Introduction
In December 2019 an out break of disease caused by the virus SARS-CoV-2 was declared in China. This disease, later named Covid-19, spread throughout the world in the first few months of 2020 [1, 2]. Around 80% of patients have mild symptoms, the rest can develop severe disease, mainly interstitial pneumonia and acute respiratory distress syndrome, and require hospital admission. Intensive care may be necessary for 5% of patients. Mortality is estimated to be less than 2% [3, 4]. The large number of simultaneous cases of Covid-19 has overloaded hospitals, making it very difficult to provide an adequate care. The spread of Covid-19 is negatively affecting all areas of healthcare, and is also having an adverse impact on the entire society and the international economy.
Thrombotic events in different tissues, with consistent clinical laboratory and radiological findings, have been reported in patients with Covid-19 [5–7]. Perfusion abnormalities in lungs have been observed in patients who underwent dual-energy CTs [8]. There is also pathological evidence of the presence of platelet-fibrin thrombi in small arterial vessels in lung tissues of patients who have died of Covid-19 [9]. Based on these finding, doctors have used heparin to treat or prevent the coagulation disorder associated with the infection [5–7, 9]. This treatment can be associated with the clinical improvement of the patients, and decrease the duration of admissions and the mortality of Covid-19. Heparin is safe, economical, and easy to use, it can be given both to admitted and outpatients. However, the use of heparin in Covid-19 patients is still supported by limited evidence. This study investigates the association of the use of heparin with mortality in a large number of patients admitted with Covid-19.