Utility of routine radioallergosorbent test (RAST) testing at initial diagnosis of allergic rhinitis: a retrospective cohort study

Introduction

Allergic rhinitis (AR) is a common condition that affects 20% of the adult population and up to 10% of children in Australia (1). The condition is defined as an immunoglobulin E (IgE) and eosinophil-mediated inflammatory response of nasal mucous membranes to inhaled allergens in a sensitised individual (2-4). A clinical diagnosis can be made when patients present with a history consistent with an allergic cause and have one or more of the following symptoms of nasal congestion, nasal discharge, nasal or ocular pruritus, or sneezing (2,4). Supportive examination findings include clear rhinorrhoea, bluish or pale oedematous nasal mucosa, and scleral injection with epiphora (4).

Following clinical diagnosis of AR, it is reasonable, and common in practice, to institute empirical medical treatment (3-5). This may be in the form of intranasal corticosteroid or antihistamine sprays, or non-sedating oral antihistamines (2,4). Many patients will be well controlled with these treatments and will not require further investigation to formalise a definitive diagnosis (4-6). This approach to management following a clinical diagnosis is supported by the Clinical Practice Guidelines on Allergic Rhinitis by the American Academy of Otolaryngology-Head and Neck Surgery (6). These guidelines recommend investigations in the form of specific in-vivo or in-vitro allergy testing in patients with a clinical diagnosis of AR in the following circumstances: (I) failure to respond to empiric treatment; (II) when the diagnosis is uncertain; or (III) when knowledge of the specific causative allergen is needed to target therapy (6).

Serum specific IgE allergy testing in the form of a radioallergosorbent test (RAST) for aeroallergens is routinely performed at the initial consultation for patients presenting to public hospital-based otolaryngology outpatient clinics when they are first diagnosed with AR and commenced on empirical treatment. The clinical utility of this approach to patient management is uncertain. The potential benefits to this approach of routine RAST testing includes the ability to improve diagnostic certainty early in patient management allowing for adjustments to be made to treatment at their subsequent follow-up appointment (3,5,7). These adjustments to treatment may include advice on allergen avoidance, the avoidance of specific or potential environmental nonallergenic irritants, refining medication regimens, referral for allergen specific immunotherapy, or recommendation for surgical intervention for nasal obstruction (2,3). Additionally, by improving diagnostic certainty, excluding variants of non-AR, and making timely adjustments to management, treatment compliance may be enhanced, enabling tighter symptom control and improved patient quality of life. However, it is unclear whether these outcomes occur in the real world.

Given the uncertainty around the utility of routine RAST testing to patient management a review of this approach to practice is required. The purpose of this study is to investigate if there is a benefit to patient care from routine RAST testing at the initial diagnosis of AR when patients are first commenced on empirical treatment. It is expected that assessment of this approach to practice has the potential to improve the quality of patient care by ensuring that RAST testing is being recommended and utilised in a targeted manner. To our knowledge, this is the first study to address this topic.

Methods

A retrospective cohort study was conducted through the Department of Otolaryngology, Head and Neck Surgery at the Sunshine Coast University Hospital, a major teaching hospital in Queensland. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments, and approved by the Metro North Health Human Research Ethics Committee (project ID: 100427; HREC/2023/MNHA/100427). Patient confidentiality was maintained by anonymizing data, and individual consent was waived for this retrospective analysis. The study is reported according to the STROBE reporting guidelines (available at https://www.theajo.com/article/view/10.21037/ajo-25-24/rc).

Patient inclusion

Patients were initially identified for inclusion into the study by sourcing all RAST test results ordered through the Otolaryngology Outpatient Clinic from March 2019 to April 2023. A review of electronic medical records was performed and patients included in the study if they had been commenced on empirical treatment and were investigated with a RAST test at the same time as receiving an initial clinical diagnosis of AR.

Data collected included patient demographics, documented clinical history and examination findings used to formulate a clinical diagnosis of AR, RAST test results, and treatments recommended at initial consultation and follow-up. The following exclusion criteria were applied prior to final data analysis: age less than 2 years, pregnant patients, smokers and those exposed daily to other environmental irritants, patients who had interim treatment interventions for acute AR elsewhere, those on immunotherapy, those who also had a skin prick test (SPT), patients that failed to undergo RAST testing or were lost to follow-up, incomplete or uninterpretable medical records, and patients with documented treatment interventions for acute sinusitis in the 6 weeks prior to their first visit, or a viral rhinitis in the 3 weeks before their first visit. These were implemented to account for patients with symptoms attributable to non-allergic factors or concurrent acute illness of other causes.

Study design

Determining the utility of RAST testing was achieved by defining and comparing two principal outcome groups: Group A, representing the proportion of patients that received a benefit from RAST testing; and Group B, representing those that derived no benefit. The clinical benefit defined in this study refers to the initiation of targeted therapy to improve symptom control in patients poorly responsive to empirical therapy.

In Group A, there were two outcomes that constituted a benefit to patient treatment:

• Positive RAST test results that confirmed the diagnosis of AR and allowed for specific allergen avoidance, change in medical therapy, referral for targeted immunotherapy and/or recommendation for surgical intervention, in a patient whose symptoms were unchanged or poorly controlled by empirical treatment.
• Negative RAST test results in a patient whose symptoms were unchanged or poorly controlled on empirical treatment where the original diagnosis of AR was reassessed with a new diagnosis made with appropriate treatment instituted.

Treatment decisions were instituted in concordance with the Clinical Practice Guidelines on Allergic Rhinitis by the American Academy of Otolaryngology-Head and Neck Surgery based on individual patient indications (6). Subsequent management for RAST negative patients was specific to their new diagnosis and included new medication regimes and surgery.

In Group B, no benefit by testing was defined as patients presenting at follow-up with improved symptoms and therefore having no change made to treatment regardless of RAST test results.

Statistical analysis

The RAST test at Sunshine Coast University Hospital consists of a multiplex test that incorporates house dust mite, grass mix, and cat and dog dander with a binary result of being either positive or negative for each aeroallergen. To facilitate the comparison of two different benefit groups based on their RAST results, Chi-square test was used. This was used to test whether there was a difference among the two benefit groups, with respect to their RAST result. To conduct the analysis, R programming language software, version 4.4.0 was used. The null and alternate hypothesis for Chi-square test was given by: H0 (there is no difference among the proportions of the two benefit groups) and H1 (there is a difference among the proportions of the two benefit groups). Univariate analysis presented as odds ratios (ORs) and 95% confidence intervals (CIs) were used when comparing variables. A P value less than 0.05 was considered statistically significant. Subgroup analysis was performed within Group A to evaluate further treatment outcomes recommended at follow-up. Power analysis determined a sample size of 170 patients would be required to provide a power of 90% to reach a minimum sensitivity of 95% and type-I error probability (alpha) of 0.05.

Results

A total of 351 patients were identified at initial review, of which 247 met criteria for inclusion in the study. Demographic analysis showed an even sex distribution with 50.2% (n=124) being female and a predominantly younger cohort of patients, with 59.5% (n=147) aged less than 20 years [median 15 years, interquartile range (IQR), 36 years, range, 3–71 years of age]. Empirical treatment instituted at the initial consultation consisted of inhaled nasal corticosteroids in 53% (n=132), combination steroid/antihistamine nasal sprays in 46% (n=113), and oral antihistamines in 1% (n=2) of patients. Overall, there was a benefit to testing with 54% (n=134) of patients assigned to Group A. The total numbers for Group A and Group B are provided in Table 1, which subdivides these two groups based on their RAST results and shows that among both groups, the frequency of positive and negative RAST results were similar. For Group A the age distribution ranged from 3 to 70 years of age (median 12 years, IQR, 27 years) with 52% (n=68) being female and for Group B the age range was from 3 to 71 years of age (median 14 years, IQR, 36 years) with 47% (n=55) being female.

Comparison of these results (Table 1) measured by Chi square test showed that between Group A and Group B there was no statistically significant difference among the groups based on different RAST outcomes (OR =1.25; 95% CI: 0.76–2.05; P=0.4). To further evaluate the real-world applicability of the results in Group A, subgroup analysis was performed to identify treatment outcomes amongst this cohort of patients as further disease management. This was defined as the proportion of outcome prevalence for patients in Group A and is shown in Table 2. In Group A, 16% (n=21) of patients had two or more treatment outcomes recommended for the management of their AR.

To assess the relevance of RAST test results in Group A to the type of outcome measure implemented, each outcome measure was further analysed to evaluate the proportion of patients within each group to their corresponding RAST results (Table 3). For the outcomes of allergen avoidance, change in medical therapy, and immunotherapy, the RAST results were mainly positive. The two other measures of interest showed that for a new diagnosis made that most patients had a negative RAST result and that they were mainly positive in those referred to surgery. It was noted that in most cases, the new diagnosis for patients was that of non-AR or chronic rhinosinusitis (CRS). The most common surgical treatment recommended was to address nasal obstruction and consisted of cautery of inferior turbinates in children, and reduction of inferior turbinates for adolescent and adult patients.

Discussion

RAST testing is a valuable tool in the diagnostic workup of AR (4,6). While SPT is the gold standard due to its higher sensitivity and has the advantage of immediate results, RAST testing provides a practical alternative when SPT results are inconclusive or skin testing is not feasible, such as in patients with extensive inflammatory skin conditions, those taking antihistamines, or very young children (3,6). By identifying specific allergens, RAST testing can aid in guiding appropriate management and treatment strategies (3). Despite this, there is a requirement for judicious application of laboratory investigations to befit current models of best practice. This requirement formed the objective of our study to assess the clinical utility of a common practice towards patient investigation that is at odds with current otolaryngology clinical practice guidelines on management of AR (6).

Our results showed there was no statistical significance to the cohort benefiting from RAST testing in Group A compared to the non-benefit cohort of Group B (OR =1.25; 95% CI: 0.76–2.05; P=0.4). While these results do not show statistical significance, RAST testing had practical implications for clinical management of the patient cohort in this study. Whilst accepting that an accurate clinical assessment, including a typical history and clinical observations, are more likely to deliver a positive test, all patients in group A that had a positive RAST were able to have further dedicated management strategies implemented at their second outpatient visit that extended beyond the use of empirical medication administration. These included advice on allergen avoidance, a change to their medication regimen, referral for immunotherapy or surgery, or a combination of these outcomes. Interestingly, four of these patients received a new diagnosis (Table 3), which on review of the data corresponded to dual diagnosis of concomitant CRS with AR. With regards to Group B, most of these patients were RAST positive (Table 1). Although there was no immediate change to their management, and therefore no perceived benefit at subsequent outpatient review, it could be argued that having a positive result may be of use in future consultations by directing management options in the setting of failing symptom control with current empirical treatment. This could be of benefit in either the hospital or primary care setting following patient discharge.

The other two subgroups are those of RAST negative patients, which were the minority in both Group A and Group B (Table 1). When interpreting the results for these groups, the following comments can be made. For Group A patients, the main outcome was consideration of a new diagnosis, which occurred in 71% (n=30) of patients in this group (Table 3). The benefit of this outcome through allergy testing is based on changed diagnostic parameters with enhanced diagnostic certainty, which allows for formulation of a new diagnosis and institution of an appropriate treatment plan (3,8). The remaining patients were either referred for surgical intervention, had a medication regimen change, or were recommended for immunotherapy. Reasons for medication change and immunotherapy referral in this group were unclear on review of their medical records. Those patients in Group B represented 17% (n=41) of the total patients included in the study, and it is reasonable to suggest that these patients did not benefit in any meaningful way from RAST testing.

As a diagnostic test, RAST is convenient to clinician and patient alike, and can assist in determining patient sensitivity to common aeroallergens (7,9). Results can then be interpreted in the patient’s clinical context at their subsequent follow-up visit with the potential to streamline diagnostic certainty and treatment recommendations (3,7,9). In our study, more patients received a benefit from RAST testing than those who did not. The utility of this approach to formalising a diagnosis for these patients in Group A mainly concerns the ability to make management recommendations early on in their episode of care as demonstrated in the outcome measures implemented for this group at their subsequent review (Table 2). Had these patients not had allergy testing at their first outpatient visit, then the ability to change the approach to management would have been delayed, requiring implementation at a subsequent review. To emphasise this point, Sunshine Coast University Hospital quoted the cost of a RAST test to be $80, whereas an average otolaryngology outpatient clinic appointment costed the health service $586.

Otolaryngologists play an important role in the multidisciplinary management of AR, and to ensure best practice, must be clear on the indications for when to perform allergy testing (10). Medical history and examination findings can indeed be complemented by use of allergy testing to improve diagnostic certainty in those with a high pretest probability of allergy (4,7). A study by Crobach et al. (11), assessed the diagnostic power for medical history alone compared to medical history combined with RAST in making a diagnosis of AR in patients aged 12 years or over. They found that the diagnostic power on their logistic regression model for medical history alone ranged from 0.77 to 0.89 based on expert consensus (11). When RAST was added, this improved diagnostic power from 0.93 to 1.00 (11). The range in both investigation arms was dependent on the type of allergen responsible for AR (11). Conversely, in those with a low pre-test probability of allergy, RAST testing may assist with ruling out disease, an advantage as already discussed, for patients in our study from Group A with negative RAST results (5). The utility of confirming or reassessing a diagnosis by way of allergy testing at the initial diagnosis of AR is promoted by several peak bodies in various position papers and guidelines (3,7,12).

In the recently published International Consensus Statement on Allergy and Rhinology: Allergic Rhinitis (3) the use of RAST testing is recommended at point of care for confirming the diagnosis of AR and allowing directed treatment. Similar recommendations are made in the World Allergy Organization position paper (7) and the British Society of Allergy and Clinical Immunology guideline for the diagnosis and management of allergic and non-allergic rhinitis (12). Importantly, each of these position papers assert that the main utility of allergy testing at the time of diagnosis of AR, beyond diagnostic certainty, is in providing further treatment options to patients already on empirical treatment to optimise symptom control (3,7,12). These treatment options have been discussed and include allergen avoidance, medication change, immunotherapy and/or surgery for nasal obstruction (3,7,12). Given that symptom control is the major factor in assessing a successful treatment response for patients with AR (13) it seems clinically prudent for otolaryngologists to consider adopting this strategy of early allergy testing to ensure optimal individualised patient management and long-term compliance in treatment.

We acknowledge that this study is not without its limitations. A single centre retrospective study such as this may not represent patient cohorts with dissimilar demographics as seen in other outpatient settings. Subsets of patients within a single centre may be different in terms of their micro- or macro-environments, but also their main symptom complaint as compared to those referred to respiratory or allergy outpatient clinics. This makes comparison of our study within regions and between specialties problematic and may affect the generalisability of our findings. The routine multiplex RAST test available at our centre assessed four common aeroallergens, meaning that other common aeroallergens, such as mould, were not tested. This may limit the generalisability of our results to other centres with different RAST allergen panels. It is important to note that the benefit of testing could be enhanced by expanding the panel of allergens used in RAST testing or by adding total IgE testing, where a raised level with negative individual allergen specific RAST tests could indicate one or more unidentified allergens This may represent an opportunity for future prospective comparative studies. Moreover, further research on how this compares with the gold standard of skin prick testing (being the practice of the senior author) could also be conducted. This study also lacked statistical significance between the two major benefit groups. This is potentially overcome by discussion of the clinical significance of the outcomes observed as they relate to individualised patient management and the consideration given of how routine RAST testing aligns with current peak body guidelines in the fields of both otolaryngology and allergy.

Conclusions

The current paradigms for management of AR in the Australian community are informed by individual clinician and institution specific practices. This is evident in our study where RAST testing is in widespread use at the initial diagnosis of AR, a practice that counters the otolaryngology specific guidelines that exist on management of this disease process. Of course, as with all guidelines, they need to be interpreted in the clinical setting and applied to the individual patient. In the setting of a busy public Otolaryngology Outpatient Department, RAST testing is a reasonable option to investigate for causative allergens at the outset of the diagnostic workup for AR. This approach may streamline patient management by enabling earlier implementation of tailored treatment strategies at subsequent review. We hope other units benefit from this study by allowing further research on this topic and the development of local guidelines for Otolaryngology Departments that manage this common condition.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://www.theajo.com/article/view/10.21037/ajo-25-24/rc

Data Sharing Statement: Available at https://www.theajo.com/article/view/10.21037/ajo-25-24/dss

Peer Review File: Available at https://www.theajo.com/article/view/10.21037/ajo-25-24/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://www.theajo.com/article/view/10.21037/ajo-25-24/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments, and approved by the Metro North Health Human Research Ethics Committee (project ID: 100427; HREC/2023/MNHA/100427). Patient confidentiality was maintained by anonymizing data, and individual consent was waived for this retrospective analysis.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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