1. Department of Clinical Biochemistry, Harrogate District Foundation Trust, Lancaster Park Road, Harrogate, HG2 7SX, UK
2. Bio-Rad Laboratories, Quality System Division, Plano, Fairview , TX , United States of America
3. Dutch Foundations for Quality Assessment in Clinical Laboratories (SKML) , Nijmegen , The Netherlands
4. WEQAS Quality Laboratory, Cardiff and Vale University Health Board, Cardiff, UK
5. Blood Sciences, Old Medical School, Leeds Teaching Hospitals Trust, Leeds, UK