In cases of suspicion of SM help can also be drawn from analysis of mutation in KIT(D816V) in peripheral blood using sensitive PCR-technologyTo set the diagnosis of systemic mastocytosis, certain criteria must be met. Either one major + one minor criterium or 3 minor criteria has to be fulfilled:

Major criterion
Dense infiltrates of >15 mast cells in the bone marrow or an extracutaneous organ

Minor criteria
Aberrant phenotype on the mast cells (pos. for CD2 and/or CD25)
Aberrant mast cell morphology (spindle-shaped)
Finding of mutation in KIT(D816V)
S-tryptase >20 ng/ml

Other mast cell diseases
Other types of mast cell disease include:

Monoclonal mast cell activation, defined by the World Health Organization definitions 2010, also has increased mast cells but insufficient to be systemic mastocytosis (in World Health Organization Definitions)
Mast cell activation syndrome – has normal number of mast cells, but all the symptoms and in some cases the genetic markers of systemic mastocytosis
Another known but rare mast cell proliferation disease is mast cell sarcoma. Classification
Mastocytosis can occur in a variety of forms:

Cutaneous mastocytosis (CM)
The most common cutaneous mastocytosis is maculopapular cutaneous mastocytosis, previously named papular urticaria pigmentosa (UP), more common in children, although also seen in adults. Telangiectasia macularis eruptiva perstans (TMEP) is a much rarer form of cutaneous mastocytosis that affects adults. [2] MPCM and TMEP can be a part of indolent systemic mastocytosis.
This should be considered if patients develop any systemic symptoms
Generalized eruption of cutaneous mastocytosis (adult type) is the most common pattern of mastocytosis presenting to the dermatologist, with the most common lesions being macules, papules, or nodules that are disseminated over most of the body but especially on the upper arms, legs, and trunk
Diffuse cutaneous mastocytosis has diffuse involvement in which the entire integument may be thickened and infiltrated with mast cells to produce a peculiar orange color, giving rise to the term "homme orange. "Cutaneous mastocytosis in children usually presents in the first year after birth and in most cases vanishes during adolescence. Systemic mastocytosis (SM)
Systemic mastocytosis involves the bone marrow in the majority of cases and in some cases other internal organs, usually in addition to involving the skin. Mast cells collect in various tissues and can affect organs where mast cells do not normally inhabit such as the liver, spleen and lymph nodes, and organs which have normal populations but where numbers are increased. In the bowel, it may manifest as mastocytic enterocolitis. However, normal ranges for mast cell counts in the gastrointestinal tract mucosa are not well established in the literature, and depend upon the exact location (e.g. right versus left colon), gender, and patient populations (such as asymptomatic patients versus patients with chronic diarrhea of unknown etiology). Quantitative mast cell stains may yield little diagnostic information, and further research studies are warranted to determine whether "mastocytic enterocolitis" truly represents a distinct entity.There are five types of systemic mastocytosis:
Indolent systemic mastocytosis (ISM).