1. University Hospital “Sv. Ivan Rilski” Medical University, Bg – 1431 Sofia, Bulgaria
2. Department of Clinical Laboratory and Clinical Immunology, Alexandrovska University Hospital, Medical University – Sofia, Bulgaria
3. Clinic of nephrology, Sv. Ivan Rilski University Hospital, Medical University – Sofia, Bulgaria
4. Central Clinical Laboratory, Sv. Marina University Hospital – Varna, Medical University – Varna, Bulgaria