Abstract: Provided herein are methods for detecting the presence of human pFLT3 in a sample. An exemplary assay provided herein is an ELISA method (e.g., sandwich ELISA). Also provided herein are methods for detecting FLT3 phosphorylation in a sample, diagnosing a patient having a FLT3-activating mutation, identifying a compound that activates or is otherwise and agonist of human FLT3 phosphorylation, identifying a compound that inhibits or is otherwise an antagonist of human FLT3 phosphorylation, determining the efficacy of a compound for increasing, decreasing or otherwise modulating human FLT3 phosphorylation in a patient. Further provided are kits for carrying out the said methods. Such kits comprise at least a total FLT3 antibody optionally immobilized on a solid support and a labeled pFLT3 antibody.