The clotting of a snake (Crotalus viridis Helleri) plasma and its interaction with various snake venoms.

The clotting of C. V. Helleri plasma is not accelerated by the factor X activator or thrombin-like enzymes from its own venom. Clotting of the plasma is accelerated by the factor Xactivator from Russell's viper venom, but not by the thrombin-like enzyme from Agkistrodon Rhodostoma venom ("Arvin"). The prothrombin activator from the Taipan venom clots C.V. Helleri plasma equally well as human plasma, but the thrombin which is produced has a marked specificity for its own fibrinogen, and clots bovine fibrinogen more slowly. C.V. Helleri plasma contains an inhibitor which progressively inactivates bovine factor Xa and thrombin, but the inhibitor is not potentiated by heparin. The slow, protracted clotting of the snake plasma either alone or when mixed with human plasma or bovine fibrinogen suggests that this inhibitor may interfere with the polymerisation of fibrin monomer.

Multicenter evaluation of lyophilized and deep-frozen plasmas for assignment of the International Normalized Ratio.

The interlaboratory variation of the International Normalized Ratio (INR) in various external quality assessment schemes is still relatively high. This is partly caused by inaccuracy of manufacturers' stated International Sensitivity Index (ISI) and/or local instrumentation effects. The interlaboratory variation and accuracy of INR determinations may be improved by a local calibration procedure based on lyophilized plasmas with assigned INRs. The purpose of the present study was to determine INR values for different types of lyophilized plasmas to be used for local calibration. A total of 13 lyophilized plasmas (one normal, six from coumarin-treated patients, six artificially depleted) were analyzed by 10 laboratories, each using five calibrated prothrombin time (PT) systems. INRs were calculated for each plasma using each laboratory's specific ISI and mean normal prothrombin time values. In the same way, five deep-frozen pooled plasmas from coumarin-treated patients were analyzed. There were significant INR differences for the lyophilized plasmas between the prothrombin time systems. The differences were relatively small for the deep-frozen coumarin plasmas (CV 2.6-3.3%) and three lyophilized coumarin plasmas from one manufacturer (CV 3.7-4.8%). Important INR differences were observed for three lyophilized coumarin plasmas from another manufacturer (CV 9.5-14.1%) and several artificially depleted plasmas (CV 5.3-12.8%). The citrate concentrations in the artificially depleted plasmas were lower than those in the normal and coumarin plasmas. These differences should be considered in the selection and certification of plasmas as calibrants for local calibration of PT systems. The lyophilized plasmas' INR values obtained in the present study will be used for a field study of local PT calibration to assess their efficacy.

Influence of three types of automated coagulometers on the international sensitivity index (ISI) of rabbit, human, and recombinant human tissue factor preparations--a multicenter study.

Five tissue factor reagents and three types of automated instruments for prothrombin time (PT) determination were studied in an international multicenter collaborative exercise. The purpose of this work was to determine the international sensitivity index (ISI) for each combination of reagent and instrument against the international reference preparation RBT/90. Each type of instrument was used by 3 or 4 centers to assess the interlaboratory variation of the ISI. The interlaboratory variation of the ISI for each combination of reagent and instrument ranged between 0.4% and 7.8% coefficient of variation. For three reagents, the mean ISI values for ACL (nephelometric) and STA (mechanical) were practically identical, but the mean ISI values for MLA (photo-optical) were at least 10% higher. For two other reagents prepared from rabbit tissue, the mean ISI values increased in the order ACL, STA, MLA. The widest range of mean ISI values was noted with one rabbit tissue factor reagent: 1.68 for ACL and 2.00 for MLA. Exclusion of patient specimens with INR <1.5 and INR >4.5 determined by the international reference preparation resulted in a slight decrease of the mean ISI. The interlaboratory variation of the International Normalized Ratio (INR) was assessed from the results obtained with common lyophilized and deep-frozen plasmas. The use of instrument-specific ISI values resulted in reduced interlaboratory variation of the INR. It is recommended that thromboplastin manufacturers provide instrument-specific ISI values.

An investigation of three patients with Christmas disease due to an abnormal type of factor IX.

Three patients with Christmas disease whose plasma was shown to have a prolonged one-stage prothrombin time with ox brain thromboplastin have been investigated. These patients have an inhibitor for the reaction between factor X, factor VII, and ox brain extract. The abnormal constituent responsible for this inhibitor appears to be factor IX whuch is functionally inactive but antigenically indistinguishable from normal factor IX. It is proposed that patients might be classified into haemophilia B(+) for patients with this defect (Christmas disease(+)) and haemophilia B(-) (Christmas disease(-)) for patients who have classical Christmas disease.

An attempt to standardize the APTT for heparin monitoring, using the P.T. ISI/INR system of calibration. Results of a 13 centre study.

Five APTT reagents, a heparin clotting assay and a chromogenic assay have been tested at 13 centres using lyophilised plasma containing different levels of added heparin (in vitro samples), and fresh normal plasma samples and samples from patients receiving heparin therapy (ex vivo samples). Marked differences in sensitivity between the reagents to in vitro and ex vivo samples were found. When calibration of the reagents was attempted using orthogonal regression analysis based on the P.T. ISI/INR system, the results were disappointing. Whichever reagent was accepted as standard, the between laboratory differences in ISI's were very large, and the within laboratory and between laboratory CV's were unacceptably high. Regression lines through normal and patient clotting times were commonly non parallel or skewed. From the results of only 5 out of more than 30 commercial reagents, it is concluded that the application of such a system would give no confidence in any individual result and could be misleading.