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Educational draft · awaiting clinical reviewUse Rapid for revision, not patient-care decisions. Check current national and local guidance and the BNF or BNFC before acting.

Spirometry, bronchodilator reversibility and peak flow

Respiratory · UK scope · Sources checked 27 Aug 2026 · Clinical review pending

RapidFull

Synopsis

Obtain and interpret quality-assured airflow measurements, distinguish obstruction from possible restriction, and use variability or reversibility as evidence without confusing a test result with a diagnosis.

  • Check identity, age, sex, height, indication, contraindications, current symptoms and recent bronchodilator use before testing.
  • FEV1 is the volume expired in the first second; FVC is the total forced expiratory volume; the FEV1/FVC ratio identifies airflow obstruction.
  • Interpret against appropriate reference values and the lower limit of normal where available; a fixed ratio below 0.70 supports COPD only in the right clinical context and can overdiagnose older adults.
  • A low FEV1/FVC indicates obstruction. A preserved/high ratio with low FVC suggests possible restriction or suboptimal effort and requires lung-volume confirmation, not a spirometric diagnosis of restriction.
  • For adult asthma, NICE supports bronchodilator reversibility when FEV1 rises by at least 12% and 200 mL from baseline, or at least 10% of predicted FEV1.
  • The NG245 evidence protocol uses 400 micrograms salbutamol through a spacer, with repeat spirometry after an appropriate interval; record drug, dose and time.
  • If spirometry is unavailable or delayed in suspected adult asthma, twice-daily PEF for 2 weeks supports asthma when mean diurnal variability is 20% or more.
  • A negative reversibility or variability test does not exclude asthma, especially when asymptomatic or already taking inhaled corticosteroid.
  • Peak flow is effort- and device-dependent; use the same meter, technique and personal best for monitoring, not a single isolated reading.
  • Never perform routine diagnostic spirometry during an acute attack when it would delay treatment or be unsafe.

Key red flags

Unsafe or invalid test setting

Acute cardiorespiratory instability, active significant haemoptysis, recent relevant thoracic/abdominal/eye surgery, untreated pneumothorax, severe infection-control risk or inability to follow instructions requires deferral or specialist assessment.

Investigation priorities

01
Pre-test clinical and medicine checkFirst step

Decide whether testing is safe and whether bronchodilator washout is appropriate.

Management branches

PatternFrom numbers to a physiological statement

Any acceptable spirometry result.

  1. 1. Confirm acceptability, repeatability, reference equation and whether result is pre- or post-bronchodilator.
  2. 2. Read FEV1/FVC first: below LLN indicates obstruction; then use FEV1 to describe impairment without equating it to symptom burden.
  3. 3. If the ratio is preserved but FVC is low, state 'possible restriction or incomplete exhalation' and arrange lung volumes where clinically indicated.
  4. 4. Inspect the curves for poor start, cough, truncation, scooping or fixed/variable upper-airway patterns; integrate symptoms and imaging before naming disease.

Key medicines

Salbutamol for bronchodilator reversibility testing400 micrograms inhaled through a spacer (typically 4 actuations of a 100 microgram metered-dose inhaler), then repeat spirometry after the protocol interval, commonly about 15 minutes.Document pre-test bronchodilator use. May cause tremor, tachycardia or hypokalaemia; defer or seek senior advice in unstable patients. A negative response does not exclude asthma and a positive response is not uniquely diagnostic.
Ipratropium as an alternative reversibility agent in specialist protocolsA common protocol uses 160 micrograms inhaled (for example 8 actuations of a 20 microgram inhaler) with repeat testing after about 30 minutes; follow the physiology laboratory protocol and product licence.Not the NG245 default asthma diagnostic protocol. Avoid spray into eyes; use caution with narrow-angle glaucoma and bladder-outflow problems. Record exact device, dose and interval.
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Sources and review status4 sources · checked 27 Aug 2026 · clinical review pending+
Sources

Sources and review status

National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.

  • NICE NG245: asthma diagnosis, monitoring and chronic managementAdult diagnostic sequence, reversibility and PEF thresholds.
  • NICE NG245 evidence review B: bronchodilator reversibility400 microgram salbutamol test protocol and diagnostic accuracy.
  • NICE NG115: COPD diagnosis and managementPost-bronchodilator spirometry and COPD interpretation.
  • NHS England adult breathlessness diagnostic pathwaySystematic assessment and spirometry placement in undifferentiated breathlessness.

Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes

Authoring stateRapid draftClinical stateAwaiting reviewJurisdictionUnited Kingdom