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Background and Objectives: In this study, the performance of three different commercial antibody assays for COVID-19 was examined and parameters affecting the antibody response were investigated. The correlation of patients’ chest CT results, procalcitonin, CRP, and D-dimer levels with the antibody response were retrospectively evaluated. Materials and Methods: COVID-19 antibodies were detected by three commercially available assays in each patient. Two of the assays were rapid immunochromatographic tests and - one was an ELISA-based IgG assay. SARS-CoV-2 RNA was tested by “COVID-19 RT-qPCR Detection Kit” using nasopharyngeal swab samples. The results of antibody tests were com- pared with each other, RT-qPCR, Biochemical parameters and chest CT findings. Results: RT-qPCR was positive in 46.6% (41/88) of the evaluated patients among which 77.3% (68/88) were healthcare workers. Seventeen (41.4%) of viral RNA positive patients had a positive antibody result with at least two assays. Both of the rapid immunochromatographic tests had identical sensitivity of 36.6% and specificity of 100%, compared to RT-qPCR assay; while the sensitivity of the ELISA based Euroimmune test was 43.9%, and the specificity was 95.7%. The sensitivity and specificity of the immunochromatographic tests were 75% and 100% respectively, compared to ELISA test result. There was a correlation between antibody positivity and old age and male gender. The presence of typical chest CT findings increased the antibody positivity 13.62 times. Antibody positivity was also increased with the decrease in Ct value of the PCR assay. There was no significant relationship between the biochemical parameters (CRP, D-dimer and procalcitonin values) and the antibody or RT-qPCR results. Conclusion: There was a correlation between antibody response and male gender, older age, presence of symptoms, typical chest CT findings and low PCR-Ct value.

INTRODUCTION Following the announcement of first coronavirus disease 2019 (COVID‐19) case on March 11, 2020, in Turkey we aimed to report the co‐infection rates, and the clinical, laboratory, radiological distinctive features of viral pneumonia caused by viruses other than severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2). METHODS A cross‐sectional study was conducted between 18 and 31 March 2020. COVID‐19 suspected cases admitted to pandemic policlinic who had nasopharyngeal swab specimens tested for both SARS‐CoV‐2 and other respiratory viral pathogens were included. RESULTS Within 112 patients SARS‐CoV‐2 was detected in 34 (30%). Among the non‐SARS‐CoV‐2 viruses (n=25, 22%), metapneumovirus (n=10), was the most frequent agent. There were two co‐infections with SARS‐CoV‐2. Sputum was less in the SARS‐CoV‐2 group (p=0.003). The leukocyte, lymphocyte, and thrombocyte count and C‐reactive protein levels were lowest in the SARS‐CoV‐2 group (p