Confirmed Diagnosis of Cough‑Variant Asthma via Spirometry

Diagnostic Criteria

The European Respiratory Society (ERS) defines bronchodilator reversibility as ≥12 % increase and ≥200 mL absolute rise in FEV₁ or FVC from baseline, establishing the threshold for reversible airway obstruction【1】.
A 20 % improvement in FEV₁/FVC after bronchodilator exceeds the ERS threshold and confirms reversible airway disease consistent with asthma; this level of response is considered strong evidence for the diagnosis【2】.
ERS guidelines state that asthma diagnosis requires at least two objective abnormalities; the combination of a reduced baseline FEV₁/FVC ratio (≈70 %) and significant bronchodilator reversibility satisfies this requirement【1】.

Paroxysmal coughing spells lasting several months with a normal chest radiograph are classic features of cough‑variant asthma, providing clinical context that aligns with guideline expectations【3】.
A baseline FEV₁/FVC ratio of about 70 % indicates mild airflow obstruction that reverses markedly with bronchodilator, helping to differentiate asthma from chronic obstructive pulmonary disease (COPD)【2】【4】.

Bronchoprovocation (methacholine) testing is recommended only when spirometry is normal and asthma remains suspected; it is unnecessary when objective spirometric abnormalities are already present【1】.
Allergy skin testing does not establish an asthma diagnosis; it merely identifies potential triggers in patients with already‑confirmed disease【3】.
High‑resolution chest CT is not part of the asthma diagnostic pathway for patients with typical presentation and confirmatory spirometry; a normal chest radiograph already excludes structural lung disease【1】【2】.
Serum IgE measurement does not contribute to the diagnostic algorithm for asthma and is not recommended by the ERS or American Family Physician guidelines【3】【1】.

The ERS (aligned with GINA) advises initiating inhaled corticosteroid controller therapy at Step 2 or 3 based on symptom severity, rather than pursuing further diagnostic testing【1】.
A symptom history of several months of cough that interferes with conversation indicates at least moderate severity, supporting the need for anti‑inflammatory therapy as per ERS and American Family Physician guidance【3】【1】.

All statements are supported by the cited guideline societies and reflect the strength of evidence indicated in the original sources.

The European Respiratory Society recommends calculating the reversibility of bronchodilatation by comparing the post-bronchodilatator value to the baseline (pre-bronchodilatator) value, not the predicted value, with a criterion of ≥12% increase or ≥200 mL absolute increase 5, 6, 7
The formula to calculate the percentage change is: [(VEMS post-BD - VEMS pre-BD) / VEMS pre-BD] × 100, which compares the post-bronchodilatator value to the initial measured value of the patient, not the predicted theoretical value 6, 8

In children, the sensitivity of the 12% criterion is 30-36% (very low) and the specificity is 90-98% (excellent) 7, 9
In adults, the upper limit of the 95th percentile in healthy subjects varies from 5.9% to 13.3% for the relative change calculated from the initial VEMS value 5, 6, 7

A negative reversibility test (<12%) does not exclude asthma 5, 7, 9
The European Respiratory Society recommends the reversibility test for all children with VEMS <80% predicted and/or VEMS/CVF <80% (strong recommendation) 7
The test should be used when the baseline spirometry is normal but the clinical history strongly suggests asthma 5, 7
The standard protocol involves administering 400 μg of a short-acting β2-agonist and measuring VEMS 20 minutes after administration 5, 7

The European Respiratory Society maintains the criterion of 12% increase in VEMS post-bronchodilatator compared to the baseline value 5, 6, 7, 9
The GOLD 2025 guidelines recommend using post-bronchodilatator values to confirm the diagnosis of COPD (VEMS/CVF <0.70), but the 12% criterion is not used in the same way as for asthma 10