SummaryThe in vitro closure time (CT), determined by the Platelet Function Analyzer (PFA-100 TM ), is used to monitor patients treated with aspirin. A relatively high percentage of in vitro aspirin resistance was reported despite an adequate inhibition of platelet response to arachidonic acid and we investigated whether high plasma levels of von Willebrand factor ristocetin cofactor activity (vWF:RCo) may contribute to this profile. Platelet aggregation test, CT [collagen adrenaline (CEPI-CT) and collagen adenosine 5¢-diphosphate (ADP) (CADP-CT)], and vWF:RCo levels were evaluated in 55 consecutive patients receiving aspirin (75-250 mg/d) versus 32 untreated control subjects. All the aspirin-treated patients showed platelet aggregation responses that reflected the aspirin intake. However, CT data analysis enabled aspirin good-responder (GR) and aspirin bad-responder (BR) patients to be identified. All GR group subjects (n ¼ 27), had a CEPI-CT and a CADP-CT longer than 300 s and 96 s respectively. The BR group (n ¼ 28) had CEPI-CT values below 200 s and all CADP-CT were in the normal range (77 ± 19 s). Interestingly, the BR plasma vWF:RCo levels were significantly higher (159 ± 43%) than those of the GR group (121 ± 34%) (P < 0AE01), which were similar to control values (114 ± 31%). A negative correlation between vWF:RCo and CT values was established. We demonstrate that in vitro aspirin-resistance, revealed by PFA-100 TM CT prolongation failure, is correlated to increased plasmatic vWF:RCo levels, reinforcing its particular importance in PFA-100 TM cartridges performance.

These encouraging results may allow us to reduce the prophylactic PLT transfusion according to patients RP% increase.

mbH (Stuttgart) 74 (5) 1379-87 (1995) investigators suggested that coagulometer effects on INR may be corrected by using lyophilized plasma calibrants (7). Most authors agree that calibration of APTT methods should be per formed with ex vivo heparin samples, i.e. plasma samples from patients treated with heparin (2, 3, 4). It is not known whether lyophilized samples from heparin-treated patients can replace fresh samples for reliable calibration of APTT methods. The spread of individual patients' samples about the average line of relationship between different assay systems is considerable (8). The spread may be reduced or eliminated if pooled patients' samples are used to establish the average line of relationship between different APTT systems and/or more specific heparin assays. We suggest that future multicentric studies should include common deep-frozen pooled ex vivo samples in addition to fresh and lyophilized samples. Although deep-frozen samples require special conditions of transportation, they are more similar to fresh samples than lyophilized samples. Shipment of deep-frozen plasma samples to 131 laboratories was performed successfully in the Scandinavian external quality assessment scheme on coagulation (personal communication by Dr.

Both inhibition and enhancement of platelet aggregation have been observed after exposure to streptokinase (SK) in vitro. Recently we have shown that inhibition of aggregation appears to be related to the fraction containing the fibrinogen degradation product, fragment E. In addition, SK may initiate platelet aggregation by a mechanism involving specific anti-SK antibodies and plasminogen. Two monoclonal antibodies (MoAbs) (PL2-49 and LeoA1) were used to assess the immunological activation of platelets in SK-induced platelet aggregation and in SK-enhanced ADP-induced platelet aggregation. The anti-SK titers in healthy volunteers' and patients' (previously treated with SK for acute myocardial infarction) plasma, were measured using a one-site non-competitive ELISA. Serum from patients was used for the purification of IgG anti-SK by affinity chromatography. We confirmed that the degree of fibrinogen degradation is a major determinant of the aggregation inhibition induced by SK. SK-induced platelet aggregation and SK-enhanced ADP-induced platelet aggregation require the interaction of the Fc domain of the anti-SK antibodies with the FcyRII located on the platelet membrane, since they are blocked by the MoAb IV-3 directed against FcyRII. Classification of the subjects according to their responses to specific MoAbs (PL2-49 and LeoA1) supports the essential role played by immunological activation of platelets in SK-induced platelet aggregation and in SK-enhanced ADP-induced platelet aggregation. The ability of anti-SK antibodies to promote SK-induced platelet aggregation and SK-enhanced ADP-induced platelet aggregation, seems to result from the interaction between two separate mechanisms: the fist mechanism is based on immunological activation of platelets and the second is related to the intervention of a defined subset of anti-SK antibodies.