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

The Lancet Weight Determines Wheal Diameter in Response to Skin Prick Testing with Histamine - Fig 2

<p><b>A)</b> The mean wheal diameters on the forearms for each lancet weight; 25 g, 85 g, 135 g and 265 g. A higher lancet weight significantly increased the sizes of the wheal reactions. <b>B)</b> The mean wheal diameters on the back for each lancet weight; 25 g, 85 g, 135 g and 265 g. A higher lancet weight significantly increased the sizes of the wheal reactions. A significant difference was also observed when comparing the two histamine concentrations: 1 mg/mL and 10 mg/mL. For each condition; n = 20. * = p < 0.05, ** = p < 0.01. Mean ± SEM.</p

The mean and coefficient of variation (CV %), calculated as the ratio between the standard deviation and the mean for the four predetermined peak lancet weights; 25 g, 85 g, 135 g and 265 g at the forearm and back.

<p>Data for applied lancet weight are pooled for conditions with saline, 1 mg/mL of histamine and 10 mg/mL of histamine. Notice that the deviation is proportionally higher in the 25 g weight group.</p

Weighted SPT lancet device.

<p>Depicts a suggested mechanical approach to a locked weight device allowing for SPT within a specific predetermined weight.</p