Sampson H A, Ho D G
Johns Hopkins University School of Medicine, Baltimore, MD 21287-3923, USA.
J Allergy Clin Immunol. 1997 Oct;100(4):444-51. doi: 10.1016/s0091-6749(97)70133-7.
The double-blind, placebo-controlled food challenge (DBPCFC) is the "gold standard" for diagnosis of food hypersensitivity. Skin prick tests and RASTs are sensitive indicators of food-specific IgE antibodies but poor predictors of clinical reactivity. Previous studies suggested that high concentrations of food-specific IgE antibody were predictive of food-induced clinical symptoms. Because the CAP System FEIA (Pharmacia Diagnostics, Uppsala, Sweden) provides a quantitative assessment of allergen-specific IgE antibody, this study was undertaken to determine the potential utility of the CAP System FEIA in diagnosis of IgE-mediated food hypersensitivity.
Sera from 196 patients with food allergy were analyzed for specific IgE antibodies to egg, milk, peanut, soy, wheat, and fish by CAP System FEIA. Sera were randomly selected from 300 stored samples of children and adolescents who had been evaluated by history, skin prick tests, and DBPCFCs. The study population was highly atopic; all patients had atopic dermatitis, and approximately 50% had asthma and allergic rhinitis at the time of initial evaluation. The performance characteristics of the CAP System FEIA were compared with those of skin prick tests and the outcome of DBPCFCs or "convincing" histories of anaphylactic reactions.
The prevalence of specific food allergies in the study population varied from 22% for wheat to 73% for egg. Allergy to egg, milk, peanut, and soy accounted for 87% of confirmed reactions. The performance characteristics of skin prick tests and CAP System FEIA (egg, milk, peanut, fish) were comparable, with excellent sensitivity and negative predictive accuracy but poor specificity and positive predictive accuracy. The performance characteristics of the CAP System FEIA for soy and wheat were poor. For egg, milk, peanut, and fish allergy, diagnostic levels of IgE, which could predict clinical reactivity in this population with greater than 95% certainty, were identified: egg, 6 kilounits of allergen-specific IgE per liter (kU[A]/L); milk, 32 kU(A)/L; peanut, 15 kU(A)/L; and fish, 20 kU(A)/L.
When compared with the outcome of DBPCFCs, results of CAP System FEIA are generally comparable to those of skin prick tests in predicting symptomatic food hypersensitivity. Furthermore, by measuring the concentrations of food-specific IgE antibodies with the CAP System FEIA, it is possible to identify a subset of patients who are highly likely (>95%) to experience clinical reactions to egg, milk, peanut, or fish. This could eliminate the need to perform DBPCFCs in a significant number of patients suspected of having IgE-mediated food allergy.
双盲、安慰剂对照食物激发试验（DBPCFC）是诊断食物过敏的“金标准”。皮肤点刺试验和放射性变应原吸附试验（RAST）是食物特异性IgE抗体的敏感指标，但对临床反应性的预测能力较差。既往研究表明，高浓度的食物特异性IgE抗体可预测食物诱发的临床症状。由于CAP系统荧光酶免疫分析（FEIA）（瑞典乌普萨拉法玛西亚诊断公司）可对过敏原特异性IgE抗体进行定量评估，因此本研究旨在确定CAP系统FEIA在诊断IgE介导的食物过敏中的潜在效用。
采用CAP系统FEIA分析196例食物过敏患者血清中针对鸡蛋、牛奶、花生、大豆、小麦和鱼类的特异性IgE抗体。血清是从300份储存的儿童和青少年样本中随机选取的，这些样本均经过病史、皮肤点刺试验和DBPCFC评估。研究人群具有高度特应性；所有患者均患有特应性皮炎，约50%的患者在初次评估时有哮喘和过敏性鼻炎。将CAP系统FEIA的性能特征与皮肤点刺试验以及DBPCFC的结果或过敏反应的“明确”病史进行比较。
研究人群中特异性食物过敏的患病率从小麦的22%到鸡蛋的73%不等。对鸡蛋、牛奶、花生和大豆的过敏占确诊反应的87%。皮肤点刺试验和CAP系统FEIA（针对鸡蛋、牛奶、花生、鱼类）的性能特征相当，具有出色的敏感性和阴性预测准确性，但特异性和阳性预测准确性较差。CAP系统FEIA对大豆和小麦的性能特征较差。对于鸡蛋、牛奶、花生和鱼类过敏，确定了能够以大于95%的确定性预测该人群临床反应性的IgE诊断水平：鸡蛋，每升6千单位过敏原特异性IgE（kU[A]/L）；牛奶，32 kU(A)/L；花生，15 kU(A)/L；鱼类，20 kU(A)/L。
与DBPCFC的结果相比，CAP系统FEIA的结果在预测有症状的食物过敏方面通常与皮肤点刺试验的结果相当。此外，通过使用CAP系统FEIA测量食物特异性IgE抗体的浓度，可以识别出极有可能（>95%）对鸡蛋、牛奶、花生或鱼类发生临床反应的一部分患者。这可以使大量疑似IgE介导食物过敏的患者无需进行DBPCFC。
