A Rapid and Cost-Effective Device for Testing Minimal Erythema Dose

Abstract

Introduction: We describe a novel device for rapid and economical minimal erythema dose testing in patients undergoing ultraviolet (UV) light phototherapy for treatment of skin diseases. Methods: A minimal erythema testing device was designed and created using transparent plastic sheeting and printed patterns with increasing ink density, allowing for graded UV transmission of 100%, 80%, 60%, 40%, 20%, and 10% energy through six 10-mm square apertures. The plastic sheet was placed in a UV-impenetrable and Velcro-fitted adjustable sleeve, designed to fit easily onto a patient’s arm. A pilot validation study was performed, comparing this device with a commercially available windowed device in which the dose is controlled by varying the UV exposure time through sequential opening of each window. The pilot was conducted on healthy skin of two human subjects with different Fitzpatrick skin types. Results: In our subjects, tested with one device on each forearm, the minimal erythema dose (MED), judged visually, was identical. However, the test device allowed MED testing in 3 min compared with 15 min for the traditional device. The test device is equally effective for use with ultraviolet-A (UVA), narrowband ultraviolet-B (NB-UVB) and broadband ultraviolet-B (BB-UVB) wavelengths. The test device is economical, with manufacturing cost of less than US $2. Conclusion: We designed an MED testing device that is quick, accurate, cost-effective, and easy to use in the setting of a busy phototherapy practice. This device therefore has many advantages over existing MED testing approaches.