MCAS testing
MCAS testing can be challenging because mast cell mediators may only be elevated during an MCAS episode and then return to normal levels. Therefore, the test needs to be done when the symptoms of MCAS are present.
The specific mediators of interest, and the thresholds required to attribute MCAS, are the subject of ongoing research and debate among the medical community.
No single mediator test is definitive; a positive result is not to say that a person certainly has MCAS and, similarly, a negative result is not sufficient to rule out an MCAS diagnosis. However, when considered alongside other diagnostic evidence, these mediator tests can provide reasonable confidence in a diagnosis.
Blood tests for MCAS: In most individuals with MCAS, serum tryptase levels remain within the normal range but are elevated in HaTS & mastocytosis.
Urinary tests for MCAS
N-methyl histamine is a good specific marker for mast cells but is also present in basophils.
Prostaglandins are not specific to mast cells so not recommended as a single marker. A positive test in one prostaglandin suggests nonclonal MCAS, whereas a positive result for all three (DM, D2, F2a) suggests clonal MCAS.
Catecholamines can also be tested with a 24-urine test, which can help to rule out other pathologies.
Elevated results are suggestive of a MCAS diagnosis. Normal results do not rule out MCAS. For further information about testing, please refer to our testing leaflet and please feel free to share our testing leaflet for patients.
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