The MastAttack 107: The Layperson’s Guide to Understanding Mast Cell Diseases, Part 35

Author’s note: This is not medical advice. Any information found here should be used as a tool for discussions you have with a provider who knows you and your specific health situation.

42. How is anaphylaxis related to mast cell disease? How do I know when to use my epipen?

Anaphylaxis is a complication of mast cell disease. It is not an inherent part of mast cell disease or a symptom of mast cell disease. Many patients never experience it.

One study found that among mastocytosis patients, adult patients with SM are more likely to experience anaphylaxis than adults with CM or children with mastocytosis. But as many as half of adult patients and even more pediatric patients never have anaphylaxis. For MCAS, the number is reported as less frequent with incidence of anaphylaxis in one group around 17%. I personally think this number is very low and sampling error. It is my experience that MCAS patients are at least as likely to anaphylax as mastocytosis patients, if not more likely.

Even though lots of mast cell patients never experience it, it is important to be aware of the risk of anaphylaxis and take precautions. Mast cells are critical in the biology of anaphylaxis so having mast cells that are very reactive, or having more mast cells than usual, can lead to more severe anaphylaxis more often than someone in the general population might experience. All mast cell patients should carry two epipens at all time. They should also carry diphenhydramine (Benadryl, liquid preferred), and many also carry steroids to use in case of anaphylaxis.

One of the most common questions I am asked is when to use your epipen. The answer to this is complicated largely because so many symptoms of mast cell disease are also symptoms of anaphylaxis. It can be hard to figure out what is going on. I have written extensively about the difference between anaphylaxis and mast cell reactions before so I recommend you read those posts also if you have not already.

The answer to when you should use your epipen is pretty much always that you should ask your doctor or provider. This answer is true and is always right. It is important that someone who knows your health situation well weighs in.

But there’s another answer we can give to this question: that you should use you epipen when it will save your life.

There are various charts and scales that people and groups use to categorize the severity of anaphylaxis. These are not useful for mast cell disease. Do not use them. They are meaningless for us.

The purpose of those charts is to allow people to figure out when a bad anaphylaxis episode is on the way. It allows people to estimate by symptoms when they should use their epipen and call 911. The charts are saying, if you have these three symptoms, you could be heading for anaphylaxis, use your epipen. But for mast cell patients, you can have those three symptoms for a variety of reasons that are not anaphylaxis. It could be mast cell reaction or just regular symptoms. So mast cell patients can’t really predict anaphylaxis in the way described in the charts. These charts just do not work for us.

So when should mast cell patients use an epipen? Generally, the answer is that they should use it when they have trouble breathing or a significant drop in blood pressure. If you are looking for independent markers for when to use an epipen and not symptoms, this lines up with a pulse ox of below 91, or systolic blood pressure below 90 (for adults), or a 30% drop in blood pressure from baseline (for children or adults). Speaking abstractly, in mast cell patients, trouble breathing and significant drop in blood pressure are usually considered as signs of anaphylaxis that warrant use of an epipen. Additionally, if the patient has a set of symptoms that they know will lead to trouble breathing or low blood pressure, their provider will direct them to use an epipen as soon as those symptoms start.

Again, when you use an epipen is a discussion that you must have with your provider. Mast cell patients should all carry two epipens on them at all time and whatever else they use for rescue meds, usually liquid diphenhydramine, and sometimes other medications.

For more detailed reading, please visit these posts:

The definition of anaphylaxis

Anaphylaxis and mast cell reactions

Treatment of anaphylaxis