How do you counsel a patient on returning to the care of their PCP when a workup for MCAS has been unrevealing, but the patient insists that they have a mast cell disorder because they respond to antihistamine therapy?

At the end of the day, the treatment approach is the same as with mast cell activation syndrome (MCAS). There are additional relevant codes that can be helpful for these patients including 'mast cell activation, unspecified', and 'other mast cell activation disorders'.