phenotype affects entity platelet aggregation Impaired platelet aggregation Defective platelet aggregation HP:0008177 HP:0003540 An impairment in the rate and degree to which platelets aggregate after the addition of an agonist that stimulates platelet clumping. Platelet aggregation is measured using aggregometer to measure the optical density of platelet-rich plasma, whereby platelet aggregation causes the plasma to become more transparent. Deficient platelet aggregation Platelet aggregation defect UMLS:C1855853 Abnormal platelet aggregation decreased platelet aggregation platelet aggregation phenotype