1. Department of Internal Medicine (Rheumatology and Clinical Immunology), University Hospital Charité, Humboldt‐University, Berlin, Germany,
2. Outpatients Department, University Hospital Charité, Humboldt‐University, Berlin, Germany,
3. Fresenius AG, St. Wendel, Germany,
4. Imtec Immundiagnostika, Berlin‐Buch, Germany