Healthy Group  Inclusion Criteria:  Not to have any known disease Not to use any drugs Not to have any history of chronic disease and infection Not to have any infectious symptoms To give informed consent.  Exclusion Criteria:  To have any known disease To use any drugs Moderate Disease Group  Inclusion Criteria:  To have confirmed COVID-19 infection To have positive RT-PCR in ED according to WHO guidelines To give informed consent.  Exclusion Criteria:  To have any heart, kidney or liver failure To have acute pulmonary embolism To have deep venous thrombosis or chronic inflammatory disease To have pregnancy  Severe/Critical Disease Group  Inclusion Criteria:  To have confirmed severe/critical COVID-19 infection To have positive RT-PCR in ED according to WHO guidelines To give informed consent.  Exclusion Criteria:  To have any heart, kidney or liver failure To have acute pulmonary embolism To have deep venous thrombosis or chronic inflammatory disease To have pregnancy