The bronchodilator test
When spirometry shows obstruction, we ask whether the airways can be opened up. The patient does spirometry, then inhales a fast-acting reliever — usually a short-acting beta-agonist like salbutamol through a spacer — waits about 10–15 minutes, and repeats the test. The change is the test for bronchodilator reversibility.
A meaningful response — traditionally an FEV1 (or FVC) rise of at least about 12% and 200 mL — shows the obstruction is at least partly reversible, which leans toward asthma. Obstruction that barely budges leans more toward fixed disease such as COPD. But the line is not absolute: many people with COPD show some reversibility, and asthma can look fixed during a bad spell, so the test informs the diagnosis rather than settling it alone.
Pre-bronchodilator FEV1 = 1.80 L Post-bronchodilator FEV1 = 2.10 L Absolute change = 2.10 - 1.80 = 0.30 L = 300 mL Percent change = 300 / 1800 = 16.7% Both thresholds met (>=200 mL AND >=12%) -> significant reversibility -> supports asthma
Peak flow at home
Peak expiratory flow is the single fastest speed of a forced blow, measured with a cheap handheld meter. It is far less detailed than full spirometry, but its power is that it can be done every day at home. Peak flow monitoring over weeks reveals patterns a one-off clinic test cannot — especially in asthma, where the airways change from hour to hour.
- Stand or sit upright and slide the marker to zero.
- Take the deepest breath you can, seal your lips around the mouthpiece.
- Blow out as hard and fast as you can in one sharp puff; record the number.
- Repeat three times and keep the highest; log morning and evening to watch the trend.