MEASUREMENT CRITERIA AND POSITIVE THRESHOLD OF THE DERMATOPHAGOIDES-PTERONYSSINUS PRICK TEST IN CHILDREN

In order to define the best threshold of a positive result to the prick test (pr-t) to Dermatophagoides Pteronyssinus (DP), results of the DP pr-t in 80 children allergic to DP were compared with those of 22 control children. The allergic group was defined on the basis of a recent asthma attack, raised total serum IgE and a positive intradermal reaction (idr). Four pr-t measurement criteria were used : papule diameter (D1), the difference between D1 and the negative control (-) (D2), the ratio between D1 and the positive control (+) (D3) and the ratio between D2 and the difference with controls (D4). Means of + (9 % codeine phosphate) and - controls were significantly greater in the controls than in the allergic group, while mean figures for D1, D2, D3 and D4 were significantly greater in the latter. In the allergic group, there was a significant difference between idr on the one hand and D1, D2 and D3 on the other hand. The most discriminative positive thresholds for DP pr-t were D4 greater-than-or-equal-to 0.25, D2 greater-than-or-equal-to 1 mm, D3 greater-than-or-equal-to 0.70 and D1 greater-than-or-equal-to 5 mm. Nine allergic patients had a pr-t reaction less than the 4 values chosen as thresholds (poor responders). They were compared with the 54 allergy sufferers in whom the pr-t response was above the 4 threshold values (good responders). Absence of response to pr-t was not due to cutaneous hyporeactivity since the + controls and - controls did not differ from those of the good responders, despite the relatively young age of the subjects. The chief cause of a negative pr-t appeared to be less sensitisation, as reflected by the significant difference between the idr of good and poor responders. In total, these results lead to the suggestion of the following as positive thresholds for DP pr-t : Probable allergy: papule diameter greater-than-or-equal-to 5 mm or ratio of papule diameter over that of the + control greater-than-or-equal-to 70 %. In both cases, the papule diameter should also exceed that of the negative control by at least 2 mm. Virtually certain allergy: papule diameter greater-than-or-equal-to 6 mm or greater than that of the + control. In both cases, it should also exceed that of the negative control by at least 3 mm.