Validation of a procedure to assess ASA-response in patients with decreased, initial TRAP induced aggregation.

Whole blood aggregometry on the is a simple, fast and standardized method and it is widely used to assess platelet function under antiplatelet therapy. Reference ranges and a cut-off value as a measure of ASA response were established by measuring arachidonic acid induced aggregation (ASPI-test) in healthy volunteers and cardiac patients after and used to classify patients as ASA responders or non-responders. However, assessing the platelet function is highly affected by pre-analytical and analytical conditions and often reduced aggregation by TRAP induced aggregation (TRAP-test) is seen, rendering the samples difficult for interpretation of the ASPI-test and the responder status to ASA. We hypothesised that in this simplified model any preanalytical factor has the same effect on TRAP-testing as on ASPI-testing and that by calculating the ratio between a defined, normal TRAP-test result and the TRAP-test result measured for the individual patient this ratio could be applied to the measured ASPI-test thereby reaching a more valid discrimination between ASA responders and -non-responders. TRAP- and ASPI-test were performed in blood from ASA-treated volunteers and controls on Multiplate before an after pneumatic tube delivery as a model to stimulate shear stress induced platelet activation and aggregation. The calculated, normalised ASPI test result after tube delivery did not differ significantly from the initial ASPI test result although tube delivery had a significant impact on the measured ASPI test result. If applied to patients samples a definite judgement on the ASA response status of patients with reduced "general platelet activatability" could be given. Normalisation of the ASPI-test result using the TRAP-test result may provide a method to judge on the ASA response status in patients with decreased initial "general platelet activatability".