The following criteria need to be satisfied:
• At least three technically satisfactory readings.
• The volume-time traces are smooth and free from irregularities suggesting a slow start, submaximal effort or coughing.
• At least two of the readings of FEV1 should be within 100mL or 5% of each other.
• The reading has been continued for long enough for a volume plateau to be achieved. This can take up to 15 s in patients with severe COPD.
• The best FEV1 and FVC are reported and compared with predicted normal results.
• Temperature and atmospheric pressure measurement may be appropriate in hospital lung function laboratories, but not in primary care.
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