Mastocytosis is exceedingly rare - an article in NEJM (one of the authoritative medical journals) estimates that 1 in 100,000 people have been diagnosed with th

Mastocytosis is exceedingly rare - an article in NEJM (one of the authoritative medical journals) estimates that 1 in 100,000 people have been diagnosed with the disease. If your primary care physician has 2,000 patients (not unreasonable), s/he could reasonably expect to never encounter the disorder outside of a textbook. Just as in programming, doctors avoid the 'premature optimization' - no need to test for a rare disorder until considerably more common ones, like allergies, are ruled out.