A comparison of narrowband (TL-01) UVB-induced erythemal response at different body sites

In most dermatology centres where phototesting is performed, the starting dose is calculated as a proportion of the minimal erythema dose (MED). Previous studies have found significant differences in MED readings between forearm and back skin with both broadband and narrowband (NB) UVB. Our objective was to compare MEDs obtained from three body sites, the forearm, back and abdomen, to see if there was a significant difference in individuals. We recruited 20 healthy volunteers who were exposed to our standard dose series for phototesting with NB-UVB to three body sites: forearm, back and abdomen. MEDs were assessed 24 h post exposure. The median MED for the abdomen was 0.79 J/cm2, the back 0.95 J/cm2 and the arm 1.11 J/cm2. Friedman's analysis of variance by ranks showed that these differences were significant (P = 0.003). There was no correlation between skin type and MED for any of the three anatomical sites. Our results support phototesting for all patients prior to treatment with NB-UVB. Furthermore, we have shown that the abdomen is the anatomical site of choice for phototesting, as this will result in a reduced risk of burning episodes.