I have some experience with it. What do you mean by “relatively stable”?

It’s my understanding that one reason MCAS is difficult to diagnose is because tryptase labs may appear normal unless you have them done while you’re having a flare. Unless the symptoms are very, very severe, it can be hard to capture this in the labs. So while it’s good to test, some providers use “empiric treatment” (basically trial and error) and if they suspect MCAS, and honestly you could even do this on your own because most of the medications are over the counter, they may have you try certain antihistamines regularly/preventatively to see if symptoms improve (and that’s what was implied by a Mayo Clinic provider) because it’s relatively low-risk to try.

I have POTS and HSD/hEDS, and MCAS is often part of it, so much so people call it “the trio.” The trouble is people can have milder symptoms of mast cell activation, so maybe the symptoms are still very limiting but not to the point of needing an epi pen, but that seems to be a very gray area and not much clarity or research. Feels like one of those situations where the labs tell only part of the story.

If you can and you suspect it, it’s probably best to see an allergist with experience with MCAS.

“A blood test to evaluate tryptase levels is often performed, particularly as it is a strong marker for mastocytosis and for HATs, but it is considered less specific for MCAS as many people affected by MCAS do not have high baseline tryptase levels. This means that their normal, everyday tryptase levels are not high. They may however be higher during a symptom flare or during anaphylaxis, but it can be challenging to obtain blood samples at this precise time for testing.”

You may have come across this, but this may help: https://www.mastcellaction.org/about-mcas#:~:text=Due%20to%20the%20allergic%2Dtype,blood%20sample%20for%20RAST%20testing.