(1) D-dimer
As a degradation product of cross-linked fibrin, D-dimer is a common indicator reflecting coagulation activation and secondary hyperfibrinolysis. In patients with COVID-19, elevated D-dimer levels are an important marker for possible coagulation disorders. D-dimer levels are also closely related to disease severity, and patients with significantly elevated D-dimer on admission have a worse prognosis. Guidelines from the International Society of Thrombosis and Hemostasis (ISTH) recommend that a markedly elevated D-dimer (generally more than 3 or 4 times the upper limit of normal) can be an indication for hospitalization in COVID-19 patients, after exclusion of contraindications Anticoagulation with prophylactic doses of low-molecular-weight heparin should be given to such patients as soon as possible. When D-dimer is progressively elevated and there is a high suspicion of venous thrombosis or microvascular embolism, anticoagulation with therapeutic doses of heparin should be considered.

Although elevated D-dimer may also suggest hyperfibrinolysis, bleeding propensity in COVID-19 patients with markedly elevated D-dimer is uncommon unless progressing to the overt DIC hypocoagulable phase, suggesting that COVID-19 The fibrinolytic system of -19 is still mainly inhibited. Another fibrin-related marker, that is, the change trend of FDP level and D-dimer level was basically the same.

 

(2) PT
Prolonged PT is also an indicator of possible coagulation disorders in COVID-19 patients and has been shown to be associated with poor prognosis. In the early stage of coagulation disorder in COVID-19, patients with PT are usually normal or mildly abnormal, and the prolonged PT in the hypercoagulable period usually indicates the activation and consumption of exogenous coagulation factors, as well as the slowdown of fibrin polymerization, so it is also a preventive anticoagulation. one of the indications. However, when PT is further prolonged significantly, especially when the patient has bleeding manifestations, it indicates that the coagulation disorder has entered the low coagulation stage, or the patient is complicated by liver insufficiency, vitamin K deficiency, anticoagulant overdose, etc., and plasma transfusion should be considered. Alternative treatment. Another coagulation screening item, activated partial thromboplastin time (APTT), is mostly maintained at a normal level during the hypercoagulable phase of coagulation disorders, which may be attributed to the increased reactivity of factor VIII in the inflammatory state.

 

(3) Platelet count and function test
Although activation of coagulation can lead to decreased platelet consumption, decreased platelet counts are uncommon in COVID-19 patients, which may be related to increased release of thrombopoietin, IL-6, cytokines that promote platelet reactivity in inflammatory states Therefore, the absolute value of platelet count is not a sensitive indicator reflecting coagulation disorders in COVID-19, and it may be more valuable to pay attention to its changes. In addition, decreased platelet count is significantly associated with poor prognosis and is also one of the indications for prophylactic anticoagulation. However, when the count is significantly reduced (eg, <50×109/L), and the patient has bleeding manifestations, platelet component transfusion should be considered.

Similar to the results of previous studies in patients with sepsis, in vitro platelet function tests in COVID-19 patients with coagulation disorders usually yield low results, but the actual platelets in patients are often activated, which may be attributable to lower activity. High platelets are first utilized and consumed by the coagulation process, and the relative activity of platelets in the collected circulation is low.

 

(4) FIB
As an acute phase reaction protein, patients with COVID-19 often have elevated levels of FIB in the acute phase of infection, which is not only related to the severity of inflammation, but significantly elevated FIB itself is also a risk factor for thrombosis, so it can be used as a COVID-19 One of the indications for anticoagulation in patients. However, when the patient has a progressive decrease in FIB, it may indicate that the coagulation disorder has progressed to the hypocoagulable stage, or the patient has severe hepatic insufficiency, which mostly occurs in the late stage of the disease, when FIB<1.5 g/L and accompanied by bleeding , FIB infusion should be considered.