Platelet high reactivity in the LTA induced by a low-response concentration (0.5 μM) of ADP and epi and association with other platelet function parameters. (A) Discrimination of high and low responders to platelet aggregation induced by ADP and epi. The cutoffs for defining platelets from participants as low-responsive and high-responsive to low-response concentrations of ADP (0.5 μM) and epi (0.5 μM) measured by LTA were established as an intersection of 2 Gaussian distributions. Left: blue curve: mean = 21.72, SD = 10.06, weighting in the Gaussian mixture distribution = 0.84. Red curve: mean = 81.65, SD = 12.38, weighting in the Gaussian mixture distribution = 0.16, cutoff = 52.31%. Right: blue curve: mean = 35.22, SD = 17.24, weighting in the Gaussian mixture distribution = 0.38. Red curve: mean = 88.35, SD = 5.53, weighting in the Gaussian mixture distribution = 0.62, cutoff = 73.2%. (B) Distribution of study participants for maximal platelet aggregation responses to low-response concentrations of ADP (0.5 μM) and epi (0.5 μM). Four groups of study participants with distinct platelet reactivity patterns to low concentrations of ADP and epi were identified (Q1-Q4): Q1, high responsive to ADP and low responsive to epi; Q2, low responsive to both ADP and epi; Q3, low responsive to ADP and high responsive to epi; Q4, high responsive to both ADP and epi. (C-D) Associations between platelet aggregation in response to low-response concentrations of ADP (0.5 μM) and/or epi (0.5 μM) and parameters of other platelet function tests regulated by Gi protein–coupled receptor signaling. (C) ADP$±$ epi, (D) epi were investigated using Poisson regressions with robust standard errors. The model was adjusted for age, sex, platelet count (whole blood), and platelet function-interfering medications. CAT, calibrated automated thrombinography; CI, confidence interval; FACS, flow cytometry; MFI, mean fluorescence intensity; PFA, platelet function analyzer; TRAP-6, thrombin receptor–activated peptide 6.