Even though new anticoagulants are being devised with the notion that they do not require regular monitoring, when bleeding occurs, it is important to have an antidote and a reliable test to confirm whether the anticoagulant effects are persisting. We examined the effects of five heparinoids, unfractionated heparin (UFH), tinzaparin, enoxaparin, danaparoid and fondaparinux on the traditional APTT and anti-Xa assays as well as on the calibrated automated thrombogram (CAT). We also studied the ability of protamine sulphate (PS), NovoSeven, FEIBA and FFP to reverse maximum anticoagulation induced by the different heparinoids. The CAT was the only test to detect the coagulopathy of all the anticoagulants. PS produced complete reversal of UFH, and this could be monitored with all three tests. Tinzaparin can also be completely neutralised in vitro with high doses of PS, but the maximum enoxaparin reversal achieved with PS is only approximately 60%. Fondaparinux does not significantly affect the APTT and PS has no significant effect on its reversal. Only NovoSeven was able to correct the fondaparinux induced CAT abnormalities whilst having no effect on the anti-Xa level. None of the reversal agents was very effective in danaparoid spiked plasma but NovoSeven, at high dose, increased the ETP by 40% and reduced the anti-Xa level from 0.93 to 0.78 IU/ml. We conclude that the CAT is superior to the traditional coagulation tests in that it not only detects the coagulopathy of all the heparinoids but can be also be used to monitor their reversal.

Summary Introduction Haemolysis, icterus and lipaemia (HIL) may affect haemostasis test results. This may be influenced by the level of interfering substance and the reagents and end‐point detection system used. Methods We assessed the influence of HIL on prothrombin time, activated partial thromboplastin time and fibrinogen assay using a viscosity‐based detection analyser. Results Spontaneous haemolysis that occurred during sample collection and processing had no effect on PT with either a rabbit tissue factor extract or recombinant human tissue factor reagents. In contrast, addition of mechanically haemolysed cells impacted on PT for the highest haemoglobin concentration. For APTTs determined with STA®‐Cephascreen® reagent, there was no significant difference between results in haemolysed and nonhaemolysed samples. For the other two reagents studied, APTTs were statistically significantly shorter in haemolysed samples compared with nonhaemolysed samples. This bias was clinically significant only for STA®‐PTT Automate. For all three APTT reagents, the impact of haemolysis was sufficient to impact patient management decisions, and in some samples, the effects of lipaemia and icterus were not clinically significant. Conclusion Overall, our results confirm that PT and fibrinogen were not clinically significantly affected by HIL. The APTTs of some haemolysed samples were falsely normal. Haemolysed samples for APTT determination should be rejected.

Summary Atrial fibrillation (AF) is a common cardiac arrhythmia with a 5–20% annual risk of stroke. Warfarin reduces this risk by at least 60%. Despite adequate anticoagulation within the target International Normalized Ratio (INR) range of 2·0–3·0, some patients still experience thrombotic and bleeding events. It is now possible to assess the intensity of anticoagulation with automated thrombin generation (TG) tests, such as the calibrated automated thrombogram (CAT). These tests were compared and an inverse relationship was found between the INR and CAT in 143 elderly AF patients. There was equally good correlation between the concentration of factors II, VII, IX and X and the INR and TG parameters. The peak thrombin was most strongly associated with the concentration of prothrombin fragment 1 + 2 in plasma. There was wide variability in TG parameters in patients with identical INR values, sometimes up to a fourfold difference. This TG variability in individuals with the same INR is not due to inflammation, at least when the latter is measured as the concentration of factor VIII coagulant activity, von Willebrand factor antigen, high sensitivity C‐reactive protein and fibrinogen. It was concluded that, although the TG and INR were closely correlated there was wide variability in peak thrombin and endogenous thrombin potential in patients within the INR therapeutic range, the cause of which remains unclear.

This review has demonstrated that no significant coagulation factor deficiency would be left undiagnosed if the protocol was followed. This would have considerably reduced the cost and time spent performing these assays.

Background International normalized ratio (INR) is traceable to World Health Organization (WHO) International Standards for thromboplastins. International Standards must be used with a manual tilt tube technique (MTT) for prothrombin time (PT) determination. An important part of the total variability of INR is due to poor harmonization of MTT across WHO reference laboratories. Objectives To determine the origins of PT differences between operators performing MTT and to develop a harmonized MTT. Methods Two workshops were held where WHO reference laboratory operators could compare their PTs using MTT and the same equipment. A harmonized MTT was used by seven operators in the second workshop. Results Differences have been observed in tilting frequency and in the height of pipetting plasma in the test tube. At the beginning of the first workshop, the tilting cycle time varied between 1.1 and 2.7 seconds. The mean PT of normal plasma obtained by pipetting plasma at the top of the tube was 14.3 seconds but was 12.9 seconds when plasma was pipetted at the bottom of the tube. When using the harmonized MTT for WHO International Standard rTF/16, the differences between operators were not greater than 1.1 seconds in normal plasma, and not greater than 1.3 seconds in patient plasma with average INR of 3.0. INR between‐operator coefficient of variation was 2.3%. Conclusion Application of a harmonized MTT in three reference laboratories resulted in substantial reduction of between‐operator variation of PT and INR. The harmonized MTT is proposed as Candidate Reference Measurement Procedure.