Mast cell activation syndrome will be confirmed if the following three conditions are met (according to Valent et al, 2012) :

• At least two clinical signs compatible with MAS before the first consultation (V1)
• Improvement of symptoms on antihistamines within 2 months of initiation of treatment
• Significant increase in tryptase during crisis

Mast cell activation syndrome will be possible if :

• At least two clinical signs consistent with MAS before the first consultation (V1)
• Improvement of symptoms with antihistamines within 2 months of initiation of treatment
• No significant increase in tryptase during crisis In all other cases, mast cell activation syndrome is unlikely.

The presence of mast cell activation syndrome will be described in three modalities : confirmed, possible, and unlikely.

Mast cell activation syndrome will be confirmed if the following three conditions are met :

• at least two clinical signs compatible with mast cell activation syndrome (MCAS) before the first consultation (V1)
• improvement of symptoms with antihistamines within 2 months of initiation of treatment
• significant increase in tryptase during crisis

Mast cell activation syndrome will be possible if:

• at least two clinical signs compatible with MCAS before the first consultation (V1)
• improvement of symptoms under antihistamine at 2 months of the introduction of the treatment
• no significant increase in tryptase during crisis In all other cases, mast cell activation syndrome is unlikely.

Symptoms are those established by Valent et al, 2012. For each clinical sign the patient will rate the frequency of the symptom: more than once a day, once a day, 2 to 6 times a week, once or less a week, never, over the two months prior to visit 1 (V1), and between V1 and the 2-month follow-up visit .