Hook Effect in Semiquantitative SARS-CoV-2 Antispike Total Antibody Assay.

Abstract

The hook effect is a common preanalytical error that results in falsely decreased analyte concentrations in immunoassays. We present here an example in a semiquantitative SARS-CoV-2 antispike total antibody assay and report the incidence of this error at our institution. All specimens with initial results within the reportable range of the assay were diluted. Results with higher results upon dilution were determined to have the hook effect. In a subset of specimens, these results were also confirmed as elevated on an alternative SARS-CoV-2 antibody assay. Over 1 month, 12 (9.1%) of 132 results were within the analytical measuring range of the assay. Of these, 11 showed the hook effect and required dilution to obtain accurate results. These represented 8.3% of our total testing volume. The hook effect was detected in a semiquantitative SARS-CoV-2 antispike total antibody assay at a high incidence. This error results in observed concentrations much lower than is accurate. Laboratories should be aware of this issue and consider manually diluting specimens within the reportable range of the assay to detect this issue.