What is the difference between mast cell activation syndrome and mastocytosis?

Mast cells: Mast cell activation may be a prerequisite for mastocytosis, the latter has specific criteria for diagnosis. http://emedicine.medscape.com/article/1057932-workup.

Yes they Differ.: These are two separate conditions. Symptoms may be similar but the cause is different. In mastocytosis, patients have too many mast cells(MC). Because they are so plentiful, when one activates the other MC close by, will also release their chemicals (Histamine, Leukotrienes, prostaglandins, etc). MCAS is a condition that the numbers of MC are normal but overactive. Degranulating spontaneously.