PD21 Investigating the role of narrowband ultraviolet B phototesting in general dermatology

Abstract

Narrowband ultraviolet B (NB-UVB) light sources have an established role in phototherapy. They are widely available in general dermatology but can also be utilized for phototesting. Aiming to improve phototesting accessibility, we investigated the accuracy and reliability of NB-UVB minimal erythema dose (MED) compared with the 305 ± 5-nm monochromator MED as determined in the tertiary photobiology service. Ethics approval was obtained (CALDICOTT-2025-256) and patients’ data were collected from an in-house database and analysed by two members of the research team using Microsoft Excel. Duplicates and return visits were removed, so data from 513 individual patients were included. Abnormal NB-UVB photosensitivity was defined as MED < 82 mJ cm−2. Abnormal 305 ± 5-nm photosensitivity was defined as MED < 33 mJ cm−2. NB-UVB MED testing had a specificity of 96% and sensitivity of 64%. The kappa (κ) score between NB-UVB and 305 ± 5 nm was 0.65, indicating substantial agreement, but the false negative rate of 36% makes it unsuitable in undifferentiated patients. Subgroup analysis investigated the sensitivity of NB-UVB MED in different conditions. The NB-UVB MED was shown to be useful in diagnosing chronic actinic dermatitis (CAD) (n = 99): specificity 79%, sensitivity 84%, κ = 0.47. It was not useful in poly­morphic light eruption (n = 147): specificity 96%, sensitivity 8%, κ = 0.05. The NB-UVB MED was not helpful in diagnosing solar urticaria according to our small patient cohort (n = 34), with only 38% sensitivity despite 100% specificity. Overall, the findings of this study demonstrate that NB-UVB MED testing has an effective role in phototesting, especially the unique suitability of the NB-UVB lamp in diagnosing patients with CAD. It is important to be able to identify CAD using NB-UVB MED testing, as the condition can be clinically indistinguishable from photoaggravated atopic dermatitis. NB-UVB phototherapy is available in most secondary dermatology centres. We therefore recommend that NB-UVB MED testing is an accessible safety measure to detect abnormal CAD photosensitivity.