Thromboelastographic Evaluation of Recombinant Factor VIIa in a Child with Glanzmann??s Thrombasthenia

To the Editor: Glanzmann's thrombasthenia (GT) is a rare autosomal recessive inherited disorder of platelet function (1). Recombinant factor VIIa (rFVIIa; NovoSeven) has been introduced as an alternative to platelet transfusion in patients with GT-associated bleeding (2–5). Conventional laboratory tests of hemostasis, prothrombin time, and activated partial thromboplastin time show normal values in GT patients; they are not influenced by rFVIIa administration. We used thromboelastography (TEG®; Haemoscope, Niles, IL) to monitor the effects of rFVIIa on hemostasis in an 11-yr-old boy with GT referred to our hospital for orchidopexy. To reduce perioperative bleeding, we administered an IV bolus of 90 μg/kg rFVIIa 10 min before surgery. We recorded TEG® tracings before and after administering rFVIIa (Figure 1). We repeated the dose twice at 2-h intervals after surgery. The patient recovered without excessive bleeding. No adverse events were observed during 6-mo follow-up. Repeated TEG® (Figure 1) at 6 mo showed values comparable to those at baseline, except for a longer reaction time (r): 73.3 versus 49.3 min.Figure 1.: Thromboelastographic tracing (normal values) of a patient with Glanzmann's Thrombasthenia 10 min before (A) and 10 min after (B) a bolus injection of 90 μg/kg rFVIIa. Reaction time value (r, 12–27 min) at baseline normalized from 49.3 min to 23.2 min, coagulation time value (k, 3–13 min) at baseline normalized from 33 min to 10.8 min and α angle (α, 14°– 6°) at baseline normalized from 6.5° to 20.2°. The maximal amplitude (MA, 42–63 mm) increased from 33.8 mm at baseline to 36.4 mm. Repeated thromboelastographic tracing (C) at 6 mo showed values comparable to those at baseline, except for the prolonged reaction time (r) value: 73.3 min versus 49.3 min.In contrast to conventional laboratory test results, TEG® clearly showed a defect in this GT patient's hemostasis. Prolonged r and k values and a decreased α-angle indicated delayed clot formation, and a decreased maximum amplitude (MA) value indicated impaired clot strength. After we administered rFVIIa r, k, and α, values normalized, and the MA improved, though the latter did not normalize. These findings suggest normalized speed of clot formation and improved clot strength. In GT patients, dosages and number of doses of rFVIIa administration are based on the clinical response, i.e., stopping or preventing bleeding. Clinical titration can result in over- or under-dosage of rFVIIa and conflicting treatment protocols (2–5). Moreover, GT patients can be classified according to the number of platelet glycoprotein IIb/IIIa receptors expressed on their platelet surface. Bleeding tendency in GT patients may vary accordingly. TEG®, which may enable both identification and quantification of the hemostatic defect in GT patients, can be used as a simple test to monitor the effects of corrective treatment. F. Ismael Department of Anaesthesiology J. van der Meer Division of Hemostasis, Thrombosis and Rheology J. Th. M. de Wolf Department of Hematology K. Kuizenga L. P. H. J. Aarts H. G. D. Hendriks Department of Anaesthesiology University Medical Centre Groningen Groningen, the Netherlands [email protected]