Clinical evaluation of new global clotting assay for monitoring of LMWH treatment: pilot study.

ABSTRACT

Until now, there has been no reliable method for the monitoring low molecular weight heparin (LMWH) therapy. Based on our observations of the coagulant activity of pseudoserum obtained after clotting of recalcified plasma from patients who were treated with LMWH, we were led to develop a new global clotting assay for the monitoring of this treatment. Methods description. After performing Howell time on PPP, samples were incubated for 30 min in 37 degrees C and they were then centrifuged for 10 min 0.2 ml of this pseudoserum is added to 0.2 ml of citrated normal plasma. Pseudoserum triggered coagulation of normal plasma and the time of new clot formation is expressed in seconds. This assay was called ATHU-test (AHEPA Thromb Haem Unit). We tested 21 normal subjects a in order to define the normal mean value and the range of the method. b) We also checked the reproducibility of the method by repeating the ATHU-test 17 times on the same normal plasma. c) We performed in vitro experiments to study its reliability and we added increasing concentrations using given doses of enoxaparine (4, 8, 12, 16 mg/ml) or fraxiparine (1.5, 3.0, 4.5, 6 u aXa/ml) which was added in vitro to normal plasma confirming the proportional linear regression between duration of our test and the amount of LMWH. Finally d) we checked on the therapy response and the LMWH levels in blood for thrombophiliacs. Results. a) NP, n=21, X=138.6+/-41.1, range 75-225 sec which means that values >X+/-3S=261.9 are distinctively pathological. b) The reproducibility of the method is acceptable, CV=9%. c) It is confirmed that in vitro addition of precautionary doses of LMWH (1.5 u aXa/ml) exceeds the coagulation time of ATHU-test up to 300 sec and it follows a distinctively proportional relationship. d) The monitoring of 20 thrombophiliacs for 2 months proved that i) All their test times were between 4-15 min. The more we approach the value of 15 min the more danger there is of haemorrhage while, on the contrary, the more values approach 4 min the more the danger of rethrombosis increases. We present the ATHU-test, a simple test which has been used for 6 months now by our Unit, in order to control the LMWH therapy for patients with thromboembolic diseases. The ATHU-test's reproducibility and its small range of normal values, the distinct relationship between therapeutic doses and therapeutic clinical results, as well as the in vitro proof of the linear regression between the coagulation time and the containing amount of LMWH, are likely to establish a new method of choice for the monitoring of LMWH therapy.