Usefulness of mannitol challenge testing for diagnosing asthma in everyday clinical practice

Background: The mannitol test is widely used for assessment of airway responsiveness in patients with possible asthma, but our knowledge of the value in everyday clinical practice is limited. Objective: To investigate the diagnostic value of the mannitol test in a clinical setting. Methods: All patients having a mannitol challenge test as part of their diagnostic work-up for asthma at the respiratory outpatient clinic, Hvidovre Hospital, over a 5-year period were included in the present analysis. Case history, including previous diagnoses, spirometry, exhaled nitric oxide (F _E NO) was obtained. The mannitol challenge was performed according to guidelines, i.e. increasing doses of mannitol (from 5 to 635 mg) until maximum dose or a 15% decline in FEV ₁ (PD ₁₅ ) was achieved (positive test defined as a PD ₁₅ < 635 mg). Results: Our cohort comprised 566 patients (210 men). Post-challenge, 247 patients were diagnosed with asthma by a specialist in respiratory medicine, of whom 138 (56%) had a positive mannitol test. A diagnosis of asthma was ruled out by the specialist in 319 individuals, of whom 18 (6%) had a positive mannitol test and 77 (24%) previous doctor-diagnosed asthma (but with no evidence of a confirmatory test). The specificity and sensitivity of the test was 94% and 56%, respectively. Female gender (p = 0.005), increasing BMI (p < 0.001), exercise-induced cough (p = 0.002), night-time respiratory symptoms (p = 0.002), low FEV ₁ /FVC ratio (p = 0.008) and high F _E NO (p < 0.001) were determinants for a positive mannitol test. Conclusion: In everyday clinical work-up of patients with possible asthma, the sensitivity and specificity of the mannitol challenge test is comparable to previous controlled trials.