Standardization of the Prick Test

The different needles and methods used in the prick test give rise to disparate results. This has significance when carrying out multi-centre studies and when using the technique in the standardization of allergenic extracts. With test reliability as our objective, prick tests were carried out on 30 subjects: 10 patients sensitive to Dermatophagoides pteronyssinus received a glycerine extract of known allergenic potency, 10 healthy individuals 2.5% codeine phosphate in a glycerine solution, and another 10, histamine 1/1000. The total prick tests per individual was 27 with each of the needles employed (Allergy Pricker, the Morrow-Brown needle and Insulin needle in accordance with Pepy's procedure). The tests were carried out systematically by three different testers, and the total number of prick tests performed was 810. With the Allergy Pricker, no differences were observed among results obtained by the same tester, nor when the results of the three testers were compared. With the Morrow-Brown needle, the results varied in the same person and from one tester to another, and on many occasions the test was negative. With the Pepys method, no falsely negative results were obtained, but there was considerable variation in the size of the wheal. The variation coefficient is 41% with the Allergy Pricker, and 115% and 64% with the Morrow-Brown and Pepys method, respectively. In conclusion, the results obtained clearly indicate that the highest degree of reproducibility is obtained with the Allergy Pricker.