A hepatitis C avidity test for determining recent and past infections in both plasma and dried blood spots

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Shepherd, Samantha J. and Keen, Joy and Hutchinson, Sharon and Cameron, Sheila O. and Goldberg, David J. and Carman, W. and Gunson, R.N. and Aitken, Celia (2013) A hepatitis C avidity test for determining recent and past infections in both plasma and dried blood spots. Journal of Clinical Virology, 57 (1). pp. 29-35. ISSN 1386-6532 (https://doi.org/10.1016/j.jcv.2013.01.002)

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Abstract

DBS testing has been used successfully to detect HCV antibody positive individuals. Determining how long someone has been infected is important for surveillance initiatives. Antibody avidity is a method that can be used to calculate recency of infection. A HCV avidity assay was evaluated for both plasma and DBS. Study design: To measure antibody avidity a commercial HCV ELISA was modified using 7 M urea. The plasma samples were split into: group 1 (recently infected N = 19), group 2 (chronic carrier N = 300) and group 3 (resolved infection N = 82). Mock DBS made from group 1 (N = 12), group 2 (N = 50), group 3 (N = 25) and two seroconverter panels were evaluated. 133 DBS taken from patients known to have a resolved infection or be a chronic carrier were also tested. The avidity assay cut-off was set at AI ≤ 30 for a recent infection. Using sequential samples the assay could detect a recent infection in the first 4–5 months from the point of infection. Most of the false positive results (AI < 30 among cases known not to have had recent infection) were detected among known resolved infections, in both the plasma and DBS; as a result, a testing algorithm has been designed incorporating both PCR and two dilution factors. The sensitivity and specificity of the assay on plasma was 100% and 99.3%, respectively, while DBS had 100% sensitivity and 98.3% specificity. The HCV avidity assay can be used to distinguish between chronic and recent infection using either plasma or DBS as the sample type.

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