Reagent-supported thromboelastometry (TEM) with the ROTEM Whole Blood Haemostasis Analyser is an enhancement of thromboelastography, a method that is increasingly used for the point of care monitoring of acute perioperative bleeding disorders. We investigated the reference ranges of two activated tests (INTEM and EXTEM) and a test analysing specifically the fibrin component of coagulation (FIBTEM) in a multi-centre approach. The reference ranges obtained for the clotting time (CT), clot formation time (CFT), alpha angle (ALP), maximum clot firmness (MCF) and clot lysis parameters were comparable from centre to centre. INTEM: CT equals; 137-246 s, CFT equals; 40-100 s, MCF equals; 52-72 mm. EXTEM: CT equals; 42-74 s, CFT equals; 46-148 s, MCF equals; 49-71 mm. FIBTEM: MCF equals; 9-25 mm. ROTEM whole blood coagulation correlated weakly with a trend towards enhanced coagulation in females compared with males and in advanced age. The repeatability (within-run imprecision) of the results was dependent on the test with the following coefficients of variation: 1-5% (clot firmness, alpha angle), 3-12% (CT, CFT), 6-13% (FIBTEM clot firmness). Citrated blood samples were stable for ROTEM analysis stored within 6 h from drawing. In summary, the data showed that ROTEM thromboelastometry yields consistent values between centres and that providing general orientating reference ranges seems to be possible.
SummaryA new PT reagent based on recombinant human tissue factor and synthetic phospholipids (phosphatidyl choline and phosphatidyl serine) with defined fatty acid side chains was calibrated against BCT/253 and CRM 149R. A small but consistent bias in the International Sensitivity Index (ISI) value was obtained using either the human or rabbit brain reference material. ISI values were around 1.0 or slightly lower depending on the respective instrument. Mixing studies with factor deficient plasmas showed a high factor sensitivity especially for factor VII as compared to commercial rabbit brain or human placenta thromboplastin. In an international field trial the reagent was tested using fully or semi automated Electra™ coagulometers in 4 different laboratories. Results with normal samples were in excellent agreement among the different laboratories. Mean values were 10.9, 10.9, 11.0, 11,7 s with a range of 9.5 to 12.5 s. Results of males and females were not different. In patients with liver disease very similar PT activities were found as compared to sensitive rabbit brain or human placental thromboplastins. In normals and patients with oral anticoagulation INR values correlated very well against BCT (r = 0.98, regression line y =-0.07 + 0.9 x). The distribution of samples was linear over the whole range. In the comparison against sensitive rabbit brain thromboplastin or human placental thromboplastin similar correlations were found. In a few cases higher INR values were observed for the recombinant reagent especially in patients with intensive treatment. Factor assays in those patients showed at least the strong reduction of one vitamin Independent coagulation factor. Over all the linearity was better against the rabbit brain reagent than against the human placental reagent which is slightly less factor VII sensitive as shown in mixing studies with normal and factor VII deficient plasma. Precision studies in the 4 laboratories showed excellent reproducibility of lyophilised controls or local patient plasma pools for all reagents with a better performance of the recombinant reagent. C. V. values from day to day ranged from 1.3% to 5% for normal and abnormal controls.These results show that the recombinant PT reagent, especially in conjunction with a precise automated instrument, may improve the results of PT testing and thus may lead to better patient care.
Monitoring of direct thrombin inhibitors (DTIs) in patients with heparin-induced thrombocytopenia (HIT) is primarily performed using the activated partial thromboplastin time (aPTT). This assay is poorly standardized, reagent dependent, and not DTI specific. We compared aPTT, thrombin time (TT), and prothrombin time (PT) to drug levels obtained by the ecarin chromogenic assay (ECA). We analyzed 495 samples of patients with confirmed or suspected HIT on treatment with either argatroban (n = 37) or lepirudin (n = 80). Mean DTI levels ± standard deviation (SD) were 0.41 ± 0.36 µg/mL for argatroban and 0.20 ± 0.21 µg/mL for lepirudin. Results of aPTT were highly variable: 67 ± 22 seconds for argatroban and 55 ± 20 seconds for lepirudin. Significant correlations ( P < .01) were found between ECA-based DTI level and TT (argatroban, r = .820 and lepirudin, r = .830), PT (argatroban, r = -.544), and aPTT (lepirudin, r = .572). However, there was no correlation of aPTT with argatroban or PT with lepirudin concentration. Multiple regression analyses revealed that the TT predicted 54% of argatroban and 42% of lepirudin levels, but no significant impact was seen for PT or aPTT. The aPTT-guided monitoring of DTI therapy leads to a high percentage of patients with inaccurate plasma levels, hence resulting to either undertreatment or overtreatment. Knowledge of baseline values prior to DTI therapy and inclusion of clinical settings are essential for dosing DTIs when using aPTT. However, due to several limitations of aPTT, monitoring according to exact plasma concentrations as obtained by specific tests such as ECA may be more appropriate.
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