We have evaluated the performance of a new analyzer using high shear stress, the PFA-100 (Platelet Function Analyzer, Dade International, Massy, France), for screening of patients with von Willebrand disease (vWD). Whole citrated blood is aspirated through a capillary to the central aperture of a membrane coated with collagen and with a platelet agonist (either epinephrine or adenosine diphosphate [ADP]). The time required to obtain occlusion of the aperture by a platelet plug is defined as the closure time (CT). We studied 60 patients with different types of vWD and 96 normal subjects. Fourteen subjects with hemophilia and 15 patients with a platelet disorder were also analyzed. When omitting results from two patients with type 2N, the 58 other patients with type 1, type 2A, type 2B, type 3, or acquired vWD all exhibited an abnormal occlusion with collagen-ADP (sensitivity, 100%) and 56 of 58 had an abnormal CT with collagen-epinephrine (sensitivity, 96.5%). Only two patients with mild type 1 were not detected with collagen-epinephrine. In comparison, the bleeding time (BT) was normal in 20 patients: 17 with type 1, two with type 2A, and one with acquired vWD (sensitivity, 65.5%). The specificity of the PFA-100 was over 95% with both types of cartridges. Thus, the analyzer is well adapted to routine testing, as it has the advantages of simplicity and ease of execution, and demonstrates a high sensitivity, clearly superior to that of BT, for the screening of patients with vWD.

SummaryAs heparin-PF4 (H-PF4) complexes are the target for antibodies associated to heparin-induced thrombocytopenia (HIT), an ELISA has been developed and optimised for testing antibodies binding to H-PF4. This test was consistently negative in 50 healthy subjects (A492 <0.3) and 35 patients with other causes of thrombocytopenia (A492 <0.5). In contrast, 43 out of 44 HIT patients showed antibodies to H-PF4 (A492 = 1.70 ± 0.81) including 5 patients with a negative platelet aggregation test. In one patient with HIT, antibodies to H-PF4 were already present at day 7, whereas platelet counts dropped ≤ 100 × 109/l only at days 11–12. Surprisingly, among 41 patients under heparin for >7 days, 5 showed antibodies to H-PF4, without HIT. These findings underline the major interest of this ELISA for the early diagnosis of HIT. We also showed that LMWH as well as other sulphated polysaccharides can bind to HIT antibodies in the presence of PF4 and that their reactivity is dependent on the molecular weight and the sulphation grade. The mechanism for HIT involves platelet PF4 receptors which bind the macromolecular H-PF4 complexes formed in the presence of a well defined heparin/PF4 ratio.

Thrombotic lesions are consistently observed in chronic thromboembolic pulmonary hypertension (CTEPH) and frequently found in primary pulmonary hypertension (PPH). It remains unknown, however, whether thrombosis is related to defects of the antithrombotic pathway or to previous vascular injury. This study therefore analysed the frequency of both hereditary and acquired thrombotic risk factors in CTEPH and PPH.One hundred and forty-seven consecutive patients with CTEPH investigated in the author's institution were compared to 99 consecutive patients with PPH. In 116 CTEPH patients and 83 PPH patients, phospholipid-dependent antibodies (antiphospholipid antibodies and lupus anticoagulant) were analysed by both immunological and clotting assays. In patients enrolled since 1994 (46 CTEPH and 64 PPH), hereditary thrombotic risk factors were also determined. Antithrombin, protein C and protein S activities were measured by functional assays. Mutations of factor V and factor II were identified by polymerase chain reaction.The prevalence of hereditary thrombotic risk factors was not increased in patients with either PPH or CTEPH. In contrast, a high frequency of phospholipid-dependent antibodies was observed in PPH (10%) and more notably in CTEPH (20%). Moreover, in PPH, antibodies were present only in low titre whereas in CTEPH, half of the patients with antiphospholipid antibodies had high titres. In addition, in CTEPH all but one of the patients with lupus anticoagulant also had antiphospholipid antibodies.The most striking finding of this study was the high prevalence of phospholipiddependent antibodies but their clinical relevance appears to be different in primary pulmonary hypertension and chronic thromboembolic pulmonary hypertension. In primary pulmonary hypertension, these antibodies in low titre probably reflect endothelial dysfunction. In contrast, in chronic thromboembolic pulmonary hypertension the presence of antibodies in high titre associated with lupus anticoagulant, underlines the role of thrombosis in the pathogenesis of this condition. Eur Respir J 2000; 15: 395±399. Pulmonary hypertension (PH) is a serious condition with significant morbidity and mortality. A large spectrum of diseases are included under this rubric, roughly divided into primary pulmonary hypertension (PPH) and secondary pulmonary hypertension. The definition of PPH is based on the exclusion of secondary causes of PH viz hypoxic lung disease, congenital heart disease, chronic thromboembolic disease, and associated conditions such as collagen vascular diseases, human immunodeficiency virus (HIV) infection, portal hypertension and exogenous substances [1]. Although the pathogenesis of the increased vascular resistance in PPH remains unknown, vasoconstriction, vascular remodelling and thrombosis may all contribute. In fact clinical data and histological features of PH suggest that thrombosis may be important in the pathophysiological state of PH, especially in PPH and chronic thromboembolic pulmonary hypertension (CTEPH). Se...