Good link for normal values here.
- FEV1/FVC ratio is 70% or higher in restrictive disease and <70% in obstructive.
- Restrictive disease will show reduction in both FEV1 and FVC, proportionately (FEV1 <80% but FEV1/FVC ratio 70% or higher)
- Reversibility testing can be done with 2.5 mg Salbutamol, 2 weeks of 30 mg oral pred, or six minutes of exercise. Positive reversibility is >15% FEV1.
- Spirometry can underestimate the FVC in patients with severe COPD as it takes them longer than 15 seconds to empty their lungs.
NICE guidance on COPD classification:
- Mild (Stage 1) – FEV1 80% or greater
- Moderate (Stage 2) – FEV1 50 – <80% predicted
- Severe (Stage 3) – 30 – FEV1 <50% predicted
- Very severe (Stage 4) – FEV1 <30% predicted, or FEV1 <50% predicted with associated respiratory failure
all of which should also have FEV1/FVC <70%