Persons who have had a coronavirus infection long after recovery experience symptoms such as hair loss, micro-strokes, recent onset of diabetes mellitus, long-term fatigue, muscle pain, depression, sleep disturbance and many others. Because of this, there is no clear picture of what constitutes Post-COVID-19 syndrome. Without a formally accepted definition of post-coital syndrome, it is difficult to assess how common it is, how long it lasts, and who is at risk. Several studies are being initiated to define this group of patients.

• Clinical blood count with white blood cell count (СBC) is a basic laboratory test that evaluates the cell count, shape, size, and ratio of the fortified elements. This simple and informative test provides a comprehensive assessment of the state of health, allows timely diagnosis of pathologies, including latent ones. Сomplete blood count reveals infectious, haematological, allergic, oncological processes occurring in the body, reflects the dynamics of diseases and the effectiveness of therapy, reveals the toxic effects of drugs. D-dimer is the result of fibrin breakdown during the dissolution of blood clots (fibrinolysis).
• D-dimer analysis allows to evaluate 2 factors at once: coagulation (blood clotting) and fibrinolysis (dissolution of clots). The marker enables timely detection of imbalance between them in case of diseases of the circulatory system (varicose veins, thrombophilia, pulmonary embolism, etc.).
• C-reactive protein is a protein produced by the liver and is one of the marker proteins of inflammation. Protein levels increase with inflammation, so it is now considered a key biomarker of systemic inflammation. It plays an important role in defence against infection. CRP binds to the cell surface of many pathogenic microbes, thus activating the immune system. Bilirubin total and direct - shows the work of the liver, the rate of destruction of red blood cells and the presence of bile stasis. It consists of two parts - direct, neutralised by liver cells, and indirect, dangerous for the body.
• Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) are enzymes that are found in all cells of the body and are responsible for catalysing and interconverting amino acids. ALT is mainly concentrated in the liver and AST in muscle tissue. Elevated levels of ALT and AST indicate liver damage of various etiologies. For example - alcohol, medication or any other toxic damage; cirrhosis (before coma); acute viral hepatitis (hepatitis A, B, C, E, F, herpes viruses) or chronic viral hepatitis B or C, with or without delta agents; autoimmune hepatitis, excessive physical exertion, infancy. Also, mechanical or ischaemic tissue damage, severe burns; heat stroke, myocarditis, myositis, intestinal obstruction; acute pancreatitis, obesity, ischaemic stroke, haemophilia.
• Glucose (blood sugar) – plays an essential role in providing energy to body tissues and in cellular respiration. If glucose levels are outside the normal range, cellular energy starvation occurs. If glucose is chronically low in a person, brain and nerve cell damage can occur. A major marker of diabetes mellitus and diabetes-related complications.
• Creatinine in the blood is a product of protein breakdown. It is formed in the muscles and then enters the bloodstream, filtered by the kidneys and excreted in the urine. Creatinine is necessary for energy metabolism in body tissues. The more muscular work, the more creatinine is excreted as it is an energy product.  
• Urea is the end product of protein metabolism. It is produced in the liver, transported by the blood to the kidneys, filtered through the vascular bed and then excreted. The result of the test shows the kidney function.