Effect of clot-detection methods and reagents on activated partial thromboplastin time (APTT). Implications in heparin monitoring by APTT.

Two automatic coagulometers, ACL 810 (Instrumentation Laboratory), a laser-nephelometric centrifugal analyzer, and KoaguLab 40 A (Ortho Diagnostics), an optical automatic coagulometer, were compared with the manual tilt-tube method for the performance of activated partial thromboplastin time (APTT). Seven commercial APTT reagents were used for duplicate determinations in 30 normal controls, 26 patients with liver disease, and 33 patients on full-dose heparin treatment. Clotting times were longer with the manual method than with ACL 810 and, to a lesser extent, with KoaguLab 40 A. Average imprecision of duplicate determinations (coefficient of variation [CV]) was less with ACL 810 (less than 1.5%) than with KoaguLab 40 A (2.9%) and the manual method (2.4%). Differences in slope of the regression curves of clotting times obtained with the coagulometers over the tilt-tube method were observed with all the reagents tested (P less than 0.01). Transformation of clotting times of controls, patients with liver disease, and patients on heparin therapy to APTT ratios did not eliminate the bias resulting from the different reagents (P less than 0.001) and clot-detection methods (P less than 0.001); in controls, significant (P less than 0.001) reagent-method interaction was also observed. The in vitro heparin sensitivity differed with the APTT reagents evaluated and was influenced by the clot-detection method used. Transformation of APTT ratios of anticoagulated patients to apparent plasma heparin levels--as derived from in vitro dose-response curves--effectively eliminated the bias resulting from the different clot-detection methods but had no effect on the bias resulting from the different APTT reagents. In vitro heparin activity curves thus have little, if any, relevance for the ex vivo monitoring of heparin treatment.

Comparison of two automated coagulometers and the manual tilt-tube method for the determination of prothrombin time.

Two automatic coagulometers--ACL 810 (Instrumentation Laboratory), a laser-nephelometric centrifugal analyzer, and KoaguLab 40 A (Ortho Diagnostics), an optical automatic coagulometer--were compared with the manual tilt-tube method for the performance of prothrombin time (PT). Seven ISI- (International Sensitivity Index) calibrated commercial thromboplastin reagents were used for duplicate determinations in 30 normal subjects, 30 patients with liver disease, and 30 patients receiving stabilized oral anticoagulation. Clotting times were longer with the manual method than with ACL 810 and, to a lesser extent, with KoaguLab 40 A. Average imprecision of duplicate determinations (CV) was less than 1% with ACL 810; KoaguLab 40 A and the manual method had similarly higher imprecisions (2.8% and 2.7%). Differences in origin and slope of the regression curves of clotting times obtained with the coagulometers over the tilt-tube method were observed with all the reagents tested. Transformation of clotting times to PT ratios did not eliminate the bias resulting from the different clot-detection methods. A higher percentage of patients with liver disease had abnormal PT ratios when their plasma was tested with the coagulometers than with the manual method. Transformation of PT ratios to International Normalized Ratios effectively eliminated the bias resulting from the different thromboplastin reagents but had no effect on the bias resulting from the different clot-detection methods. A significant proportion of patients appeared excessively anticoagulated (INR greater than 4.5) with the coagulometers but not with the manual method. These results highlight the need for standardization of both instrumentations and reagents to improve monitoring of oral anticoagulant treatment.

Effects of acute smoking on the hemostatic system in humans.

Habitual smoking is one of the best established risk factors for cardiovascular disease. The pathogenesis of smoke-induced damage is not so well clarified, but it probably includes--among some other aspects--an activation of the hemostatic system. Recently it has been shown that smoking a single cigarette can significantly decrease the coronary blood flow in coronary patients as well as in normal subjects. We tested the hypothesis that the acute effects of smoke are mediated by the hemostatic system. Seven healthy male volunteers, aged 20-40 years (mean 32 +/- 6 years), entered the study. All were habitual smokers, but had abstained from smoking in the 12 hours preceding the test. After lying in absolute rest for about 30 minutes, each subject smoked a cigarette containing 1.2 mg of nicotine. Immediately before and after smoking, blood was drawn by clear venipuncture for the evaluation of the following hemostatic variables: collagen-induced platelet aggregation by the method of Born; thromboxane B2 (TxB2) production by platelets stimulated with collagen, radioimmunoassay (RIA); plasma beta thromboglobulin (TG) (RIA); plasma fibrinopeptide A (FPA) (RIA); plasma fibrinolytic activity in the euglobulin fraction (NEF) (fibrin plate method). The following results, respectively before and after smoking, were observed: collagen-induced platelet aggregation 55 +/- 3 vs. 57 +/- 6%; TxB2 100.5 +/- 5.9 vs. 90.3 +/- 9.0 ng/10(8) platelets; plasma beta-TG 20.8 +/- 2.2 vs. 19.2 +/- 2.3 ng/ml; plasma FPA 2.3 +/- 0.3 vs. 2.2 +/- 0.1 ng/ml; NEF, lysis diameter 16.8 +/- 1.6 vs. 16.7 +/- 1.7 mm; NEF + C1 inhibitor lysis diameter 8.8 +/- 0.7 vs. 9.1 +/- 0.7 mm.(ABSTRACT TRUNCATED AT 250 WORDS)

Platelet function and thrombin activity in patients with recent cerebral transient ischemic attacks.

Platelet function and thrombin activity were investigated in 12 hospitalized patients (7 men and 5 women, mean age 53 years) who had had transient cerebral ischemic attacks in the previous 2-12 weeks. Each patient was given an extensive clinical and instrumental evaluation, including Doppler sonography of the cervical and lower limb vessels, cerebral angiography, and head computed tomography scan, after which relevant atherosclerotic disease was excluded. The controls consisted of 12 subjects hospitalized for nonvascular neurologic problems and matched for age, sex, and risk factors to the transient ischemic attack patients. Collagen-induced platelet thromboxane B2 production, plasma beta-thromboglobulin, and fibrinopeptide A were significantly higher in the patients than the controls. Platelet aggregability by collagen was the same in the 2 groups. Platelet hyperfunction and enhanced thrombin activity are present in patients some weeks after the acute episode, suggesting that the hemostatic system has a primary pathogenetic role.