Ever since the report of the very first case of coronavirus disease 2019 (COVID-19) in Wuhan back in December 2019, increasing evidence indicates that COVID-19 is associated with a high thrombotic risk.^1,2 While the underlying mechanism of thrombus formation among COVID-19 patients had been well-investigated, the prevalence of detectable thrombus and its associated complications are yet to be fully explored and understood.³ In view of the missing data, a study was conducted in critically ill, COVID-19-infected patients who were hospitalized in the intensive care unit (ICU).³ In this study, a high prevalence of thrombotic complications was observed despite many patients were anticoagulated beforehand.³ To minimize the risk of thrombosis-associated death, a more proactive systematic screening of possible underlying thrombosis is thus recommended.³

COVID-19 is characterized by a myriad of clinical manifestations, which can progress from an initial asymptomatic state to subsequent multi-organ failure and death.⁴ While being regarded primarily as a respiratory illness, mounting evidence also suggests that COVID-19 can give rise to a hypercoagulable state attributable to pulmonary injury and inflammation that can lead to arterial and venous thrombosis.^4,5 Though the possible underlying pathophysiology of COVID-19-induced thrombosis and its complications were proposed in literature, other areas such as the prevalence of thrombotic complications remain understudied.³

In this regard, a single-center, retrospective analytical study was conducted in 72 critically ill patients admitted to the ICU who had COVID-19-associated acute respiratory distress syndrome, with or without extracorporeal membrane oxygenation.³ Recruited patients underwent computed tomography (CT) angiography of the thorax, abdomen and pelvis, as well as other clinically indicated imaging as per the routine institution protocols at the study hospital.³ The primary endpoint was the detection of any venous or arterial thrombus or associated complications such as deep vein thrombosis, pulmonary embolism or cerebral ischemic attack.³ The relationship between the thrombotic complications and coagulation parameters, biomarkers and survival was also evaluated.³

Out of the 72 patients, only one patient did not receive prior thromboprophylaxis or therapeutic anticoagulation.³ 54 thrombotic complications were identified in 42 patients (58%), which consisted of 34 pulmonary arterial (47%), 15 peripheral venous (21%) and 5 (7%) systemic arterial thromboses/end-organ embolic complications.³ Among the patients with pulmonary arterial thromboses, only a minority (7%) were clinically suspected with the remaining cases (93%) being identified incidentally through CT screening.³

When assessing the role of biomarkers in thrombotic complications, neither the coagulation biomarkers (D-dimer, fibrinogen level and activated partial thromboplastin time) nor the inflammation biomarkers (white blood cell count and C-reactive protein) could significantly predict thrombotic complications (p≥0.05).³

Regarding survival, 33% of patients positive for thrombotic events died versus only 10% among those who were negative for any thrombotic events.³ Therefore, patients with detectable thrombus were associated with significant mortality risk (p=0.022).³

Given that the strong association between thrombotic complications, in particular pulmonary arterial events and mortality among the critically ill, ICU-admitted COVID-19 patients in spite of prior thromboprophylaxis, the investigators recommended clinicians to better utilize systematic CT imaging to reveal potential thrombosis earlier and accurately to minimize the risk of complications and deaths, instead of solely relying on clinical features to help identify any thromboembolic disease.³

While the study was limited by its 3-month study duration and ICU setting, it has nonetheless emphasized the high prevalence of thrombotic risk among specific groups of COVID-19 patients and highlighted the importance of proactive systematic screening among these patients. With earlier diagnosis and intervention, these at-risk COVID-19 patients may have a better chance of complication-free survival.