Representative Normal and Abnormal LTA Tracings. Figure A shows normal responses to epinephrine 1.0 μM (curve 1) and collagen 2.0 mg/mL (curve 2). At critical concentrations, weak agonists such as epinephrine and ADP induce a biphasic response. The primary wave of aggregation reflects response to the addition of exogenous agonist. When normal platelets are activated, they secrete an endogenous pool of agonists. The secondary wave represents aggregation in response to this endogenous pool. Figure B is a tracing from a patient with epistaxis and menorrhagia. The response to ADP 5.0 μM (curve 1) is attenuated. A primary wave of aggregation is followed by deaggregation and an absent secondary wave of aggregation. There is no response to epinephrine 5.0 μM (curve 2). The patient’s platelets also demonstrated abnormal ATP secretion in response to ADP and epinephrine. Electron microscopy of the patient’s platelets revealed an absence of dense granules consistent with a diagnosis of dense granule storage pool disorder.