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Background: The novel coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has spread across the world. The aim of our study was to characterize mild courses and to determine the antibody status for these patients., Methods: We initiated an appeal for convalescent plasma donations. 615 people contacted us, and we ultimately included 426 in our analyses, in whom it was possible to assume COVID-19 based on detection of specific SARS-CoV-2 antibodies or virus detection during the disease using RT-PCR., Results: The median duration of the disease was 12 days and the most common symptoms were fatigue, cough and olfactory and gustatory dysfunction. Anti-SARS-CoV-2 IgG was detected in 82.4% of the persons and IgA antibodies were found in 73.9%. In 10.8%, no antibodies were detectable despite a positive RT-PCR result during the disease. Nevertheless, of 24 persons with asymptomatic courses of COVID-19, antibodies against SARS-CoV-2 could be detected in 23 (96%). Furthermore, there was a correlation between the duration of the disease and the detection of IgG antibodies. In addition, a correlation between the determined IgG antibodies and neutralizing antibodies was shown., Conclusion: In this study, we were able to describe mild COVID-19 courses and determine antibody statuses for them. It could be shown that, despite SARS-CoV-2 detection during the disease, not all individuals developed antibodies or their level of antibodies had dropped below the detection limit shortly after the end of the disease. The extent to which immunity to re-infection is given in persons with undetectable antibodies (IgG, IgA) needs to be investigated in future studies., Competing Interests: I have read the journal’s policy and the authors of this manuscript have the following competing interests: Ingvild Birschmann received speaker’s honoraria from Aspen Germany GmbH, Bristol-Myers Squibb/Pfizer, Siemens Healthcare and CSL Behring and reimbursement for congress traveling and accommodation from aspen and performed contract research for Siemens Healthcare. Ingvild Birschmann is a member of the advisory board of LFB biomedicaments, Siemens Healthcare and CSL Behring. Tobias Flieder, Tanja Vollmer, Benjamin Müller, Jens Dreier, Bastian Fischer and Cornelius Knabbe have nothing to disclose. This does not alter our adherence to PLOS ONE policies on sharing data and materials.

Introduction: The fast, precise, and accurate measurement of the new generation of oral anticoagulants such as dabigatran and rivaroxaban in patients' plasma my provide important information in different clinical circumstances such as in the case of suspicion of overdose, when patients switch from existing oral anticoagulant, in patients with hepatic or renal impairment, by concomitant use of interaction drugs, or to assess anticoagulant concentration in patients' blood before major surgery., Methods: Here, we describe a quick and precise method to measure the coagulation inhibitors dabigatran and rivaroxaban using ultra-performance liquid chromatography electrospray ionization-tandem mass spectrometry in multiple reactions monitoring (MRM) mode (UPLC-MRM MS). Internal standards (ISs) were added to the sample and after protein precipitation; the sample was separated on a reverse phase column. After ionization of the analytes the ions were detected using electrospray ionization-tandem mass spectrometry. Run time was 2.5 minutes per injection. Ion suppression was characterized by means of post-column infusion., Results: The calibration curves of dabigatran and rivaroxaban were linear over the working range between 0.8 and 800 μg/L (r >0.99). Limits of detection (LOD) in the plasma matrix were 0.21 μg/L for dabigatran and 0.34 μg/L for rivaroxaban, and lower limits of quantification (LLOQ) in the plasma matrix were 0.46 μg/L for dabigatran and 0.54 μg/L for rivaroxaban. The intraassay coefficients of variation (CVs) for dabigatran and rivaroxaban were < 4% and 6%; respectively, the interassay CVs were < 6% for dabigatran and < 9% for rivaroxaban. Inaccuracy was < 5% for both substances. The mean recovery was 104.5% (range 83.8-113.0%) for dabigatran and 87.0% (range 73.6-105.4%) for rivaroxaban. No significant ion suppressions were detected at the elution times of dabigatran or rivaroxaban. Both coagulation inhibitors were stable in citrate plasma at -20°C, 4°C and even at RT for at least one week. A method comparison between our UPLC-MRM MS method, the commercially available automated Direct Thrombin Inhibitor assay (DTI assay) for dabigatran measurement from CoaChrom Diagnostica, as well as the automated anti-Xa assay for rivaroxaban measurement from Chromogenix both performed by ACL-TOP showed a high degree of correlation. However, UPLC-MRM MS measurement of dabigatran and rivaroxaban has a much better selectivity than classical functional assays measuring activities of various coagulation factors which are susceptible to interference by other coagulant drugs., Conclusions: Overall, we developed and validated a sensitive and specific UPLC-MRM MS assay for the quick and specific measurement of dabigatran and rivaroxaban in human plasma.