Our study aimed to demonstrate with clinical, radiological and haemostasis markers the possibility to predict clinical worsening in Covid-19 patients and to determine the best thrombotic event predictor.
Since December 2019, several clinical and biological markers were associated with poor prognosis in Covid-19 patients. Elderly, increase body mass index, hypertension (28), diabetes and male gender (29) were regularly associated with mortality. Our study only confirmed elderly as a potential predictor under unadjusted hypothesis and a trend for gender, HTA and diabetes that could be due to our limited sample size (99 patients of which 35 worsening). As expected, oxygen therapy in preadmission was a predictive factor to develop worsening SARS-CoV-19. Chest computed tomography examination is recommended for the detection of lesions, early diagnosis, and assessment of the disease extension (19). Interestingly in CT scan, pulmonary disease extension >25 % was associated with a rapid progression of Covid-19 pneumonia and worsening in our patients.
Lymphopenia is a prominent part of severe Covid-19. A meta-analysis described lymphopenia<1.5 G/L predicting the severity clinical outcomes (30), however lymphopenia is defined as under 1 G/L in our laboratory and more than 78% of our cohort exhibited lymphocytes level below 1.5 G/L (56% below 1G/L). Interestingly, our results suggest a non- significant relationship between lymphopenia and SARS-CoV-2 severity. To our knowledge, we first describe that monocytopenia below 0.2 G/L could be related to Covid-19 severity. This is in accordance with the fact that a decrease monocyte count is associated with poor prognosis in sepsis (31). Recruitment of monocytes is essential for effective control and clearance of viral, bacterial, fungal and protozoal infections (32) . The inflammatory recruitment failure is also possible explanation to aggravation.
Yan et al. reported a correlation between neutrophil to lymphocyte ratio at hospital admission and all-cause in-hospital mortality (33). In our cohort, neutrophil to lymphocyte ratio was not associated with intensive care unit hospitalization and death. Interestingly, the fact that neutrophil to monocyte ratio was increased in worsening patients could be explained by a reduced monocyte count.
It has been previously demonstrated that fibrinogen and D-dimer were whereas antithrombin was normal or mildly decreased in worsening patients compared with clinical improving (34-36). In the review, published by Violi et al. (37), it was resumed that D-dimer, PT and aPTT were often compared between survivors and non-survivors or severe and non- severe patients. In all cases, D-dimer level was significantly higher in severe or non survivors patients than in non-severe or survivors patients respectively. Our results suggest that fibrinogen<5.5 g/L was associated with a better outcome in our patients, with a high discriminate power and in a more specific manner than D-dimer does.
Several studies have described DIC in some Covid-19 patients. In the study of Fogarty et al. (38), DIC was rare and appeared in the late stage disease. In two others studies (8, 39) DIC was significantly more frequent in non survivors than in survivors. In contrast in the 24 patients from Panigada’s report (34) DIC was not evidenced. With International Society Thrombosis and Haemostasis score, we demonstrated DIC score increase with D-dimer, in worsening patients with more than 75% with a DIC score below of 3. With fibrin monomer, more than 75% worsening patients had a DIC score below of 1. Furthermore, the increase of platelet and fibrinogen, associated with normal prothrombin time in our patients explain normal DIC score results.
Interestingly, our results demonstrated that the association of fibrinogen level, thrombin peak measurement and oxygen dependency was an easy-to-apply model that could predict near than 80% of clinical outcome. Of note, we observed 33/35 patients with oxygenodependence in clinical worsening group among which 26 had fibrinogen level higher than 5.5 g/L and TGA peak higher than 99 nM suggesting the ability of these last two parameters to predict clinical outcome.
In the Study of Panigada et al. (34), von Willebrand factor antigen and ristocetin cofactor activities were very increased. In Poissy et al. study (40), factor Willebrand antigen levels seem to be associated with a greater PE risk. Our study demonstrated an increase in von Willebrand factor activity in patient whose worsening. However, VWF:GPIb-binding activity was not the most predictive factor of thrombotic development during hospitalization, the AUC sensibility and specificity being 76.0%, 75.0% and 75.8% respectively, with a threshold 305 %.
In the literature, up until now, there was no description of thrombin generation profile in Covid-19 patients. Three studies looked at procoagulant profile thanks to thromboelastography (34, 36) or viscoelastic tests (35). In these studies, hypercoagulant profile was demonstrated in patients with acute respiratory distress syndrome (ARDS) or admitted to ICU. TGA has already been used to evaluate hypercoagulability (41) and acute ischemic stroke development (42). The fact that SARS-CoV-2 virus induces severe endothelial injury associated with intracellular virus and disrupted endothelial cell membranes (43) make TGA an interesting tool to predict clinical outcome of SARS-CoV 2 infected patients since microangiopathy and occlusion of alveolar capillaries from lung patients with Covid-19 were founded to be secondary to widespread vascular thrombosis (43). Interestingly, the global thrombin formation, reflected by ETP, is not increase (990 nM.min [718-1237] vs 1132 nM.min [905-1465] for improving and worsening patient respectively) but we observed an increase in peak and velocity in clinically worsening patients. Activated coagulation is an expected response to the inflammatory through several procoagulant pathways. Usually, thrombin generation participate to host response, but when exaggerated, it is associated with thrombosis. The endothelium supports an extensive repertoire of natural anticoagulant. However during sepsis, activated endothelium increase TF expression within the vasculature is considered a pivotal step in initiating and sustaining coagulation. The concept of thrombosis associated with inflammation is known as thromboinflammation (44). Overall, the results of TGA support the concept that the hypercoagulability is associated with endothelial dysfunction, due to the profound activation and amplification of coagulation.
According to many reports, Covid-19 exposes patients to a particularly high risk for venous thromboembolism (45, 46). The prevalence of pulmonary embolism in the ICU is near 20% (40). ISTH and the American Society of Hematology recommended prophylactic dose of low molecular weight heparin to prevent thrombotic event (47-49). Even with thromboprophylaxis, 7.7% of patients in academic hospital of Milan developed thrombotic event (50). The association between Padua score>4 and D-dimer>1000 µg/L had a sensitivity of 88.52% and a specificity of 61.43% for screening risk for DVT (51). In our study, the AUC sensibility and specificity being 77.5%, 75.0% and 89.0% respectively, with a threshold 2555 µg/L. No study was reported about prothrombin fragments 1+2 in Covid-19. Prothrombin fragments 1+2 are less impacted by inflammation than D-dimer (52). In our study on admission, thrombin peak was extremely specific (with 100%) and prothrombin fragment 1+2 was sensitive to predict PE. The association between different haematological markers could help to predict, and potentially, increase anticoagulation thromboprophylaxis. Our results supported a possible worsening and PE prediction with prothrombin fragments 1+2, even with a small number of cases.
Nevertheless, our study presents several limitations. First, we have a low number of included patients. However, our objectives (clinicaltrials: NCT04367662) were to determine a rapid method to help clinician for patient discharged. Despite our 99 patients, we have a robust algorithm to predict worsening. Second, we had a low number of thrombotic events. However, the rate was in accordance with other studies with patient who developed a pulmonary embolism.