- For MAST, the test results show the level of specific IgE for each allergen, and a normal negative range is 0.000–0.349 IU/mL. SPT was described as negative (0, no reaction), 1+ (reaction greater than control reaction but smaller than half the size of histamine), 2+ (equal to or more than half the size of histamine), 3+ (equal to or more than the size of histamine) and 4+ (equal to or more than twice the size of histamine). The minimum size of a positive reaction is 3 mm
