Standardization of light transmittance aggregometry for monitoring antiplatelet therapy: an adjustment for platelet count is not necessary

• Published in: Journal of thrombosis and haemostasis Vol. 6; no. 4; pp. 677 - 683
• Main Authors: LINNEMANN, B., SCHWONBERG, J., MANI, H., PROCHNOW, S., LINDHOFF‐LAST, E.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.04.2008
• Subjects: Adenosine Diphosphate - pharmacology; Adult; Aged; Aged, 80 and over; Algorithms; Arachidonic Acid - pharmacology; aspirin; Aspirin - pharmacology; Aspirin - therapeutic use; Calibration; clopidogrel; Female; Fibrinolytic Agents - pharmacology; Fibrinolytic Agents - therapeutic use; Humans; light transmittance aggregometry; Male; Middle Aged; Nephelometry and Turbidimetry - methods; Platelet Aggregation - drug effects; Platelet Aggregation Inhibitors - pharmacology; Platelet Aggregation Inhibitors - therapeutic use; Platelet Count; Platelet Function Tests - instrumentation; Platelet Function Tests - methods; Platelet Function Tests - standards; Platelet-Rich Plasma; responsiveness; Sensitivity and Specificity; standardization; Thrombophilia - blood; Thrombophilia - drug therapy; Ticlopidine - analogs & derivatives; Ticlopidine - pharmacology; Ticlopidine - therapeutic use
• ISSN: 1538-7933; 1538-7836; 1538-7836
• DOI: 10.1111/j.1538-7836.2008.02891.x

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 μm) 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 μm 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 μm in non‐adjusted PRP offers the best discrimination between clopidogrel‐treated patients and healthy controls. Conclusion: Adjustment of PRP for platelet count does not provide any advantage and therefore the time‐consuming process of platelet count adjustment is not necessary.