The diagnostic value of skin-prick tests in dermographic individuals

Fifty-five patients displaying significant dermographic wheals, who presented with respiratory or food allergy symptoms, were investigated prospectively. Fifty-five additional patients presenting with similar clinical histories as the study group but without dermographism were used as controls. Total serum IgE and skin-prick tests (SPT) to 30 common allergens were performed on all subjects. Specific IgE (RAST) was determined only in those whose history did not correlate with the skin-test results. Allergens that gave a positive reaction were retested with extra care to exert minimal pressure. No statistically significant difference was found in the percentage of positive SPT reactors when comparing dermographic patients and controls (chi 2 test). No significant difference was found when the number of positive SPT (mean values) was compared between dermographic subjects and controls (t-test). However, when the values of mild positive SPT (1+ to 2+) were compared between the two groups, there was a significant difference only on the first performance of SPT in dermographic individuals (P less than 0.05, t-test). Our findings demonstrate that SPT can be reliable even in the presence of dermographism. False positive results are occasionally observed when the reactions are mild, but careful repetition of positive SPT might eliminate this problem.