Nasal smear eosinophilia for the diagnosis of allergic rhinitis and eosinophilic non-allergic rhinitis

Abstract

Objective - To evaluate nasal smear eosinophilia for the diagnosis of allergic rhinitis and eosinophilic non-allergic rhinitis in general practice. Design - Nasal smear eosinophilia was assessed and compared with 'consensus diagnoses' made by three experts in a modified Delphi method. Setting - Nineteen general practices in The Netherlands. Subjects - 363 consecutive patients aged 12 years or over who visited their general practitioner because of chronic or recurrent nasal symptoms between 1 March 1990 and 1 March 1991. Main outcome measures - The predictive value of nasal smear eosinophilia for allergic rhinitis; the prevalence of eosinophilic non-allergic rhinitis. Results - The positive predictive value of nasal smear eosinophilia (≥10% eosinophils) for allergic rhinitis was 30/37 = 81% (95% confidence interval (CI): 65-92%), the negative predictive value 172/312 = 55% (95% CI: 50-61%). Addition of the result of nasal smear eosinophilia to the information that was already obtained from the medical history resulted in a significant but very small improvement in the discrimination between patients with and without allergic rhinitis. The prevalence of eosinophilic non-allergic rhinitis was 7/349 = 2.0% (95% CI: 0.8-4.1%). Conclusion - Nasal smear eosinophilia contributes significantly to the diagnosis of allergic rhinitis; however, this contribution is very small and considered clinically irrelevant. Eosinophilic non-allergic rhinitis has a low prevalence; identifying this disorder is of minor importance. In conclusion, nasal smear eosinophilia is not recommended for use in general practice.