Hemostatic system and COVID-19 crosstalk: A review of the available evidence

Table 1 The various hematological parameters in significant relation to coronavirus disease 2019 and their mechanisms

Hematological parameter	Significant relation to COVID-19	Mechanism
High RDW (greater than 14.5%)	Increase in mortality risk (from 11% to 31%)[86]	Not completely understood however reports suggested elevated RDW was attributed to affection of RBC production kinetics[86]
Leucopenia or lymphopenia (ALC < 1.0 × 109/L)	Observed in most of COVID cases especially hospitalized patients and associated with poor prognosis[86]	(1) Defective immune response; and (2) Drug induced as with steroids[87]
Normal or increased platelet count	Found in some cases of COVID-19	May be caused by to the large amounts of platelets produced in response to increased thrombopoietin formation from liver stimulation and megakaryocytes in the lung[88]
Prolonged PT and aPTT, elevations of D dimer, fibrinogen and FDP and decreased levels of antithrombin III	Direct relationship was observed between severity of COVID and affection of coagulation profile, Overt DIC (ISTH score of 5 and higher) is seen more frequently in non-survivors[89]	aPTT prolongation is caused by increased Factor VIII level and Factor XII deficiency secondary to the presence of factor XII inhibitors. Von Willebrand factor is quantitatively increased. LA is positive in 91% of those with prolonged aPTT. The presence of both LA and Factor XII deficiency are not associated with bleeding tendency

ALC: Absolute lymphocyte count; aPTT: Activated partial thromboplastin time; COVID-19: Coronavirus disease 2019; DIC: disseminated intravascular coagulation; ISTH: International Society on Thrombosis and Hemostasis; LA: Lupus anticoagulant; PT: Prothrombin time; RBC: Red blood cell; RDW: Red cell distribution width.