Patients
We included all patients ≥18 years old with confirmed COVID-19 admitted
to one of the six participating hospitals in the Netherlands (1 academic
hospital (Radboudumc, Nijmegen), 5 general hospitals (Bernhoven
hospital, Uden; Sint Maartenskliniek, Nijmegen; Canisius Wilhelmina
hospital, Nijmegen; Rijnstate hospital, Arnhem; Jeroen Bosch hospital,
‘s-Hertogenbosch)) between March 1 and May 31, 2020. The diagnosis
COVID-19 was made with a real-time reverse transcriptase polymerase
chain reaction (RT-PCR) positive for SARS-CoV-2 on a deep
naso-oropharyngeal swab. In addition, patients with negative PCR but
with clinical symptoms consistent with COVID-19 and a CT-scan of the
chest showing a very high suspicion of typical pulmonary involvement of
COVID-19 (COVID-19 reporting and data system score of 5 defined by the
Dutch Radiology Society) were included.29 Patients
were excluded when COVID-19 was not RT-PCR or radiographically
confirmed, or when patients had insufficient clinical documentation
because they were transferred to or from another hospital due to
capacity constraints.
The index date was the day of hospital admission. Patients were followed
until hospital discharge or death. Data on the occurrence of thrombotic
events, length of hospital stay, ICU admission, type of oxygen
ventilation, and mortality were obtained from the patients’ records
(EPIC, EPIC Systems Corporation, Verona, Wisconsin, USA; HiX, ChipSoft,
Amsterdam, The Netherlands; xCare EPD, NEXUS, Nieuwegein, The
Netherlands) and recorded in our database using a standardized case
report form in the good clinical practice (GCP)-compliant data
management system Castor (Castor Electronic Data Collection, Amsterdam,
the Netherlands). CT pulmonary angiograms (CTPAs) and Doppler
ultrasonography were performed at the discretion of the treating
clinician. Common indications for CTPA included high D-dimer levels
and/or progressive hypoxemia. The study was carried out in the
Netherlands in accordance with the applicable rules concerning the
review of research ethics committees and informed consent. The
Institutional Review Boards of the participating hospitals waived the
need for informed consent due to the observational nature of this study.