TMPRSS11D and Allergy: In sub-sequent studies, the upper limit of normal tryptase was reported to amount to 8.23 ng/mL,40 14 ng/mL,41 or 15 ng/mL.42–44,54 The different cut-off levels in these studies may be explained by a different statistical approach, by random variations in the fractions of HαT-positive individuals in these control cohorts, by age or ethnic factors, and/or by the fact that asymptomatic donors with a known allergy were either excluded or included in these analyses.