Quantification of contact allergic inflammation: a comparison of existing methods with a scanning laser Doppler velocimeter.

Responses to a range of doses of common contact dermatitis-producing allergens were measured using a novel scanning laser Doppler velocimeter and three commonly used conventional measurement techniques. The techniques were compared in terms of sensitivity, measurement error, range of the linear portion of the dose-response curve and ease of use. The detection thresholds of the objective methods did not differ significantly and did not detect responses at concentrations less than those required to produce a visible response. Of the objective methods the range of linearity was greatest when reactions were measured using change in skin fold thickness, erythema or area of inflammation. Measurement error was greatest with measurements made using the conventional laser Doppler velocimeter. Present instrumental methods are no more sensitive than visual assessment in the reading of patch test reactions. The conventional laser Doppler velocimeter was least suited for measurement of allergic contact hypersensitivity reactions as readings are time-consuming, show detectable changes over a more limited range of allergen concentration, and have a larger measurement error than the other methods. There is no single best method for measuring allergic contact hypersensitivity reactions. Useful data over a wide range of allergen concentrations can best be obtained by measurement of skin fold thickness, erythema or area of reaction using the scanning laser Doppler velocimeter. The scanning laser Doppler velocimeter has the added advantages of being able to measure area of reaction without contact with the skin surface and to measure reactions at all skin sites.