1. Norwegian Porphyria Centre , Laboratory of Clinical Biochemistry , Haukeland University Hospital , NO-5021 Bergen , Norway , Phone: +47 55 97 31 27/ +47 55 97 31 70, Fax: +47 55 97 31 15
2. Norwegian Quality Improvement of Laboratory Examinations (Noklus), Haraldsplass Deaconess Hospital , Bergen , Norway
3. Blood Sciences, Ninewells Hospital and Medical School , Scotland , UK
4. Acibadem University, School of Medicine , Atasehir, Istanbul , Turkey
5. Servizio di Medicina di Laboratorio, Ospedale San Raffaele , Milan , Italy
6. Hospital Universitario La Paz , Madrid , Spain
7. Spanish Society of Laboratory Medicine (SEQC ) , Barcelona , Spain
8. Certe, Wilhelmina Ziekenhuis Assen , Assen , The Netherlands
9. Research Centre for Metrological Traceability in Laboratory Medicine (CIRME), University of Milan , Milan , Italy
10. Norwegian Porphyria Centre , Laboratory of Clinical Biochemistry , Haukeland University Hospital , Bergen , Norway
11. Department of Global Health and Primary Care , Faculty of Medicine and Dentistry, University of Bergen , Bergen , Norway