Analysis of SARS-CoV-2 RT-qPCR Ct values vis-Ã -vis anti-SARS-CoV-2 antibodies from a high incidence region

Markewitz, Robert; Torge, Antje; Wandinger, Klaus-Peter; Pauli, Daniela; Dargvainiene, Justina; Franke, Andre; Bujanda, Luis; Marimón, José Maria; Banales, Jesus M.; Gutierrez-Stampa, María A.; Nafría, Beatriz; Junker, Ralf

OBJECTIVES: To examine the relationship between antibody status and Ct values and the prognostic value of the latter for COVID-19 patients, and the inter-assay comparability of SARS-CoV-2 Ct values. METHODS: In 347 COVID-19 inpatients, SARS-CoV-2 Ct values (via RT-qPCR) on admission were compared in between two assays and correlated with the antibody response (in the course of the disease), the clinical course and the time since onset of symptoms. RESULTS: Ct values for two of three target genes showed significant differences between the two assays used (p=0.012 and p<0.0001). Ct values were significantly higher for antibody positive patients (p<0.0001). Ct values were positively correlated with the amount of time since onset of symptoms (R: 0.332-0.363; p<0.001). Patients with fatal outcomes showed higher viral loads than survivors (p<0.0001). CONCLUSIONS: Ct values depend strongly on the assay used and the target gene examined and should not be used as quantitative values to guide therapeutic or diagnostic decisions. The inverse association between the antibody status and the viral load suggests that antibodies contribute to the elimination of the virus, independent of the outcome, which is influenced by the viral load on admission and might depend more strongly on other parts of the immune response.