Defining ELISpot cut-offs from unreplicated test and control wells.
Alexander, Neal;
Fox, Annette;
Lien, Vu Thi Kim;
Dong, Tao;
Lee, Laurel Yong-Hwa;
Hang, Nguyen Le Khanh;
Mai, Le Quynh;
Horby, Peter;
(2013)
Defining ELISpot cut-offs from unreplicated test and control wells.
Journal of immunological methods, 392 (1-2).
pp. 57-62.
ISSN 0022-1759
DOI: https://doi.org/10.1016/j.jim.2013.02.014
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In the absence of replication of wells, empirical criteria for enzyme-linked immunospot (ELISpot) positivity use fixed differences or ratios between spot forming units (SFU) counts between test and control. We propose an alternative approach which first identifies the optimally variance-stabilizing transformation of the SFU counts, based on the Bland-Altman plot of the test and control wells. The second step is to derive a positivity threshold from the difference in between-plate distribution functions of the transformed test and control SFU counts. This method is illustrated using 1309 assay results from a cohort study of influenza in Vietnam in which some, but not all, of the peptide pools have clear tendencies for SFU counts to be higher in test than control wells.