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Table 3 Technical procedure for SPT

From: Guidelines for the use and interpretation of diagnostic methods in adult food allergy

Apply one drop for each allergen extract to be tested, maintaining a minimum distance of 3 cm between drops on the volar part of the patient’s forearm (5 cm from wrist and 3 cm from the antecubital fossa)
Apply pressure, through a sterile, disposable lancet, to each single allergen, pricking to a depth of 1 mm for each drop, perpendicular to the skin’s surface
Hold for about 3 s with moderate pressure without moving the hand or turning to avoid bleeding
Carefully remove the allergen solution with blotting paper
 The same procedure is to be followed to test histamine (10 mg/ml) as a positive control and physiological glycerine as a negative control
Reading of the results: after 15 min from the performance of the test
Interpretation of the test: a positive result is defined by the appearance of a wheal of at least 3 mm in average diameter. Responses to histamine and the negative control should be carefully considered. The latter verifies that the patient does not suffer from dermographism and the former demonstrates a “normal response” to histamine (with no negative interference from drugs or other conditions, such as hypo-reactivity of the skin)