Is platelet aggregation testing dependent on fibrinogen level?
L. Graf, J. Worden, W. Korte (1St. Gallen, Switzerland)
Time: 17:15 - 18:15
Objective: Bleeding disorder work up usually includes screening for clotting factor deficiencies, von Willebrand disease (vWD), and platelet disorders. Testing for platelet disorders is often done by light transmission aggregometry (LTA). In order to reduce variability, a lot of laboratories perform LTA on platelet rich plasma with adjusted platelet count. We studied the influence of other parameters of coagulation to LTA-results.
Methods: Patients being referred to our center for bleeding disorder work up were included pospectively in this study. Every patient underwent basic coagulation work up (prothrombin time (PT), activated partial thromboplastin time (aPTT), fibrinogen, and factor XIII), testing for vWD (von Willebrand factor activity, von Willebrand factor antigen, and factor VIII) as well as testing for platelet disorders by LTA using platelet rich plasma samples adjusted to a standardized platelet count between 200 and 300G/l. To induce aggregation ADP, collagen, epinephrin, and ristocetin were used in different concentrations. Dependence of % maximal aggregation (MA) results from other coagulation parameters were investigated using mutiple regression analysis.
Results: 48 patients were evaluated prospectively. MAs induced by ADP in high (10μM) and medium (5 μM) concentration were significantly dependent on fibrinogen level (p=0.02 for ADP10μM and p=0.01 for ADP5 μM) but not on all other coagulation parameters. Fibrinogen levels were in the normal range for all patients tested (1.5-3.5g/l). MAs induced by all other agonists used were not related to any other coagulation parameter.
Conclusion: Our results suggest that platelet aggregation induced by ADP is dependent on fibrinogen concentration in plasma (even if fibrinogen concentration is within the normal range). Given these results, one could speculate that adjustment for a defined fibrinogen level might improve variance of LTA. Furthermore, fibrinogen concentrations might influence efficacy of platelet inhibition with ADP-receptor antagonists.