The meeting was attended by 80-120 people.

This topic was first discussed by the subcommittee in 1998, since then there has been considerable progress both in functional and antigen assays. The recent work of five groups was presented, allowing a reasonable consensus to emerge. Dr. Dirk Hendriks summarised a functional assay in which all the procarboxypeptidase U (PCU) is activated, after which it can be measured by the release of hippurate by HPLC. This correlated well with a measure of total PCU by ELISA. There was a strong correlation between plasma PCU and time for t-PA-mediated plasma clot lysis. Dr. Laurant Mosnier then presented his studies, using very similar approaches, this time with released hippurate being measured colorimetrically. Dr. Anthony Chan then made a presentation on behalf of Dr. Lazslo Bajzar, whose group has developed ELISA methods, based on either polyclonal or monoclonal antibodies. The assay is sensitive to native TAFI and sees it less well after activation. They too examined the relationship between plasma TAFI and endogenous fibrinolytic activity, this time measuring euglobulin lysis time, and found no correlation. Dr. Kees Kluft presented data on TAFI, measured by ELISA, in normal individuals. The most notable findings were the wide variation in normal concentrations and correlation with markers of inflammation. Dr. Irene Juhan-Vague presented ELISA data on normal individuals and in a group of patients. Correlations were observed between TAFI and some known risk factors for cardiovascular disease. General discussion of all these findings included suggestions that both activity and antigen needs to be measured, that care should be taken to make sure that there is no interference in the assays from other plasma factors, and that the wide normal variation might reflect genetic polymorphisms. It was suggested that the speakers and any others interested should form a working group to summarise assays that are readily available, and to compare data before the meeting in Maastricht in 2000. Exchange of samples in order to compare different assays may also be possible.

Dr. Patrick Gaffney, in his final presentation before he retires, summarised the standards and reference materials that are available and discussed their use in different studies. The t-PA standard was discussed in detail by Dr. Colin Longstaff. A new standard for t-PA is now required and a collaborative study was recently completed, in which the new putative standard was compared to the existing t-PA standard. The report on this study was sent last month to a panel of members. All responses to date supported the acceptance of the new standard and several commented favourably on the study. The potency is 10000 IU based on 12 laboratories using fibrin-based assays. A minority of contributors to the study felt that the value of 10500 IU should be adopted; this was based on 14 laboratories, the additional 2 using a different assay. It should be noted that previous standard was measured only in fibrin-based assays. Both these issues, the acceptance of the new standard and the actual value, were put to a vote. There were no votes against the acceptance of the standard. The value of 10000 IU was accepted by 12 votes to 1. It was noted that there were a very large number of abstentions, especially in the second vote, most of those present not having a strong view. This t-PA preparation will now be recommended as a new standard, with a value of 10000 IU, to the WHO Expert Committee on Biological Standardisation.

Dr. Victor Gurewich reviewed the data that suggest that u-PA has a role in fibrinolysis independent of the receptor, u-PAR. This included data from animal models, including knockout mice, and from studies on human blood. His own work shows that clots of platelet-rich plasma were lysed more readily by single-chain u-PA (also called proUK) than were platelet-free clots; the opposite is true of lysis by t-PA. He concluded that physiological fibrinolysis is critically dependent on the strong binding by platelets of u-PA and encouraged others to assess its role.

This was a new topic for this subcommittee, formerly having been discussed by the fibrinogen committee. Dr. Dempfle reviewed different assays for D-Dimer and concluded that some of them are equally sensitive to soluble fibrin and D-Dimer, some of the assays being related to plasmin degradation and some not. Dr. Piet Meijer presented the ECAT experience of measurement of D-Dimer. It became clear that there was a problem of using different assays and different plasma samples in many studies, such that a solid basis for comparison is lacking. Dr. Willem Nieuwenhuizen summarised his work on measurement of D-Dimer. He had hoped to make available a set of plasma samples, suitable for comparisons between different laboratories; he now intends to provide these. This was warmly welcomed and it is intended that studies on these samples should be presented to future meetings of the subcommittee and to liaise with the fibrinogen committee.

Dr. Kees Kluft discussed the measurement of the SSC standard for proteins of the fibrinolytic system, which had been hampered by discrepancies between assays. The problems of assaying t-PA and PAI-1 have now been resolved. Dr. J Sidelaman, who last year presented data on the wide fluctuations in plasminogen measurements in a WHO EQAS initiative, reported on the conclusions of a small working party on measurement of plasminogen. It recommends the use of streptokinase activation and functional measurement, essentially as in the ECAT procedure.

It was agreed that topics for the SSC meeting in Maastricht should include

PCU / TAFI

D-Dimer

Results of current work on standards

Further suggestions should be sent to Dr. Booth (n.a.booth@aberdeen.ac.uk), Dr. Declerck, (Paul.Declerck@farm.kuleuven.ac.be), Dr. Kluft (Kluft@euronet.nl) or Dr. Matsuo (kr9o-mto@asani-net.or.jp).

The meeting finished shortly before 5 p.m.