I am happy to answer your question, Gail. Those of us with MCAS or Idiopathic Anaphylaxis, for example, usually have completely normal histamine/tryptase levels. Yet, we can be extremely ill, shocking, and even be debillitated and unable to barely walk. That describes me before I was diagnosed and put on meds.
Those who have Masto either have mutated mast cells or way too many mast cells. Those with MCAS or IA react like the Masto people, but our mast cells are normal in shape and number. They just seem to be way too sensitive for some unknown reason and thus we shock and are just as ill as Masto people. The docs test us and all of our levels are normal. Yet we are oh so sick with Masto symptoms. So, the docs (I am referring to the main Masto researchers) put us on the same meds that they put the Masto people on. Everyone reacts to a different combination of meds best, because what would the fun in it be if it was easy?
So, they generally start all of us with some combination of Zantac, Zyrtec, and/or Allegra, and they then start tinkering by adding others such as Singulair, Gastrocrom, Hydroxyzine, etc. The doctors use their own knowledge to design a combo that works best for their individual patient since we all respond differently to the various meds.
Some people respond better to Zantac, while others do better with Pepcid. Some use both Allegra and Zyrtec and others use just one of those. Some use high doses of Hydroxyzine and others use tiny doses. It all depends upon finding the right combo with the help of the doctor. All of these are based on the symptoms and the responses, however, not the tryptase levels since we IA or MCAS patients have great normallevels....we are just really sick without those meds, though.
I hope this helps explain it a bit.