G. Reber

Measurement of D-dimer in plasma as diagnostic aid in suspected pulmonary embolism

The potential of plasma measurement of D-dimer (DD), a specific derivative of crosslinked fibrin, for diagnosis or exclusion of pulmonary embolism was investigated in a prospective series of 171 consecutive patients who attended an emergency department with suspected pulmonary embolism. The diagnosis was made or excluded by means of a clinical decision-making process which included clinical evaluation, ventilation-perfusion (VQ) lung scan, and, as indicated, pulmonary angiography, venography, or non-invasive examination of the leg veins. Pulmonary embolism was diagnosed by this process in 55 (32%) of 170 patients with sufficient data. All but 1 of these 55 patients had a DD concentration of 500 micrograms/l or above. The sensitivity and specificity of this cutoff concentration for the presence of pulmonary embolism were 98% and 39%, respectively, which give positive and negative predictive values of 44% and 98%. Among the 115 patients (68%) who had inconclusive VQ scans, 31 were diagnosed as having pulmonary embolism. 29 of the remaining 84 patients without pulmonary embolism had DD concentrations below 500 micrograms/l, which means that further diagnostic procedures could have been avoided in a quarter of the patients with inconclusive VQ scans. The sensitivity of the plasma measurement of DD remained high even 3 and 7 days after presentation (96% and 93%). Plasma measurement of DD therefore has a definite place in the diagnostic procedure for suspected acute pulmonary embolism in attenders at emergency departments: a concentration below 500 micrograms/l rules out the diagnosis.

Biological effects of aspirin and clopidogrel in a randomized cross‐over study in 96 healthy volunteers

Summary.  Background: Some data suggest that biological ‘resistance’ to aspirin or clopidogrel may influence clinical outcome. Objective: The aim of this study was to evaluate the relationship between aspirin and clopidogrel responsiveness in healthy subjects. Methods: Ninety‐six healthy subjects were randomly assigned to receive a 1‐week course of aspirin 100 mg day−1 followed by a 1‐week course of clopidogrel (300 mg on day 1, then 75 mg day−1), or the reverse sequence, separated by a 2‐week wash‐out period. The drug effects were assessed by means of serum TxB2 assay, platelet aggregation tests, and the PFA ‐100® and Ultegra RPFA ‐Verify Now® methods. Results: Only one subject had true aspirin resistance, defined as a serum TxB2 level > 80 pg μL−1 at the end of aspirin administration and confirmed by platelet incubation with aspirin. PFA‐100® values were normal in 29% of the subjects after aspirin intake, despite a drastic reduction in TxB2 production; these subjects were considered to have aspirin pseudo‐resistance. Clopidogrel responsiveness was not related to aspirin pseudo‐resistance. Selected polymorphisms of platelet receptor genes were not associated with either aspirin or clopidogrel responsiveness. Conclusions: In healthy subjects, true aspirin resistance is rare and aspirin pseudo‐resistance is not related to clopidogrel responsiveness.

D‐dimer levels during delivery and the postpartum

Summary.  Background: D‐dimer (DD) measurement has proved to be very useful to exclude venous thromboembolism (VTE) in outpatients. However, during pregnancy, the progressive increase as well as the interindividual variations of DD means that in this instance they are of poor value to rule out VTE. Only a few studies have reported measurements of DD levels in the postpartum. Objectives: To measure DD sequentially in the puerperium in order to determine when DD levels return to values obtained in non‐pregnant women and can again be used in the exclusion of VTE. Patients and methods: After uncomplicated pregnancies, 150 women delivering at term either vaginally (n = 100) or by cesarean section (n = 50) were included. DD levels were measured immediately following delivery and next at days 1, 3, 10, 30 and 45. Results: There was a marked elevation of DD at delivery, especially when instrumental. All DD measurements were above 500 ng mL−1 at delivery, at day 1 and at day 3 postpartum. A sharp decrease in DD was observed between day 1 and day 3, followed by a slight increase at day 10. At day 30 and day 45, respectively, 79% and 93% of women in the vaginal delivery group and 70% and 83% in the cesarean group had levels below 500 ng mL−1. Bleeding, breastfeeding and heparin prophylaxis did not modify DD levels significantly. Conclusion: Using the Vidas DD new assay, our study provides reference intervals for DD in the postpartum period. Using a cut‐off at 500 ng mL−1, DD measurement for ruling out VTE was found to be useful again 4 weeks after delivery.

Prevalence of factor V Leiden and prothrombin G20210A mutations in unselected patients with venous thromboembolism.

We determined the prevalence of factor V Leiden and of prothrombin G20210A mutations in a cohort of unselected outpatients (n = 748) referred for suspected deep vein thrombosis (DVT) and/or pulmonary embolism (PE) and a pooled analysis of similar studies was also performed. Based on the clinical presentation, the prevalence of factor V Leiden was 15·7% in the 83 patients with DVT and 14·1% in the 99 patients with PE compared with 5·3% in patients without DVT and/or PE (control group). The prevalence of the prothrombin G20210A mutation did not differ among the three groups (3·9% for controls, 4·8% for DVT and 3·9% for PE patients). We then divided the 99 patients with PE by separately analysing those with PE but without DVT (n = 57) and those with PE and DVT (n = 42). Compared with the control group, the prevalence of factor V Leiden was 10·5%, odds ratio (OR) 2·10 [95% confidence interval (95% CI) 0·68–5·45] in patients with primary PE and 19·1%, OR 4·20 (95% CI 1·54–10·30) in patients with DVT and PE. For the prothrombin G20210A mutation, no statistically significant differences were found between the control group and the three other groups. In conclusion, our data and the pooled analysis indicate that patients with primary PE are less often affected by the factor V Leiden mutation. No statistically significant differences were observed between patients and controls for the prothrombin G20210A mutation.

Not all statins interfere with clopidogrel during antiplatelet therapy

Background Clopidogrel and statins are frequently coadministered in patients with ischemic heart diseases. Recent reports suggested that clopidogrels effectiveness in inhibiting adenosine diphosphate (ADP)‐induced platelets aggregation is attenuated by co‐administration of certain statins. The objective of the present study was to define which statin might interfere with the antiaggregation property of clopidogrel.

Effects of statins on adhesion molecule expression in endothelial cells

Summary.  Background: Inhibitors of HMG‐CoA reductase are widely used to prevent atherosclerosis progression. The expression of adhesion molecules on activated endothelial cells (EC) is an important step in the initiation and progression of atherosclerosis. Objectives: We investigated whether adhesion molecule expression on activated EC is influenced by simvastatin, fluvastatin and pravastatin and, if so, by which mechanisms. Methods: Human EC from umbilical veins or saphenous veins were pretreated overnight with statins with or without mevalonate, and also for simvastatin or fluvastatin with the isoprenoid intermediates, farnesyl pyrophosphate (FPP), or geranylgeranyl pyrophosphate (GGPP). After 4–6 h activation with tumor necrosis factor (TNF)‐α or lipopolysaccharide (LPS), surface adhesion molecule expression was evaluated by ELISA and by flow cytometry. The same experiments were performed with selective inhibitors of geranylgeranyltransferase (GGTI‐286) and farnesyltransferase (FTI‐277). Results: Pretreatment with simvastatin, fluvastatin or pravastatin potentiated the TNF‐α and LPS‐induced expression of E‐selectin and VCAM‐1, and mevalonate reversed the potentiating effect of these statins. GGPP also reversed the potentiating effect of simvastatin or fluvastatin on adhesion molecule expression, while FPP only partially reversed this effect. Furthermore, GGTI‐286, but not FTI‐277, mimicked the effect of simvastatin by increasing the TNF‐α‐mediated overexpression of E‐selectin. Conclusions: Statins increase E‐selectin‐ and VCAM‐1‐induced expression on vascular endothelial cells stimulated with TNF‐α or LPS. The inhibition of geranylgeranylated proteins could contribute to this effect.

Aspirin inhibits endothelial cell activation induced by antiphospholipid antibodies

Summary.  Background : Antiphospholipid antibodies (APLA) have been shown to activate endothelial cells (EC) in vitro, as documented by an increased expression of tissue factor as well as leukocyte adhesion molecules such as intercellular adhesion molecule‐1, vascular cell adhesion molecule (VCAM)‐1 and E‐selectin. Currently, treatment of patients with the antiphospholipid syndrome includes aspirin, particularly for women with recurrent fetal loss.

Determination of anti-cardiolipin and other antibodies in HIV-1-infected patients

Anti-cardiolipin antibodies (ACA) were determined by an ELISA assay in 116 HIV-1-infected patients. A positive test was found in 27 patients (23.3%) with a predominance of IgG ACA isotype. No significant difference in ACA positivity was observed between homosexuals (22.2%) and intravenous drug users (25.8%). The presence of different immunological markers was compared in ACA-positive and ACA-negative patients: ACA-positive patients had higher IgG levels (p < 0.05) and a tendency to higher frequencies of anti-ss DNA, anti-ds DNA, anti-i antibodies, as well as circulating immune complexes. When patients were classified according to CDC criteria, no significant difference was observed for the prevalence of ACA in class II (21.2%), in class III (25%), and in class IV (21%). Our results indicate that ACA antibodies occur with other immunological alterations in HIV-1-infected patients, but do not confirm that ACA is a useful prognostic marker for development of AIDS.

Comparison of two hemodialysis membranes, polyacrylonitrile and cellulose acetate, on complement and coagulation systems

Two hemodialysis membranes, polyacrilonitrile (AN 69) and cellulose acetate (CA), were compared for their effects on complement and hemostasis. Two groups of 5 patients, in dialysis for more than 5 years, were successively dialysed for 4 weeks periods with each type of membrane. We measured C3a (complement activation), platelets and beta-thromboglobulin (platelet activation), thrombin-antithrombin III complexes and fibrinopeptide A (coagulation activation), using C-Reactive Protein as a control for dilution effects. As previously shown, activation of complement was more important with CA than with AN 69 (p < 0.01). In contrast, activation of coagulation (increase in fibrinopeptide A and thrombin-antithrombin III complexes) was more pronounced with AN 69 than with CA. This study emphasizes the need to consider different biological systems when the bioincompatibility of a hemodialysis membrane is evaluated

A new, semi-quantitative and individual ELISA for rapid measurement of plasma D-dimer in patients suspected of pulmonary embolism.

The performance of a new membrane ELISA for semi-quantitative determination of plasma D-dimer has been evaluated. Its cut-off is about 500 ng/ml FEU and this single test is completed within 10 min. D-dimer was measured in 301 patients suspected of pulmonary embolism by conventional microplate and membrane ELISA. For the latter, readings were made by eye and some differences were noticed between the readers for reactions in the grey zone. Sensitivity and negative predictive values were similar for the two ELISA (higher than 90%). The 95% confidence intervals of sensitivity and negative predictive values obtained with this membrane ELISA suggest that this new test may be used as a diagnostic tool to exclude the presence of pulmonary embolism.