negative on NAT.
For HCV, since the grey zone led to detection of true anti-HCV positive cases, not detected by NAT, application of the grey zone should be continued. For HIV, since none of the grey zone cases has been diagnosed as HIV positive by the KCDC, further application of the grey zone is thought not to be necessary. Re-evaluation of the grey zone will save costs for testing, and prevent discard of blood components and loss of donors.


Enzyme immunoassay; Grey zone; HCV; HIV
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