Comparison between visual score and erythema index (DermaSpectrometer) in evaluation of allergic patch tests

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During the last decade several new bioengineering methods have been proposed for evaluation of patch test reactions in a more objective manner. The aim of the present study was to investigate the usefulness of erythema index (DermaSpectrometer) in a clinical setting, i.e., reading of allergic patch tests.


Twenty patients with known allergy to formaldehyde participated in the study. Each patient had patch tests for 2 days with formaldehyde solutions from 0 to 10,000 p.p.m. applied. Clinical reading of the test sites and measurement of the erythema index by the DermaSpectrometer were done 24 h after removal. A control group of 20 volunteers with no allergy to formaldehyde were tested in a similar way.


Erythema indices were significantly higher for visually rated positive patch tests than for negative tests (P<0.05). The single categories of visually positive reactions (+?, +, ++, +++) could not be unambiguously separated by the DermaSpectrometer. The correlation between clinical readings and the formaldehyde concentration (Spearman's rank correlation coefficient, r=0.60) was higher than between DermaSpectrometer readings and the formaldehyde concentration (r=0.35).


In a dilution series of formaldehyde patch testing, readings from a DermaSpectrometer were not found to give better information than visual readings.

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