1. Clinic of Endocrinology, Department of Internal Medicine, Faculty of Medicine, University Hospital Alexandrovska, Medical University – Sofia, Sofia, Bulgaria;
2. Laboratory of Clinical Immunology, Department of Clinical Immunology, Faculty of Medicine, University Hospital St. Ivan Rilski, Medical University – Sofia, Sofia, Bulgaria;
3. Central Clinical Laboratory, Department of Clinical Laboratory, Faculty of Medicine, University Hospital Alexandrovska, Medical University – Sofia, Sofia, Bulgaria