The study was conducted at the Vimercate Hospital, a 500 bed General Hospital located in Lombardy, northern Italy. From February to May 2020, 712 patients with a confirmed diagnosis of COVID-19 were hospitalized in our institution. Among them, 218 subjects have been admitted to the internal medicine department wards in April 2020.
In the first months of 2020, different reports suggesting an increasing risk of APE in COVID-19 patients were published [6-7]. Thus, in late march, a multidisciplinary group from our hospital issued an internal protocol with some recommendations to prevent and treat thrombotic complications in COVID-19 patients. The protocol strongly recommended performing a diagnostic CTPA to confirm or rule out APE in COVID-19 patients admitted to the internal medicine department wards presenting respiratory deterioration after admission, defined by a PaO2/FiO2 ratio reduction of > 30%.
Therefore, in the present retrospective cohort study we included all COVID-19 patients admitted to the internal medicine department (sub intensive and acute general beds of the internal medicine department wards) who had CTPA examinations performed from April 1st to April 31st for respiratory deterioration after admission, defined by a reduction of > 30% of the PaO2/FiO2 ratio. The exclusion criteria were: subjects with a story of bleeding diathesis and/or current use of anticoagulant therapy before hospitalization; age < 18, and critical COVID19 infection, defined by any of the following criteria a. respiratory failure needing mechanical assistance, b. shock c. “extra pulmonary” organ failure needing intensive care unit.
Electronic charts of all included patients were retrieved for evaluation. Trained study personnel retrospectively recorded relevant clinical, laboratory and treatment data. The diagnosis of COVID-19 was confirmed by RNA detection of the SARS-CoV-2.
Data of the following laboratory test performed upon admission have been collected: D-dimer, international normalized ratio (INR), c-reactive protein (CRP), white blood cell count (WBCC), lactate dehydrogenase (LDH), alanine transaminase (ALT), aspartate transaminase (ALT), Creatinine (Cr), arterial partial pressure of carbon dioxide (PaCO2), arterial oxygen partial pressure (PaO2), fraction of inspired oxygen (FiO2). Albumin, Interleukin 6, and Antithrombin III were measured within 24 hours of performing CTPA. D-dimer was measured by using HemosIL D-Dimer HS, a latex-enhanced turbidimetric immunoassay from Instrumentation Laboratory, on the fully automated coagulometer ACL TOP analyzer [16]. The normal value declared by the producer is less than 243 ng/mL [16].
Based on a retrospective chart review of clinical symptoms and patient history factors Wells score simplified version was calculated for each patient giving one point for the presence of each of the following items: (1) Previous PE or DVT; (2) Heart rate ≥100 b.p.m.; (3) Surgery or immobilization within the past four weeks; (4) Haemoptysis; (5) Active cancer (6); Clinical signs of DVT ; (7) Alternative diagnosis less likely than PE. Patients with < 2 point were categorized as PE unlikely and those with > 2 points PE likely [17]. Since CTPA was performed in subjects suspected by presenting APE in addition to COVID-19 as causing respiratory deterioration, the last item of Wells score (alternative diagnosis less likely than PE) was considered present (1 point) in all cases.
Pulmonary embolism was confirmed on the basis of the presence of a filling defect in one or more pulmonary arteries up to sub-segmental arteries in CTPA, as stated by certified radiologists belonging to the hospital team, at the time of the acquisition of images. Helical CTPA scans were performed on a Brilliance Philips CT scanner (Philips, Cleveland, OH, USA) which included 64-detector row capability.
This study was conducted in accordance with the amended Declaration of Helsinki. The protocol was approved by to the Local institutional review board, i.e. the Comitato Etico della Provincia Monza e Brianza. Waiver of written informed consent was granted due to the retrospective, observational design.
Statistical methods
Clinical characteristics and laboratory data were summarized by number and percentage for categorical variables and by median and interquartile range for numerical variables, in the whole study group and according to APE. To compare the different characteristics among patients with APE confirmed and APE excluded, Fisher exact test was used for categorical variables and Wilcoxon rank rum test was used for numerical variables.
To evaluate the diagnostic accuracy of D-dimer to predict APE, a ROC curve was fitted and the Area Under the ROC Curve (AUC) with pertinent 95% confidence interval (CI95%) was estimated. Optimal cut-off was obtained as the D-dimer value which maximizes both the specificity and the sensitivity. The diagnostic performance of different D-dimer cut-offs (standard cut-off: > 243 ng/mL, age adjusted cut off: patients’ age x 5, ROC curve best discriminating value: 2454 ng/mL) and Wells score (standard cut off: >2) was evaluated by computing the corresponding values of sensitivity and specificity, positive predictive value, negative predictive value with pertinent CI95%. Furthermore, four generalized linear regression models with binomial error and link log were fitted: the response was APE and the explanatory variable was a dichotomous variable discriminating patients with D-dimer value over the different cut offs or Wells score over 2. Results were reported as Relative Risk (RR) with corresponding CI95% and p-values.
All analyses were performed using R software version 4.0.0, with packages OptimalCutpoints, pROC and epiR added.