Factors Related to UniTest PC, Greer Pick, and the Smallpox Needle

Reference: Allergy and Asthma Proceedings; January-February 2014; Harold S. Nelson et al.

Here are findings from the published work:

• Utilizing the three skin testing devices, twenty subjects were tested on the back, four sites with histamine and four sites with saline.
• Greer Pick produced 52% greater intrasubject variability than UniTest PC, and 46% greater than the smallpox needle.
• Wheals greater than 3 mm at saline sites occurred only from Greer Pick. There was no whealing greater than 3 mm at saline sites from either UniTest PC or the smallpox needle.
• The highest sensitivity (100%) was gained from UniTest PC while the lowest resulted from the smallpox needle (91%).
• Perception of pain was minimal for all three devices, but Greer Pick and the smallpox needle caused sharp pain while UniTest PC created a pressure-like pain.
• Technicians performing the skin tests considered UniTest PC the easiest to use of the three devices. They also observed that periodically a Greer Pick tine did not penetrate the epidermis, necessitating a repeat of the pricking.

In summary: UniTest PC was the only device that produced 100% sensitivity and 100% specificity. Pain from UniTest PC was defined as "pressure-like," while pain from Greer Pick and the smallpox needle was referred to as "sharp." Greer Pick produced 52% greater intrasubject variability than UniTest PC, and 46% greater than the smallpox needle. Technicians found UniTest PC easier to use than the other devices, and observed that periodically a Greer Pick point did not penetrate the epidermis, necessitating a repeat of the pricking.