Food Atopy Patch Test And The Study Of Its Methodology

BackgroundAtopy patch test (APT) is a relatively new allergens detection method in clinical research stage, which can be used to detect delayed-type hypersensitivity induced by inhaled allergens, food allergens and help patients to clear relevant allergens. About 40.8% children with atopic dermatitis (AD) accompany with food allergy, for patients with delayed-type hypersensitivity more helpful to the patients of AD with chronic, recurrent dermatitis as clinical manifestations, specialiy for patients with food allergy. Different with antigen of inhaled allergens, once clear-cut the food allergen, it is possible to relieve illness or reduce the recurrence of the disease by avoid food allergens and adjust the diet structure. APT for food allergens are conducted according to the EAACI scheme, so there is no standardized antigen yet and fresh food is recommended. But there may be difference of food in component, character and concentration, which possibly act as factors to interfere the reaction of APT. Another difficulty for APT lies in the subjectivity and instability of reading. Reading is different from patch test, because of its special reaction kinetics, and the use of fresh food may increase the nonspecific response, so it is important to distinguish stimulus response and positive response. Therefore suitable objective indicators are needed for the reliability of reading. Laser Doppler perfusion imaging can be used to detect the microcirculation blood flow of local skin, which can objectively reflect the degree of erythema and dynamically reflect the degree of erythema change and blood flow in corresponding sites, In our study, it is applied to the evaluation of APT response and discussion of its relationship with response.ObjectiveEvaluate the response characteristics of APT for common food allergen in patients with atopic dermatitis, and investigate the methodology for ATP.MethodThe first session:95 questionnaires are carried out for the patients with AD and their medical information, food allergy and food avoidance. We select common food allergens, meanwhile conducting APT and SPT. Then we compare the both result and analyze its consistency. Then we analyze the relationship between positive reaction rate and age, the dry degree of skin, classification, the severity of patient’s condition and total IgE, and analyze the characteristics of APT positive response.The second session:31 health volunteer was recruited in our study. And tape paste was conducted on the marked area to simulate impaired skin barrier. Measuring the TEWL, CAP before and after tape paste and evaluate the degree of skin damage. Eggs were tested as antigen in different component and different concentration on pasted area; shrimps with different character were conducted patch test on the area without paste, and the occlusion time for the left and right back was 24h and 48h respectively with random distribution. Results were read 30 min,24 h and 48h after removal of the chamber and analyze the difference between various test factors. And using real-time video monitoring system to detect the skin blood flow on the reaction area and evaluate its role in food APT.ResultsThe first session:the positive rate of food APT were significantly higher than SPT, there were no consistency between the two tests except eggs. Except eggs, soybean, beef, the APT positive rate of other food with age distribution of patients, the APT positive rate of total food and different degree of drying, mixed AD and simple AD has no statistically significant differenceCP>0.05). Except peanut, there was no statistically significant difference of APT positive rate between different severity of illness(P>0.05). Compared the response of 0.5h, there was no increased trend in 24h. The second session:1.The TEWL, CAP and T/C significant increased before and after tape paste the skin.2. The positive response with the antigen of yolk and shrimp increase with the time extension of occlusion (P<0.05).The same occlusion time, the response of egg yolk was stronger than egg white and higher in blood flow and its variation (P<0.05).3. The response intensity was positive correlation with blood flow volum (P<0.05). The results of 0.5h,24h reading time and overall reaction were positive correlation with the corresponding blood flow volume(P<0.05). And the blood flow volume of positive response were higher than stimulus response only in 0.5h period (P<0.05). Total response compared with blood flow volume, there was statistical significance (P<0.05) between the blood flow volume in each period and the difference between positive and negative response, negative response and stimulus response, positive response and stimulus response, except in the 48h period of 24h occlusion. The blood flow volum of the positive response in 0.5h and 24h period were higher than questionable response(P<0.05). The blood flow volum and its variation of total response in 0.5h and 24h between questionable response and positive response had statistical significance(P<0.05).ConclusionMost patients with AD conducted food avoidance in daily diet, but only small part was effective. The positive rate of APT in AD patients was higher than SPT, and the positive rate of part antigen were influenced by age. But there were better stability in different severity of patient’s condition and the degree of drying, and no relation with accompanying suction system atopic disease and the increase of total IgE. There was no ’crescendo’ phenomenon in the positive reaction of food APT, so the advanced reaction kinetics characteristics cannot be helpful to the reading. When the barrier was impaired, there was no significantly increase in the positive response of eggs. Egg white and egg yolk belongs to the two parts of the same substance and the reactions were different, suggest that the APT should carry out separately. The positive response of APT was not influenced by the concentration of antigen. Blood flow volume can be used to classify the stimulus response and positive response, the questionable and positive response. Therefore, the noninvasive detection for blood flow volume may offer an effective and objective method for the reading of APT, promoting the reliability of reading and as a subsidiary method for reading.