Evaluation of skin prick test sensitivity for 37 allergen extracts in atopic patients with nasal polyposis

Background Skin prick test (SPT) is a gold standard test for diagnosis of allergic [immunoglobulin E (IgE)] diseases. There is a subset of patients who have positive nasal provocation to allergens, despite having a negative SPT. The aim of our study was to evaluate SPT sensitivity in atopic patients with allergic nasal polyposis. We chose 56 patients (discussion with the patients regarding the benefits and hazards of the study was performed and informed consent was taken from them) with bilateral nasal polyposis (as diagnosed by full history taking, clinical examination, nasal endoscopic examination, and sinonasal computed tomography) who proved to be allergic (by full history taking, clinical examination, positive serum total IgE, serum-specific IgE, and tissue-specific IgE). SPT was performed using a panel of 37 allergen extracts. Results A total of 15 patients showed negative results to SPT representing 26.8%. In all, 41 patients showed positive results to SPT (73.2%); six patients (14.6%) showed positive result to only one allergen (monosensitized), whereas the remaining patients were polysensitized. The most common allergens found to be positive by SPT were: ′House Dust′ with positive results in 19 patients representing 46.3% of patients with positive results to SPT (41 patients), followed by ′Pollens′ with positive results in 18 patients (43.9%), ′House Dust Mite′ with positive results in 17 patients (41.5%), and then ′Molds′ with positive results in 14 patients (34.2%). Conclusion Negative SPT does not exclude allergy in atopic patients with nasal polyposis. Thus, before delivering a diagnosis of nonallergic rhinitis in patients with negative SPT to common allergen, further tests are needed. We recommend further studies to evaluate the prevalence, immunopathology, and management of local allergic rhinitis.


Introduction
Skin prick testing (SPT) is an essential test procedure to confi rm sensitization in immunoglobulin E (IgE)mediated diseases such as asthma, rhinoconjunctivitis, eczema, and anaphylaxis [1]. Worldwide, allergic rhinitis aff ects between 10 and 30% of the population, and sensitization (IgE antibodies) to foreign proteins in the environment is present in up to 40% of the population [2].
SPT is simple, quick, and is regarded as a gold standard method for allergy diagnosis [3]. Th e results of this test correlate with those of nasal challenge and bronchial challenge, which can also be used as surrogate tests to test clinically relevant sensitization [1].
Alvares et al. [4] studied a subset of patients who had positive nasal provocation to allergens, despite having a negative SPT. Th ey hypothesized that these patients have localized allergic rhinitis. Th ey found that the prevalence varies greatly, ranging from 0 to 100% of skin test-negative individuals. Th is wide range in prevalence is likely related to diff erences in methodology, including diff erences in allergen manufacturers, concentrations, and numbers of allergens tested and, perhaps most importantly, criteria for a positive nasal challenge [4].

Aim of the study
Th e aim of the study was to evaluate SPT sensitivity in atopic patients with nasal polyposis.

Patients and methods
(1) Th is study was a cross-sectional descriptive study.
It was conducted in both ENT

Patients
A total of 56 patients with bilateral nasal polyposis (consents: discussion with the patients regarding the benefi ts and hazards of the study was performed and informed consent was taken from them) were enrolled in the study after informed consent about the research and the procedures was taken.
All patients were subjected to the following: Full allergy history especially exposure to allergens and its association with clinical presentation and ENT history taking and clinical examination including SNOT-22 sinonasal outcome test-22 Questionnaire [5], nasal endoscopy, nonenhanced PNS-CT [6], and the diagnostic allergic workup, which included the following tests.

Skin prick test
Th e panel for skin testing was composed of histamine and saline, in addition to 37 diff erent allergen extracts for both inhaled and ingested allergens. Th e panel of allergen extracts were prepared in allergen extract unit, Department Of Allergy And Immunology, Ain-Shams University Hospitals. Th ey were prepared by aqueous vaccine method (weight/volume) [7] (Table 1).
A drop of solution of each test allergen was placed on the fl exor surface of the forearm, and a midpoint was used to prick the skin. SPTs were read at 20 min. Th e reaction to a SPT was considered positive if the wheal area caused by allergen was greater than 3 mm in diameter.

Serum total IgE level
Enzyme-linked immunosorbent assay was used for the quantitative determination of IgE concentration in human serum (BioChech IgE Enzyme Immunoassay; BioCheck Inc., Foster City, California, USA) [8].
Th e total IgE level in a normal, allergy-free adult is less than 100 IU/ml of serum. Th e minimum detectable concentration of IgE by this assay is estimated to be 5.0 IU/ml.
Interpretation of results was performed using multiallergen discs; results of at least 0.35 IU/ml was considered positive.

Tissue-specifi c IgE
Tissue homogenates were prepared from surgically removed nasal polyps in 38 patients and from tissue biopsies obtained during endoscopy in 18 patients. The tissues were homogenized with a mechanical homogenizer (B. Braun, Melsungen, Germany), centrifuged, and separated. Supernatants were assayed for specific IgE levels using enzyme immunoassay for the quantitative determination of allergen-specific IgE as performed in human serum.

Inclusion criteria
All patients included in the study had history and clinical examination suggestive of allergy, positive serum total IgE, positive serum-specifi c IgE, and positive tissue-specifi c IgE. Th e symptoms were evaluated using the SNOT-22 test for all patients. Total SNOT-22 for each patient and grand total SNOT-22 for all patients were calculated. On analysis of the 22 presenting symptoms of the SNOT-22 test, we found that the most common annoying presentation for all patients was 'nasal blockage and congestion' with the highest grand total score of 210, followed by 'embarrassment' with a grand total score of 184 and 'decreased sense of taste and smell' with a grand total score of 184. With respect to sneezing and postnasal discharge as allergyrelated symptoms, the grand total scores were 124 and 128, respectively.

Skin prick testing
All patients underwent an SPT. A total of 41 patients showed positive results of SPT (73.2%); six patients showed positive result to only one allergen (14.6%), four patients showed positive result to two allergens (9.8%), 12 patients showed positive result to three allergens (29.3%), and 19 patients showed positive result to more than three allergens (46.3%). However, 15 patients showed negative results to SPT (26.8%). Table 2 shows the results of SPT.

Total IgE
With respect to total IgE, all patients had a positive total IgE (>100 IU/ml). Th e total IgE ranged from 106 to 273 IU/ml with mean of 164.6 ± 38.

Discussion
In the common practice of respiratory allergy, the standard tool available is a careful history taking and physical examination followed by confi rmation of etiological diagnosis by high IgE level to specifi c inhalant allergen that is associated with the occurrence and duration of symptoms [9].  [11].
Furthermore, the majority of allergen-specifi c IgE in the blood of allergic patients does not originate from blood-derived B cells or plasma cells. Th is result of Eckl-Dorna et al. [12] suggests local IgE production in tissues as a major source for allergen-specifi c IgE.
In this study, we depended on positive history taking, clinical examination, total IgE, serum-specifi c IgE, and tissue-specifi c IgE for diagnosis of allergic rhinitis instead of NPT, and we checked SPT sensitivity.
Th e sensitivity of a test is defi ned as the proportion of the patients who were reported as positive by the test [3]. We found that 41 patients showed positive results to SPT (73.2%) and 15 patients showed negative results to SPT (26.8%). Demoly et al. [13] considered SPT as highly sensitive test, 80-97%, to diagnose inhalant allergies. Th e positive predictive value to diagnose allergic rhinitis based only on the clinical history was 77% for persistent allergy and 82-85% for intermittent seasonal allergy [14]. Th is increased to 97-99% when SPT was utilized [14].
Sensitivity of SPT is lower for food allergens, ranging from 30 to 90% depending on the type of allergen and methods utilized -that is, pricking with extracts versus prick-to-prick techniques described earlier [15]. Double-blind placebo-controlled challenge studies in children demonstrate that SPT possesses a positive predictive value of 76 and 89% for clinical reactions to cow's milk and hen's egg, respectively [16].
Th e clinical relevance of SPT results varies, depending on the allergen utilized and the population tested. For example, sensitization to house dust mite (HDM) occurs in some individuals in the absence of clinical relevance [17]. Furthermore, sensitization to aeroallergens, as measured by SPT, may precede symptomatic allergy. Prospective studies showed that 30-60% of such individuals become allergic depending on the type of allergen tested and the time to followup [1].
Sensitization rates vary depending on the geographic region as measured in population-based and in patientbased studies. Exposure rates and genetic diff erences can explain some of these variations [18]. With increased human mobility, diff erences in exposure to various fl ora or alterations in the allergenicity of pollen, possibly caused by pollution [19] and by changes in sensitization, occur over time [20]. Longitudinal studies investigating sensitization over time provide data on such trends [21].
Our study carried out over a period of 2.5 years [1] advised that studies on allergic sensitization should be conducted over an extended period of time, ideally a year, as (i) skin test reactivity increases during the pollen season [22] and (ii) allergic individuals tend to seek care when they have symptoms. Th is can skew detected prevalence of sensitization in such studies.
Patients with nasal polyposis who show positive result of SPT range from 24 to 75%. In a study conducted by Munoz Del Castillo et al. [23], which involved 190 patients with nasal polyposis and 190 normal individuals as a control group, they found that 63.2% of the patients with nasal polyposis had positive SPT for at least one allergen, and 36.8% had negative results, showing a signifi cant diff erence compared with the control group.
In the present study, the most common allergens with positive results in SPT were 'House dust' with positive results in 19/41 patients (46.3%) and 'Pollens' with positive results in 18/41 patients (43.9%).
Some studies revealed extensive sensitization (80% of patients with nasal polyposis) especially to HDM, which is a much higher percentage than that observed in our study, which was 17/41 patients (41.5%).
Although there is little information about the prevalence of fungal allergies among patients with chronic rhinosinusitis, it is estimated to be 52%. In 2009, a study conducted shows that 22.4% of patients with nasal polyposis with allergy signs and symptoms had positive IgE to some fungal allergens [24].
In our study, the prevalence of fungal allergies among the SPT-positive patients was 46.3% (19/41 A study conducted by Collins et al. [27] supported the opinion that nasal polyps may have a more common relationship with food allergies than typical IgEmediated inhalant allergies. Th ey found that 43% of their patients with nasal polyposis had positive SPT and 70% had positive intradermal food test to an average of four foodstuff s.
On the basis of questionnaires, food allergy was reported by 22% [28] and 31% [29] of patients with nasal polyposis, which was signifi cantly higher than in non-nasal polyposis controls.  [30], which detected the prevalence of food allergy among 150 patients attending Ain Shams allergy clinic with allergic rhinitis. Th ey estimated the prevalence of food allergy to be 26% in test population and found that the prevalence of sensitization to specifi c food allergens ranged from 2.6% for wheat to 33.3% for strawberry. Th ey concluded that the prevalence of probable IgE-mediated food reactions is indeed uncommon in adults with allergic rhinitis.
In this study, we found that 15 patients showed negative results to SPT (26.8%). Th is result is comparable with Rondon et al. [31] study. Th ey defi ned local allergic rhinitis (LAR) on the basis of negative SPT and serum-specifi c IgE and positive NPT. It was diagnosed in 25.7% patients in a survey conducted on 428 patients with rhinitis. Th e HDM was the main sensitizing aeroallergen both in LAR and allergic rhinitis (60 and 54%, respectively) in their study [31].
Th us, before delivering a diagnosis of nonallergic rhinitis or asthma in patients with negative SPT to common allergen, further tests are needed [9].
Diagnosis of allergy has obvious consequences on patient management, including allergen avoidance, patient's education, and specifi c immunotherapy. We have to consider allergic rhinitis with negative SPT and LAR in management of patients with nasal polyposis to not miss diagnosis of allergy.
Further studies will be required to further defi ne the immunopathology, prevalence, practical diagnostic tests, and management.