Appropriate Antigen Concentrations and Timing of a Nasal Provocation Test

Purpose: We aimed to determine appropriate antigen concentrations and the right time to evaluate intranasal changes when performing a nasal provocation test (NPT). Also, we sought to analyze the diagnostic usefulness of individual nasal symptom and peak nasal inspiratory flow (PNIF).

Materials and methods: We divided 46 patients into allergic rhinitis (AR) group (n=19) and a non-allergic rhinitis (NAR) group (n=27). We performed intranasal challenge with 100 AU/mL of Dermatophagoides pteronyssinus (DP) and measured changes in nasal symptoms [scored using the visual analogue scale (VAS)] and PNIF%. If the patient showed significant changes, VAS and PNIF were assessed again after another 15 minutes. In patients without significant changes, we administered 1000 AU/mL and measured changes in nasal symptoms and PNIF% after 15 and 30 minutes.

Results: Fifteen minutes after the 100 AU/mL challenge, the AR group showed more significant VAS changes in all nasal symptoms, total nasal symptom score (TNSS), and PNIF% change than the NAR group. Among the AR group, patients who did not respond to 100 AU/mL exhibited less significant differences relative to the NAR group, even after 1000 AU/mL challenge.

Receiver operating characteristic curve analysis for VAS changes 15 minutes after 100 AU/mL challenge revealed that all nasal symptoms had area under the curve (AUC) values of ≥0.84 (p<0.001). TNSS change had an AUC value of 0.929 (p<0.001), while PNIF% change had an AUC value of 0.834.

Conclusion: We could determine the optimal concentration (100 AU/mL), timing (15 minutes after challenge), and parameters (changes in TNSS and PNIF%) when performing NPT.

Background Antigen-detecting rapid diagnostic tests (Ag-RDT) for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) offer new opportunities for the quick and laboratory-independent identification of infected individuals for control of the SARS-CoV-2 pandemic. Despite the potential benefits, nasopharyngeal sample collection is frequently perceived as uncomfortable by patients and requires trained healthcare personnel with protective equipment. Therefore, anterior nasal self-sampling is increasingly recognized as a valuable alternative.

Methods We performed a prospective, single-center, point of care validation of an Ag-RDT using a polypropylene absorbent collector for standardized self-collected anterior nasal swabs. Real-time polymerase chain reaction (RT-PCR) from combined oropharyngeal/nasopharyngeal swabs served as a comparator. Primary endpoint was sensitivity of the standardized Ag-RDT in symptomatic patients with medium or high viral concentration (≥1 million RNA copies on RT-PCR for SARS-CoV-2).

 Results Between 12 February and 22 March 2021, 388 participants were enrolled. After exclusion of 9 patients for which no PCR result could be obtained, the novel Ag-RDT was evaluated based on 379 participants, of whom 273 were symptomatic and 106 asymptomatic.

In 61 samples from symptomatic patients with medium or high viral load (≥1 million RNA copies), the sensitivity of the standardized Ag-RDT was 96.7% (59/61; 95% confidence interval (CI): 88.7-99.6%) for the primary endpoint. In total, 62 positive Ag-RDT results were detected out of 70 RT-PCR positive individuals, yielding an overall sensitivity of 88.6% (95% CI: 78.7-94.9%). Specificity was 99.7% (95% CI: 98.2-100%) in 309 RT-PCR negative individuals.

 Conclusions Here, we present a validation of a Roche Antigen Nasal Test Ag-RDT with a standardized sampling process for anterior nasal self-collection, which meets World Health Organisation (WHO) criteria of ≥80% sensitivity and ≥97% specificity. Although less sensitive than RT-PCR, this assay could be beneficial due to its rapid results, ease of use, and suitability for standardized self-testing.

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