Interpretation of low reactivity in the Abbott Architect rHTLV I/II assay.

OBJECTIVE: The objective of this study is to reduce donor tissue wastage.

AIM: The aim of this study is to determine, in the case of the Abbott Architect rHTLV I/II assay, whether a signal/cut-off (S/CO) ratio higher than the manufacturer's recommendation of 1·0 could be applied to diagnose significant HTLV-1 seroreactivity.

BACKGROUND: The detection of human T cell leukaemia virus type 1 (HTLV-1) infection is primarily based on serology often utilising random access platforms. Although current assays have high sensitivity and specificity, in low-prevalence regions, significant numbers of false-positive reactions occur. A comprehensive follow-up is difficult within the time frame of organ donation. This can lead to donor tissue wastage.

METHODS: A retrospective analysis of 12 250 samples previously tested on the Abbott Architect rHTLV I/II platform and further tested by confirmatory serology/molecular detection to determine the sensitivity and positive predictive value in the S/CO ratio range was conducted.

RESULTS: Where the sample S/CO ratio was >20 (n = 498), HTLV infection was confirmed in all but eight subjects. All of these eight had indeterminate confirmatory results, and none were found to be uninfected. Conversely, in the samples within the S/CO ratio range 1-4 (n = 271), no subject was subsequently found to be HTLV-infected although HTLV infection could not be excluded in all cases, primarily due to lack of follow-up samples (n = 60/271).

CONCLUSIONS: Samples with an S/CO ratio of <4·0 on the Abbott Architect rHTLV I/II platform represent a low risk of HTLV infection in the UK, and organs from such donors might reasonably be considered for transplantation, within the context of appropriate risk-benefit assessment.