INTRODUCTION
The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) outbreak that began in Wuhan, China, in December 2019 rapidly spread worldwide, insofar as the World Health Organization has declared COVID-19 to be a pandemic and a public health emergency of international concern (1-4). Although the disease is typically associated with respiratory tract involvement, the virus also can affect other systems including hematological and cardiovascular systems through different hypothesized mechanisms (5, 6). One of the most important underlying mechanisms is an increased level of inflammatory mediators (7). This inflammatory process is accompanied by thrombotic events, including pulmonary thromboembolism (PTE), in COVID-19 patients (8-10).
Pulmonary thromboembolism is a cause of mortality among COVID-19 complications. While the case fatality rate for COVID-19 ranges from 2% to 3%, the mortality rate for COVID-19 patients who develop PTE is 45.1% (11). This remarkable complication is reported in 15.3 percent of COVID-19 cases (12). Due to the high mortality and incidence of PTE, as well as the fact that prompt treatment is highly effective and has been shown to significantly impact clinical outcomes, early diagnosis of PTE is crucial (12, 13).
Nevertheless, PTE diagnosis in COVID-19 is challenging for a variety of reasons. First, PTE and COVID-19 clinical manifestations may overlap (14). Second, hospital overcrowding during the resurgence of the COVID-19 epidemic, costs, and lack of availability in all centers make chest CT angiography inaccessible for all patients with probable PTE (15). Third, available clinical prediction models for PTE do not apply to COVID-19 patients. Therefore, their use as the sole diagnostic screening tool in clinical practice is not recommended. New clinical probability models for PTE that have been validated in COVID-19 patients are consequently required (16).
As previously stated, thrombotic events accompany the inflammatory process in patients with COVID-19 (8-10). Notably, hematological ratios are one of the valuable, inexpensive, and widely-examined markers of inflammation (17). In addition, circulating biomarkers of inflammation, such as Neutrophil-to-Lymphocyte ratio (NLR) and Platelet-to-Lymphocyte ratio (PLR), have been proposed as reliable prognosticators for both COVID-19 and PTE patients (18-20). Despite the importance of the aforementioned hematologic markers, there are very few studies focusing on the prediction of PTE occurrence or PTE severity in COVID-19 patients with probable PTE, accordingly, we conducted an exploratory analysis to evaluate the potential role of these parameters as predictors of thromboembolism in COVID-19 patients and the correlation of CBC parameters with the simplified-PESI score as an indicator of PTE severity.
METHOD