Preanalytical stability of SARS-CoV-2 anti-nucleocapsid antibodies.

Abstract

Anti-nucleocapsid (NC) antibodies are produced in response to SARS-CoV-2 infection. Therefore, they are well suited for the detection of a previous infection. Especially in the case of seroprevalence studies or during the evaluation of a novel in-vitro diagnostic test, samples have been stored at <-70°C (short- and long-term) or 2-10°C (short-term) before analysis. This study aimed to assess the impact of different storage conditions relevant toroutine biobanking on anti-NC antibodies. The preanalytical impact of short-term storage (84 [58-98] days) on <-70°C and for 14days at 2-10°C was evaluated using samples from 111 donors of the MedUni Vienna Biobank. Long-term effects (443 [409-468] days) were assessed using 208 samples from Biobank Graz and 49 samples from Biobank Vienna. Anti-Nucleocapsid antibodies were measured employing electrochemiluminescence assays (Roche Anti-SARS-CoV-2). After short-term storage, the observed changes did not exceed the extent that could be explained by analytical variability. In contrast, results after long-term storage were approximately 20% higher and seemed to increase with storage duration. This effect was independent of the biobank from which the samples were obtained. Accordingly, the sensitivity increased from 92.6 to 95.3% (p=0.008). However, comparisons with data from Anti-Spike protein assays, where these deviations were not apparent, suggest that this deviation could also be explained by the analytical variability of the qualitative Anti-NC assay. Results from anti-NC antibodies are stable during short-term storage at <-70°C and 2-10°C. After long-term storage, a slight increase in sensitivity could notbe ruled out.