1. Department of Urology, Royal Free and University College Medical School, University College London, Royal Free Campus, Rowland Hill Street, London NW3 2PF, England, and Department of Clinical Biochemistry, Royal Free and University College Medical School, University College London, Royal Free Campus, Rowland Hill Street, London NW3 2PF, England
2. Department of Urology, Chase Farm Hospital, The Ridgeway, Enfield EN2 8JL, England
3. Department of Clinical Biochemistry, Royal Free and University College Medical School, University College London, Royal Free Campus, Rowland Hill Street, London NW3 2PF, England
4. Department of Clinical Biochemistry, Royal Free Hospital, Pond Street, London NW3 2QG, England,