Apart from respiratory failure, coagulopathy is a common abnormality in patients with COVID-19.
Klok FA et al.  reported a high incidence of thrombotic complications (acute pulmonary embolism (PE), deep vein thrombosis, ischemic stroke, myocardial infarction or systemic arterial embolism) in patients with COVID-19 infections (31%) admitted at ICU. All patients received at least standard doses thromboprophylaxis.
Data about the incidence of DVT is scarce. A recent published study has shown an incidence of 25% of DVT in ICU COVID-19 patients; the significant increase of D-dimer resulted as a good index for identifying high-risk patients .
Llitjos JF et al. reported 69% incidence rate of DVT in severe mechanically ventilated COVID-19 patients; all patients were treated with therapeutic anticoagulation from admission .
Even in our Hospital, from the beginning of the outbreak, an unusually high mortality rate due to pulmonary embolism occurred among hospitalized COVID-19 patients who were under prophylactic dose of low molecular weight heparin. Therefore, we decided to implement a screening program for DVT in COVID-19 patients hospitalized.
We found that DVT even occurs in patients treated with therapeutic anticoagulation from admission, highlighting the high thromboembolic potential of COVID19. Bedrest and ICU admission resulted significantly associated with the presence of DVT.
Our results have shown an incidence for DVT of 10.7%, lower than in other mentioned publications. The reason is to be found in the fact that our study is the only one in which even patients less severely affected from low intensity wards were included. In medicine wards we found only 1 out of 60 hospitalized patients, with an incidence of 1.6%, similar to that reported in the same wards in non-COVID-19 patients (1.3%) [1, 9, 10]. This observation led us to suppose that in less severely affected patients in low-intensity Covid-19 wards, execution of DUS as screening of DVT might be unnecessary. Our overall incidence of DVT increases to 13.8% considering mid-and high-intensity Covid-19 units (24/174).
Strengths of the present study is represented by the large analyzed series, which to date, is the largest in literature. Moreover, an association with clinical, laboratory’s and therapeutic parameters was investigated and confirmed for the first time. Indeed, both the fraction of inspired oxygen, P/F ratio and the respiratory rate and heparin administration, d-dimer, IL-6, ferritin and CRP resulted correlated with the presence of DVT.
However, the study presents some limitations, especially in its retrospective design. Moreover, DUS was performed earlier in DVT patients and DVT patients had an higher dose of heparin, so an underestimation of DVT may be suspected in some cases. This suggests that clinical and laboratory suspicion before investigation is always mandatory.
The high rate of DVT found in our severe COVID-19 patients who were under prophylactic treatment and correlation with respiratory parameters and some significant laboratory findings suggests that these can be used as a screening tool for patients who should be getting DUS . In these patients, DUS may be considered a useful and valid tool for early identification of DVT.