1. Division of Clinical Chemistry, Department of Medical Laboratory Sciences and Technology, Huddinge University Hospital C1 74, Karolinska Institutet, SE-141 86 Stockholm, Sweden, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, SE-171 77 Stockholm, Sweden, Department of Haematological Medicine, King's College Hospital, Denmark Hill, London SE5 9RS, U.K., and Micromass UK Limited, 3 Tudor Road, Altrincham, Cheshire, WA14 5RZ, U.K.