D. S. Korolova¹*, O. O. Shevchuk², O. P. Kostiuchenko¹,
, K. P. Klymenko¹, T. M. Platonova¹,
Ya. I. Ivankiv², S. M. Paliy², A. I. Voitovych², V. O. Chernyshenko¹,
M. M. Korda², S. V. Komisarenko¹, S. G. Vari³,

¹Palladin Institute of Biochemistry, National Academy of Sciences of Ukraine, Kyiv;
²Ivan Horbachevsky Ternopil Medical University, Ternopil, Ukraine;
³International Research and Innovation in Medicine Program, CSMC, Los-Angeles, CA, USA;
*e-mail: d.korolova@gmail.com

Received: 08 May 2026; Revised: 18 July 2026;
Accepted: 27 July 2026; Available on-line: August 2026

Background. In recent period the attention of scientists and doctors was focused mainly on methods of COVID-19 treatment. However, clinical course of coronavirus disease strongly affects blood coagulation with the tendency for venous and arterial thrombosis, leading to long-term imbalance between coagulation and anticoagulation systems, which can cause serious danger for health of post-COVID-19 (PCD) patients. Objective. In our work we focused on the analysis of the molecular markers of hemostasis system activation in blood plasma of patients recovered after COVID-19. Methods. Blood plasma samples of 119 seropositive patients recovered from COVID-19 were analysed. The patients were divided into a high-risk group (HRG, n = 163) and a non-risk group (NRG, n = 28) according to WHO recommendations. Patients were examined in a recovery time scale of 1-30; 31-60 days and more than 2 months. Blood plasma samples of seronegative healthy volunteers were collected as the reference group (n = 19). The concentration of soluble fibrin (SF) and D-dimer was measured with sandwich ELISA, generation of activated protein C (PC) and prethrombin-1 (Pre-1)) level with assay using specific chromogenic substrates, and fibrinogen concentration with spectrophotometric method after initiation of coagulation by Ancistron-H. Results. Concentration of fibrinogen, SF and Pre-1 were increased in a blood plasma of patients of NRG and HRG groups in comparison to the reference group. Increasing of fibrinogen and Pre-1 concentrations correlated with COVID-19 stage. The fibrinogen and SF concentrations remained high more than 2 months after recovery in HRG group and elevated after 2 months after recovery in NRG group. D-dimer and protein C levels were elevated in 8% and 11% of PCD patients respectively. Conclusions. Long-term prethrombotic state was more expressed in HRG group of PCD patients. Monitoring of the main coagulation markers can indicate the risk of intravascular thrombus formation in PCD patients. SF, Pre-1 and elevated fibrinogen concentrations were selected as useful thrombosis markers in PCD patients.