The lancet weight determines wheal diameter in response to skin prick testing with histamine

BACKGROUND:Skin prick test (SPT) is a common test for diagnosing immunoglobulin E-mediated allergies. In clinical routine, technicalities, human errors or patient-related biases, occasionally results in suboptimal diagnosis of sensitization. OBJECTIVE:Although not previously assessed qualitatively, lancet weight is hypothesized to be important when performing SPT to minimize the frequency of false positives, false negatives, and unwanted discomfort. METHODS:Accurate weight-controlled SPT was performed on the volar forearms and backs of 20 healthy subjects. Four predetermined lancet weights were applied (25 g, 85 g, 135 g and 265 g) using two positive control histamine solutions (1 mg/mL and 10 mg/mL) and one negative control (saline). A total of 400 SPTs were conducted. The outcome parameters were: wheal size, neurogenic inflammation (measured by superficial blood perfusion), frequency of bleeding, and the lancet provoked pain response. RESULTS:The mean wheal diameter increased significantly as higher weights were applied to the SPT lancet, e.g. from 3.2 ± 0.28 mm at 25 g to 5.4 ± 1.7 mm at 265 g (p<0.01). Similarly, the frequency of bleeding, the provoked pain, and the neurogenic inflammatory response increased significantly. At 265 g saline evoked two wheal responses (/160 pricks) below 3 mm. CONCLUSION AND CLINICAL RELEVANCE:The applied weight of the lancet during the SPT-procedure is an important factor. Higher lancet weights precipitate significantly larger wheal reactions with potential diagnostic implications. This warrants additional research of the optimal lancet weight in relation to SPT-guidelines to improve the specificity and sensitivity of the procedure

Clinical course of rhinitis and changes in vivo and in vitro of allergic parameters in elderly patients: a long-term follow-up study.

Changes in rhinitis symptom severity tend to decrease with aging, but whether the decrease is associated with allergic skin test reactivity, serum total and specific IgE, and nasal eosinophils or determined only by aging is poorly understood. The aim of the study was to analyze sensitivity in vivo and in vitro some 15 years after primary testing, skin prick test (SPT), serum total and specific IgE, ratio sIgE/tIgE, and nasal eosinophils in order to evaluate changes due to age and changes due to the severity of rhinitis symptoms. One hundred and eight rhinitis patients who had been investigated in 1995 were re-interviewed and their current allergy re-assessed after a follow-up of 15 years. All patients were SPT with eight common allergens in the area of Palermo (Italy). Rhinitis symptoms tended, on average, to have become milder at the follow-up. All parameters examined showed a decreasing trend in older age groups over the period between the two investigations. Rhinitis symptoms tend to become milder and the allergic parameters both in vivo and in vitro usually decrease in the long run; however, the changes in rhinitis symptoms appear to be related to changes in the nasal eosinophils, independently of SPT and serum-specific IgE