RESUMEN
An international collaborative study was organised to replace the 2nd International Standard (IS) for tissue plasminogen activator (tPA). The 2nd IS for tPA (86/670) was used to calibrate the replacement Standard, which was selected from two candidate materials included in the collaborative study. Participants were provided with five sets of four samples (A, B, C, D) and asked to use sample A (2nd IS, 86/670, 850 IU/ml) to determine the activity of B (86/624, approximately 850 IU/ml), C and D (coded duplicates of the same material, 98/714 approximately 11,000 IU/ml). A total of 14 laboratories returned results from Europe, USA, Japan and Australia, providing data from 60 independent assays. Four laboratories used a reference method based on a published monograph from the European Pharmacopoeia for Alteplase for Injection, 1998, and the remaining 10 used their own method. Fibrin was used as promoter of tPA activity by 12 out of the 14 laboratories, the remaining two used kits where fibrinogen fragments were the promoter. Data from this collaborative study and the previous study to establish the 2nd IS for tPA show that tPA from melanoma cells and recombinant tPA from CHO cells are both suitable materials as International Standards. It was agreed that sample C, D, recombinant tPA, 98/714, be established as the 3rd International Standard for tPA with a potency of 10,000 IU per ampoule, calculated as the mean value from laboratories using fibrin as a promoter of tPA activity. The standard was established by WHO in November 2000.