title: Standardization of light transmittance aggregometry for monitoring antiplatelet therapy: an adjustment for platelet count is not necessary.
abstract: BACKGROUND
  Light transmittance aggregometry (LTA) is considered to be the 'gold standard' of platelet function testing. As LTA has been poorly standardized, we analyzed the results of LTA in healthy subjects and patients with antiplatelet therapy using different concentrations of agonists and performing tests in non-adjusted and platelet count-adjusted platelet-rich plasma (PRP).
  
  
  METHODS
  LTA was performed in 20 healthy subjects and in patients treated with aspirin (n = 30) or clopidogrel (n = 30) monotherapy, as well as in patients on combination therapy (n = 20), using arachidonic acid (ARA 0.25 and 0.5 mg mL(-1)) and adenosine diphosphate (ADP 2 and 5 microm) as agonists and performing platelet function tests in non-adjusted and platelet count (250 nL(-1) +/- 10%)-adjusted PRP.
  
  
  RESULTS
  The overall platelet aggregation response is decreased after adjusting the PRP for platelet count compared with measurements in unadjusted PRP. The variability of aggregation results is high in adjusted PRP in the subgroup of healthy subjects, ranging from 9.2-95.3% (5th-95th percentile) relative to 77.6-95.5% in non-adjusted PRP when determining maximum aggregation to ARA 0.5 mg mL(-1). Late aggregation using ADP 2 microm ranges from 3.8-89.9% in adjusted PRP compared with 42.9-92.5% in non-adjusted PRP. Maximum aggregation using ARA 0.5 mg mL(-1) in non-adjusted PRP differentiates between aspirin-treated patients and healthy controls well, whereas late aggregation using ADP 2 microm in non-adjusted PRP offers the best discrimination between clopidogrel-treated patients and healthy controls.
  
  
  CONCLUSIONS
  Adjustment of PRP for platelet count does not provide any advantage and therefore the time-consuming process of platelet count adjustment is not necessary.
authors.affiliation: J. W. Goethe University Hospital, Division of Vascular Medicine, Department of Internal Medicine, Frankfurt/Main, Germany. birgit.linnemann@kgu.de
authors.forename: B
authors.initials: B
authors.lastname: Linnemann
authors.forename: J
authors.initials: J
authors.lastname: Schwonberg
authors.forename: H
authors.initials: H
authors.lastname: Mani
authors.forename: S
authors.initials: S
authors.lastname: Prochnow
authors.forename: E
authors.initials: E
authors.lastname: Lindhoff-Last
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D016718:Arachidonic Acid / Q000494:pharmacology; D001241:Aspirin / Q000494:pharmacology / Q000627:therapeutic use; D002138:Calibration; D000077144:Clopidogrel; D005260:Female; D005343:Fibrinolytic Agents / Q000494:pharmacology* / Q000627:therapeutic use; D006801:Humans; D008297:Male; D008875:Middle Aged; D009391:Nephelometry and Turbidimetry / Q000379:methods*; D010974:Platelet Aggregation / Q000187:drug effects*; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology* / Q000627:therapeutic use; D010976:Platelet Count; D010979:Platelet Function Tests / Q000295:instrumentation / Q000379:methods / Q000592:standards*; D053657:Platelet-Rich Plasma; D012680:Sensitivity and Specificity; D019851:Thrombophilia / Q000097:blood / Q000188:drug therapy; D013988:Ticlopidine / Q000031:analogs & derivatives / Q000494:pharmacology / Q000627:therapeutic use
chemical_list: D005343:Fibrinolytic Agents; D010975:Platelet Aggregation Inhibitors; D016718:Arachidonic Acid; D000244:Adenosine Diphosphate; D000077144:Clopidogrel; D013988:Ticlopidine; D001241:Aspirin