Diagnostic criteria for mast cell activation syndrome include all of the following: Typical clinical symptoms of mast cell mediator release During symptoms, a substantial transient increase in total serum tryptase level or an increase in other mast cell-derived mediators, such as N - methyl histamine or prostaglandin D2, leukotriene E4, or their urinary metabolites A clinical response to drugs that attenuate the production or activities of mast cell mediators Patients with mast cell activation typically have a normal bone marrow biopsy if it is done.