Genetic studies of platelet reactivity (PR) phenotypes may identify novel antiplatelet drug targets. However, discoveries have been limited by small sample sizes (n<5,000) due to the complexity of measuring PR. We trained a model to predict PR from complete blood count (CBC) scattergrams. A GWAS of this phenotype in 29,806 blood donors identified 21 distinct associations implicating 20 genes, of which six have been identified previously. The effect size estimates were significantly …