Precision Implementation of Minimal Erythema Dose (MED) Testing to Assess Individual Variation in Human Inflammatory Response

Minimal erythema dose testing, or MED testing, is a technique with a long history in dermatological and clinical phototherapy settings. And it’s primarily used to determine the smallest amount of radiation required to produce erythema, or visible reddening on the surface of the skin. In this particular study, what we’ve done is develop several new techniques and procedures that allow MED testing to be adapted for somewhat different purpose, which is to precisely quantify variation in human inflammatory activation.

The main advantage of precision dosing and measurement in MED testing pertains to the reproducibility of results, which then opens up new possibilities for systematically examining other factors that could be related to inflammation. Demonstrating the procedure will be two PhD students from my lab, Holly Sullivan-Toole and Corinne Carlton. Begin by escorting the participant to the testing room.

Explain the MED testing procedure to the participant and confirm understanding. Place cuff one on the non-dominant forearm. Remove only the protective wax paper backing from the lateral, not central, portions of the cuff.

After situating cuff one at the intended exposure site, place landmarks using a permanent marker to ensure that cuff two will be situated at precisely the same location. Then, mark the skin at four points outside of the creases of each of the side flaps of cuff one, the upper right, upper left, lower right, and lower left points. Ensure the marks are dark enough to last for 24 hours, so they may be used to place cuff three in precisely the same location at the follow-up appointment.

Next, use a calibrated spectrophotometer to record readings at each of the six open apertures in sequence. Ensure that the spectrophotometer is placed in the center of the cuff apertures, while avoiding moles, scars, or other blemishes to the extent possible. Finally, permanently record all SCI values.

To ensure consistent readings with the same calibration point, keep the spectrophotometer in the on position for the duration of the MED procedure and do not turn off until the post-exposure readings have been completed. After removal of cuff one, situate cuff two at the same location using the landmarks drawn on the skin for cuff one. Put on the necessary safety equipment, including UV-proof glasses, sleeves, and gloves, and make sure the participant does the same.

Prior to activating the lamp, arrange the participant’s arm such that the UV rays from the lamp will be perpendicular to the angle of cuff two on the participant’s arm. Briefly activate the lamp to adjust the distance to cuff two until the radiometer sensor reads 270 microwatts per centimeter squared. Next, place the radiometer sensor facing the UV lamp, parallel to the surface of the skin, and as close as possible to the location of cuff two.

Then, remove the first aperture covering before activating the UV source. Remove each window in the dose testing patch according to the schedule displayed here, which illustrates separate dosage schedules depending on the participant’s Fitzpatrick Skin Type. Activate the UV source and the stopwatch simultaneously, and remove each aperture covering on cuff two according to the correct dosage schedule, which is based on Fitzpatrick Skin Type.

Next, turn off the lamp at the precise time specified by the dosage schedule. Do not deactivate the stopwatch, as an additional series of spectrophotometer readings should be gathered exactly seven minutes subsequent to deactivation of the lamp, as described below. Lastly, after exactly seven minutes have passed since the deactivation of the lamp, record the final spectrophotometer readings from each aperture in cuff two.

Begin by calibrating the spectrophotometer in preparation for the follow-up appointment, 24 hours later. Prepare cuff three by removing all of the aperture coverings and leaving the white wax paper backing on the central portion of the patch. When placing cuff three on the participant’s arm, remove the white wax paper backing from the two side flaps of the patch.

Use the landmarks on the participant’s forearm to place cuff three in the same location as the previous two patches. Finally, take a reading at each of the six open apertures in sequence. These results show an accurate skin response to MED testing.

Here are complete data for a single representative subject, broken down by assessment period. Pre-exposure, seven minutes post exposure, and 24 hours follow-up. Each aperture, two through six, receives 25%more energy than the one before it.

Further, all 72 subjects are shown, indicating the variation that are likely to be encountered, across different FSTs. Perhaps the most important aspects of precision MED testing relate to the adherence to the proper dosage schedule for the identified Fitzpatrick Skin Type and also consistently maintaining the correct distance between the surface of the skin and the UV light source. Part of our motivation in developing these techniques is to facilitate future research examining how inflammatory responses could relate to any number of potentially interesting variables, such as psychological, pharmacological, or health-related factors.