Diagnostic Decision Points of Specific IgE Titers in Patients With Food Allergy: Are They Appropriate in All Clinical Settings?

In daily clinical practice, it is not so easy to make a confirma-tive diagnosis of food allergy. Interpretation of skin prick test and serum food-specific IgE (sIgE) test results is influenced by detailed clinical history of an individual patient, but ingested foods which provoke adverse reactions often contain many ingredients and lead to a misdiagnosis of food allergy. Oral food challenge is recommended for the diagnosis of food allergy, but we cannot always perform oral food challenge for various reasons , including recent severe reactions to food, severe atopic dermatitis, patient' and/or parents' refusal and noncooperation of young patients. Thus, from the physician's point of view, cutoff values of sIgE titers that provide high positive and negative predictive values would be very useful in clinical settings because they help determine which patient is more likely to have symptoms in response to a certain food and which are probably nonreactive. Since Sampson 1,2 was first to publish studies on the efficacy of serum specific IgE in determining which food-allergic patient is more likely to fail oral food challenge, 3 their diagnostic decision points (DDPs) have been widely used in clinical practice worldwide as well as in Korea. 4 Positive predictive value (PPV) represents the proportion of symptomatic individuals to those with positive test results. 5 Positive predictive accuracy can be calculated by the following equation: Positive predictive accuracy = sP / sP + (1 – f)(1 – P) where s=sensitivity, f=specificity, and P=prevalence of the condition in the population studied. 2 The composition of the population investigated affects the positive predictive accuracy as denoted in the formula. Predictive accuracy is difficult to establish because it varies with the prevalence of disease. 2 Samp-son et al. 2 attempted to minimize the influence of disease prevalence on DDPs among different populations and established DDPs from 90% specificity as an alternative approach. However , the value of the PPV was very low (50.0% in children <24 months of age and 59.3% in those ≥24 months of age, respectively) when the previously established DDPs of egg white-sIgE concentrations for egg allergy were applied in that study population ; the value of the PPV was slightly lower than 95% (83.3% in children <24 months of age and 91.7% in those ≥24 months of age, respectively) when the previously established DDPs of cow milk-sIgE concentrations for milk allergy was applied in this study population. 6 Similar results …