TMPRSS11D and allergic disease: In MCAS patients with a tryptase level of 8 ng/mL or greater, tryptase genotyping should be recommended.67,78 Finally, in symptomatic patients with a tryptase level greater than 15 ng/mL, the presence of HαT as well as the presence of the KIT mutation D816V should be tested for.78–80 This is important because patients who are suffering from SM, HαT, and an IgE-dependent allergy, have a high risk to develop MCAS.