The clinical manifestations of allergic diseases are often the same as other diseases, making their diagnosis difficult.
Therefore, clinicians often need a laboratory test capable of correctly identifying them.
Suppose the test combines low costs, execution speed, availability in most laboratories, and a high level of sensitivity to identify its target population. In that case, we have an excellent instrument for epidemiological studies of the prevalence of allergic diseases.
The Phadiatop has been used extensively as a respiratory allergy screening test.
In principle, Phadiatop is an in vitro test that allows the identification of individuals who are sensitive to multiple inhalant allergens simultaneously. To be a valuable and sensitive method, the Phadiatop must be made up of the most prevalent aeroallergens in the study area.
In Brazil, several different studies of selected allergic populations have also shown a high prevalence of sensitization to house dust mites: D. pteronyssinus, D. farinae, and Blomia tropicalis and, less frequently: animal epithelium, cockroach allergens and, more rarely fungi.
Depending on the population studied, the positivity rate for Phadiatop can vary. It will be lower among younger children or normal subjects and higher among patients with respiratory allergies.
Smith-Sivertsen et al. conducted a comparative study of the prevalence of allergic respiratory disease in two adult populations living in two different countries, Russia and Norway, but living in adjacent regions.
In addition to a specific questionnaire on symptoms, the Phadiatop was used as a screening test to identify sensitized individuals.
The authors reported that 20.7% of Norwegians and 25.7% of Russians were positive for Phadiatop. Tschopp et al. Phadiatop have seen the positivity in 29% of normal adults they tested. On the other hand, Williams et al. observed a positivity rate of 71.7% among patients with a clinical diagnosis of respiratory allergy.
The current study found that 67.6% of children with allergic diseases and 25.8% of those without allergies were positive when tested with Phadiatop.
The reduced positivity rate for Phadiatop among allergic children is the result of the fact that patients with non-respiratory manifestations were included in the calculation.
There was a 40% positivity level among babies with wheezing, and those with food allergies were 56% positive. These results are explained by young patients and the type of allergic disease, respectively.
However, the positivity for Phadiatop was high among patients with atopic dermatitis, that is, 82.1%.
Controversy exists about the role that mites play as aggravating or causative agents of atopic dermatitis. Furthermore, it is known that around 50% of these patients will progress to allergic respiratory disease.
Patients with atopic dermatitis and house dust mite-specific serum IgE show improvement when their environmental exposure to house dust mites is controlled. The positivity rate among patients with respiratory allergies was 77.3%, comparable to those observed by others.
Another use of an allergy diagnostic test would be its use as a predictive method for the subsequent development of allergic disease. Several different researchers studied the positivity of Phadiatop as a marker for allergic diseases, particularly respiratory diseases.
In a follow-up study from birth to five years, children at risk of developing asthma, the children of asthmatic parents, were evaluated with Phadiatop at six months, 18 months, and five years.
Of the children whose tests were positive at six months, 75% had manifested as asthmatic at 18 months, and all had done so at five years of age. This being the case, the authors found that Phadiatop had an 80% predictive value in predicting asthma in children at risk.
This value is significantly higher than the 53%, which would be the case if a positive aeroallergen skin test result had been included in the diagnostic criteria.
Kotaniemi-Syrjanen et al. studied Phadiatop as a predictive test for the development of asthma in infants less than two years old who had been hospitalized for acute wheezing.
Blood samples were taken at this point and stored until the children were at least five years old. They were then followed up to school age. They were then evaluated for asthma and other allergic manifestations, and serum IgE levels specific to inhalants and food allergens were analyzed.
Forty percent of the initial population progressed to asthma, and Phadiatop was positive in 18% of the entire group, and all of these patients became asthmatic.
In an attempt to identify risk factors for hospital admission and readmission due to acute exacerbations in children younger than four years with asthma, Wever-Hess et al. reported sensitization to aeroallergens (positive Phadiatop test) was associated with an eight-fold increased risk of recurrent exacerbations.
The question remains which of the many different screening methods used routinely is the most appropriate: history, immediate hypersensitivity skin tests, specific IgE serum analysis, or Phadiatop.
Williams et al. studied the value of Phadiatop as a diagnostic method for sensitization in allergic children and adolescents treated in specialized services. The results were compared with those of the skin tests of immediate hypersensitivity for aeroallergens, with specific IgE, and with medical history.
According to Williams et al., the medical history induced a false positive result in about 23% of the cases. Laboratory tests had a good correlation. Phadiatop was positive in 73.1% of those with positive skin tests, 71% of those with positive RAST, and 71.7% of all patients.
There was 99% agreement between positive Phadiatop patients with specific serum IgE tests and 98% agreement with positive immediate hypersensitivity skin tests, and 83.2% with positive clinical history. Levels of understanding were also high among those with negative Phadiatoptest.
Tschopp et al. studied the diagnostic value of the immediate hypersensitivity skin test, serum levels of total IgE, and Phadiatop in a Swiss adult population.
The prevalence of allergic asthma was 1.8%, and that of allergic rhinitis was 16.3%. The most positive Phadiatop results were 29% in the general population, and positivity was 23% for both skin tests and serum total IgE assays.
The sensitivity of Phadiatop for the diagnosis of allergic asthma was significantly higher than that of skin tests (72.5% x 65.4%), and the same occurred with allergic rhinitis (77.1% vs. 68.4%); both were better than serum IgE levels. However, the specificity and efficacy were better for the skin tests than for Phadiatop.
Although it was already known that Phadiatop is made up of inhalable allergens, no studies have been carried out in our country that has identified these allergens. This being the case, a comparative analysis of the positivity of Phadiatop and the various specific serum IgE tests for several different allergens was performed.
To confirm that food allergens were not included in Phadiatop, we had children with food allergies in the research. The highest levels of agreement were found with house dust mites: D. pteronyssinus, D farinae, and Blomia tropiclais.
Using the Phadiatop as a method to diagnose sensitization to each of the mites, we established their sensitivity, specificity, and positive and negative predictive values.
In conclusion, we have shown in this study that Phadiatop positivity is elevated among children with respiratory allergies and that house dust mites are the main components.