PD03 Normal erythema ranges in diagnostic phototesting

Abstract In diagnostic phototesting there are only a few published reference ranges for nonphotosensitive populations. These ranges are specific to the population being investigated and are dependent upon the equipment used. We wished to explore whether an equipment independent reference range could be produced expressed in units of standard erythema dose (SED). Two sources of data were used in this investigation. Firstly, data were obtained from narrowband ultraviolet B (311 ± 1-nm peak, TL01 lamp) phototherapy minimal erythema dose (MED) testing between 2020 and 2024 on patients with Fitzpatrick skin phototype I–III (n = 851), excluding photosensitivity conditions and repeat testing. Data are presented as the 2.5th to 97.5th percentile (95% reference range). Secondly, data were retrieved from a mono­chromator nonphotosensitive population reference range study performed in 2009. Fifty volunteers (skin phototype I–III) were irradiated and the reference range was calculated using bootstrapping to derive the 99% confidence interval around each end of the 95% reference range. All data were converted from units of mJ cm−2 to units of SED. The results are shown in the Table. The reference range in SED is similar across all the wavelengths delivered. The exception is at 335 ± 27 nm (half maximum bandwidth). These wavelengths are at a part of the erythema action spectrum (EAS) where there is a steep change in erythemal sensitivity. Expressing nonphotosensitive reference ranges in SED shows small variation between wavebands. The EAS was not a perfect match in the volunteer population, particularly at 335 ± 27 nm. While it may be useful to report photosensitive patient results in terms of SED, it remains important to also report results in terms of mJ cm−2, as abnormal photosensitivity conditions do not all follow the standard erythema curve (that is, the abnormal reactions can be quite different from ‘standard’ sunburn erythema). Our results suggest that a reference range expressed in SED is reasonably independent of wavelength, and therefore equipment. This may allow other photodiagnostic centres to utilize this range, but only if they have a similar background test population. However, these findings provide a significant step forward in attempting to introduce more consensus practice between photodiagnostic units in the UK and also have potentially broader application beyond.TableReference ranges in mJ cm−2 and standard erythema dose (SED) by wavelengthWavelength ± bandwidth at FWHM (nm)Reference range (mJ cm−2)Reference range (SED)295 ± 56.8–220.74–2.30300 ± 512–480.71–2.77305 ± 533–1200.66–2.58311 ± 1 (TL01)70–3930.44–2.46335 ± 273900–22 0001.01–5.3365 ± 2718 000–68 0000.73–2.84400 ± 2756 000 to > 82 0000.75 to > [1.58FWHM, full width at half maximum (half maximum bandwidth).