A quantitative, non-invasive method for the characterization of flushing reactions.

A new method for the characterization of flushing reactions is established based on the curvilinear relationship between malar skin temperature and an index of cutaneous blood flow in the face. Previous studies relied on the absolute change in malar temperature which overlooks the curvilinear aspect of this relationship. The change in malar thermal circulation index (delta MTCI) is derived from the mathematical model of this curvilinear relationship. There were 71 positive flushing reactions in 162 challenges to a variety of agents. The peak malar temperature, change in malar temperature, and delta MTCI significantly correlated with flushing (p less than 0.001). For the commonly used threshold values for change in malar temperature of 1.1 degrees C and 1.2 degrees C, sensitivity was only 63.4 and 54.9, respectively. The sensitivity, specificity, and predictive value of a positive result for the delta MTCI were 90.1, 95.6 and 94.1, respectively. delta MTCI did not appear to be related to the baseline malar temperature, suggesting that a low malar temperature did not predispose to flushing. Thus, the inverse relationship between change in malar temperature and baseline malar temperature results solely from the curvilinear relationship between malar skin temperature and cutaneous blood flow in the face. Data from 2 previously reported studies are reevaluated employing the delta MTCI method; in both studies the new method is more sensitive without loss in specificity. The results indicate that delta MTCI may be useful as an accurate, noninvasive method for the quantitative characterization of flushing reactions.