The sensitivity improved two-test algorithm “SIT2”: a universal optimization strategy for SARS-CoV-2 serology
Perkmann T., Koller T., Perkmann-Nagele N., Oszvar-Kozma M., Eyre DW., Matthews P., Bown A., Stoesser N., Breyer M-K., Breyer-Kohansal R., Burghuber OC., Hartl S., Aletaha D., Sieghart D., Quehenberger P., Marculescu R., Mucher P., Radakovics A., Klausberger M., Duerkop M., Holzer B., Hartmann B., Strassl R., Leitner G., Grebien F., Gerner W., Grabherr R., Wagner OF., Binder CJ., Haslacher H.
BackgroundReliable antibody tests are an essential tool to identify individuals who have developed an adaptive immune response to SARS-CoV-2. However, attempts to maximize the specificity of SARS-CoV-2 antibody tests have come at the cost of sensitivity, exacerbating the total test error with increasing seroprevalence. Here, we present a novel method to maximize specificity while maintaining or even increasing sensitivity: the “Sensitivity Improved Two-Test” or “SIT²” algorithm.MethodsSIT² involves confirmatory re-testing of samples with results falling in a predefined retesting-zone of an initial screening test, with adjusted cut-offs to increase sensitivity. We verified and compared the performance of SIT² to single tests and orthogonal testing (OTA) in an Austrian cohort (1,117 negative, 64 post-COVID positive samples) and validated the algorithm in an independent British cohort (976 negatives, 536 positives).ResultsThe specificity of SIT² was superior to single tests and non-inferior to OTA. The sensitivity was maintained or even improved using SIT² when compared to single tests or OTA. SIT² allowed correct identification of infected individuals even when a live virus neutralization assay could not detect antibodies. Compared to single testing or OTA, SIT² significantly reduced total test errors to 0·46% (0·24-0·65) or 1·60% (0·94-2·38) at both 5% or 20% seroprevalence.ConclusionSIT² proved to be the best diagnostic choice at both 5% and 20% seroprevalence in all tested scenarios. It is an easy algorithm to apply to different available SARS-CoV-2 antibody testing systems and can potentially be helpful for the serology of other infectious diseases.