Related Experiment Video
Updated: May 12, 2026
Minimal Erythema Dose (MED) Testing
Published on: May 28, 2013
Minimal phototoxic dose (MPD) measurements for topical photochemotherapy using a semiautomated MPD tester
D Al-Ismail1, C Edwards, O Al-Ofi
1Department of Dermatology, Aneurin Bevan Health Board, St Woolos Hospital, Newport, U.K.
Background:
The traditional method of assessing minimal phototoxic dose (MPD) prior to photochemotherapy with psoralen-ultraviolet A (PUVA) is inconvenient and cannot directly determine PUVA start doses. A handheld minimal erythema dose UVB tester can be modified by fitting a TL-10 UVA compact fluorescence lamp (CFL).
Objectives:
To determine whether MPD testing is possible with a CFL and to calculate a fixed factor to convert observed MPD to PUVA-equivalent MPD.
Methods:
Patients had two sets of MPD tests performed on symmetrical, contralateral sites on the lower back. MPD test results from a panel of PUVA lamps were compared with MPD from the modified handheld tester. Additionally, a questionnaire survey was completed by 43 U.K. phototherapy units to assess routine practice concerning MPD testing prior to PUVA therapy.
Results:
Thirty-seven patients with psoriasis were recruited. Boston phototypes in the 31 with conclusive MPD reactions were: I, four; II, 11; III, 12; and IV, four. The handheld MPD results were linearly related to the PUVA panel MPD results as follows: PUVA MPD = 0·48 × handheld MPD + 0·17 J cm(-2). The measured PUVA MPD was 0·48 of the handheld MPD, not 0·15 as predicted by the published PUVA action spectrum.
Conclusions:
The modified MPD tester is a convenient and safe method for PUVA MPD testing, overcoming many problems of the 'traditional method'. The difference between the PUVA and TL-10 lamps was lower than predicted from published studies. This suggests that formal re-evaluation of the erythema action spectrum for PUVA is now needed.
Insights
A modified handheld tester offers a convenient method for minimal phototoxic dose (MPD) testing before psoralen-ultraviolet A (PUVA) photochemotherapy. This new approach simplifies PUVA start dose determination, improving patient treatment protocols.
Area of Science:
- Dermatology
- Photobiology
- Medical Device Technology
Background:
- Traditional minimal phototoxic dose (MPD) assessment for psoralen-ultraviolet A (PUVA) photochemotherapy is cumbersome.
- Existing methods do not directly establish optimal PUVA starting doses.
- A modified handheld minimal erythema dose (MED) UVB tester with a TL-10 UVA compact fluorescence lamp (CFL) was investigated.
Purpose of the Study:
- To evaluate the feasibility of using a modified handheld tester for MPD determination.
- To establish a conversion factor for relating handheld tester results to PUVA-equivalent MPD.
- To assess current practices in MPD testing across UK phototherapy units.
Main Methods:
- Two sets of MPD tests were conducted on symmetrical skin sites in patients.
- MPD results from a standard PUVA lamp panel were compared with those from the modified handheld tester.
- A survey of 43 UK phototherapy units gathered data on routine MPD testing procedures.
Main Results:
- Thirty-seven patients with psoriasis participated; 31 had conclusive MPD reactions across Boston phototypes I-IV.
- A linear relationship was found: PUVA MPD = 0·48 × handheld MPD + 0·17 J cm(-2).
- The measured PUVA MPD was 0.48 times the handheld MPD, differing from the predicted 0.15 based on the established PUVA action spectrum.
Conclusions:
- The modified handheld tester provides a convenient and safe alternative for PUVA MPD testing, addressing limitations of traditional methods.
- Observed differences between PUVA and TL-10 lamps were smaller than anticipated from prior research.
- These findings indicate a need for re-evaluating the erythema action spectrum for PUVA therapy.
