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Step 2. Confirm diagnosis of asthma using spirometry or peak expiratory flow rate (PEFR). Histamine or methacholine challenge test if necessary.

Confirmation of asthma requires the demonstration of reversible airways obstruction.
Airway reversibility defined as:
- FEV₁ > 12-15% inhaled post-bronchodilator;
- FEV₁ > 20% post steroid trial;
- PC₂₀ Ł 8mg/ml or equivalent (non-specific bronchial hyperreactivity using histamine or methacholine).

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Postgraduate Diploma in Occupational Health (DOH) - Modules 3 – 5: Occupational Medicine & Toxicology by Prof Rodney Ehrlich & Prof Mohamed Jeebhay is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.
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