Mast Cell Activation Syndrome (MCAS)

About Mast Cell Activation Syndrome (MCAS)

In Mast Cell Activation Syndrome (MCAS) patients have a normal or nearly normal number of mast cells but their cells react too readily, and out of proportion with the perceived threat to the body.  The signs and symptoms of mast cell activation syndrome are thought to be caused by the episodic release of inflammatory mediators from mast cells. Some patients present with recurrent episodes of anaphylaxis for which a consistent trigger or cause may or may not be identified. At the present time we are unable to estimate the number of people with Mast Cell Activation Syndrome because there is not enough data.

Diagnosis of MCAS

Diagnosis of MCAS can be a challenge because the mast cell mediators (chemicals released by the cells) may only be elevated during an episode and then return to normal levels.  While some people with symptoms of MCAS have a raised serum tryptase level, a number of people with a similar set of symptoms   may have it elevated only during a flare of symptoms with it returning to baseline, or it may not be elevated at all.

Some doctors in the UK are now able to test other mast cell mediators such a histamine and prostaglandins in the urine.  These tests for mast cell mediators include spot or 24-hour urine testing for n-methyl histamine, prostaglandin D2 or beta prostaglandin F2-alpha. These tests are done by specialist laboratories and samples must be handled properly.

Response to anti-mediator treatments (H1 and H2 antihistamines, anti-leukotriene or anti-prostaglandins) is an additional indicator of mast cell involvement, though some MCAS patients also react to inactive ingredients in medications, making it difficult to discern a positive response.

Symptoms of postural orthostatic tachycardia syndrome (POTS) and Ehlers-Danlos Syndrome (EDS) are being increasingly being identified in a group of MCAS patients.