For thrombosis, the clinical diagnosis was confirmed by objective methods (computed tomography scanning, magnetic resonance imaging, electrocardiographic studies and elevated levels of cardiac enzymes, Doppler ultrasonographic scan, ventilation-perfusion scanning and pulmonary angiography)

For thrombosis, the clinical diagnosis was confirmed by objective methods (computed tomography scanning, magnetic resonance imaging, electrocardiographic studies and elevated levels of cardiac enzymes, Doppler ultrasonographic scan, ventilation-perfusion scanning and pulmonary angiography). This study was conducted in accordance with the principles of the Declaration of Helsinki. least 12 weeks was drawn to test the persistence of aPL. Results One hundred and fifty-eight patients (59.5% men) with a mean age of 61.4 14.9 years old were included. Thrombosis was present in 28 (17.7%) patients, severe Hexanoyl Glycine respiratory failure in 47 (30.5%), and 30 (18.9%) patients were admitted to ICU. Sixteen (28.6%) patients were positive for the criteria aPL at both determinations and only two (3.6%) of them suffered from thrombosis during hospitalisations (both had aCL IgG). However, they presented with low titers of aCL. Of note, aPL were not related to thrombosis, ICU admission or severe respiratory failure. Conclusion Although aPL were prevalent in our cohort of hospitalised COVID-19 patients and they were persistent in half of tested patients, most determinations were at low titers and they were not related to Hexanoyl Glycine worse clinical outcomes. Keywords: COVID – 19, antiphospholipid antibodies, antiphospholipid syndrome – immunology, diagnosis, thrombosis – immunology, persistence, severe respiratory failure Introduction The coronavirus disease (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was first identified in Wuhan, China in December 2019, and rapidly spread globally, leading to a worldwide pandemic (1). Several reports have described a hypercoagulable state, as well as significant changes in haemostatic laboratory parameters (2, 3). Early reports of COVID-19 already suggested that elevated circulating D-dimer levels might be associated with increased mortality (3). Furthermore and supporting this hypothesis, an autopsy series report demonstrated the presence of fibrin thrombi within distended small vessels and capillaries in the lungs and heart (4). Since a first small case series report in China (5), several works have described the prevalence of antiphospholipid antibodies (aPL) and their possible association with the development of thrombosis and complications in COVID-19 patients. However, in most studies aPL were measured only at a single timepoint, and information about the methods and quantitative results is scarce. Data from a recent metanalysis revealed that the pooled prevalence rate of one or more aPL – including IgG or IgM isotypes of anticardiolipin (aCL) or anti-2glycoprotein I (a2GPI) Hexanoyl Glycine or anti-phosphatidylserine/prothrombin antibodies (aPS/PT) or lupus anticoagulant (LAC) – was 46.8% (6). The LAC was the most frequently detected, with pooled prevalence rate of 50.7%, followed by aCL (IgM or IgG) Hexanoyl Glycine and a2GPI (IgM or IgG), with a pooled prevalence rate of 13.9% and 6.7%, respectively (6). Only two studies have retested patients and found a change from positive to negative aPL in almost all the analysed patients suggesting that aPL may be transiently elevated in patients with COVID-19 (7, 8). Findings are contradictory on the relationship between CFD1 aPL and hospital outcomes such as mortality, invasive ventilation or venous thrombosis. According to the previous metanalysis, aPL were not significantly associated with the worse clinical outcomes (6). Given the various gaps in the current understanding of aPL in patients with COVID-19, we aimed to characterise patterns of aPL testing and to describe the clinical course of complications and transient changes of laboratory findings during hospitalisation in a cohort of COVID-19 patients. Patients and Methods Patients We conducted a prospective study including consecutive hospitalised patients with COVID-19 from Hospital Clnic of Barcelona between March 28th and April 22nd, 2020. Inclusion criteria were patients aged 18 or older with either suspected (based on clinical, epidemiological and radiological findings) or Hexanoyl Glycine confirmed (by reverse transcriptase-polymerase chain reaction (RT-PCR) on a nasopharyngeal swab) COVID-19. Clinical data including demographic variables and comorbidities such as arterial hypertension, diabetes mellitus, obesity, and previous thrombosis were collected. Clinical outcomes during hospitalisation were also recorded. These comprised thrombotic events, intensive care unit (ICU) admission and severe ventilatory failure defined as the ratio of arterial oxygen partial.