Allergy skin prick reactions change with lancet weight

Allergy reactions of the acute (immediate) hypersensitivity type mediated by IgE immunoglobulins are commonly tested by skin prick testing (SPT) with suspect antigens. Research just published in PLOS One reveals that differences in lancet weight add to the factors that can cause diagnostic inaccuracy. The authors state:

"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...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."

They conducted SPT for allergy on subjects by applying solutions of histamine (1 mg/mL and 10 mg/mL) and one control solution (saline) with lancets of four different weights (25 g, 85 g, 135 g and 265 g) and observed wheal size, neurogenic inflammation, bleeding, and pain response.

Apparent allergy reactions with greater lancet weight

They found that differences in lancet weight can be a significantly misleading factor in the diagnosis of IgE allergy.

"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."

Clinicians should bear this in mind when analyzing SPT results, especially when they are confounding or otherwise in question. The authors conclude:

"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."