A KIT D816V mutation detection system is an in vitro diagnostic test intended for qualitative detection of KIT D816V mutational status from fresh bone marrow samples of patients with aggressive systemic mastocytosis using nucleic acid amplification and real time detection systems. The KIT D816V mutation detection system is indicated as an aid in the selection of aggressive systemic mastocytosis patients for whom Gleevec® (imatinib mesylate) treatment is being considered.