Asthma Management Handbook

Assessing lung function to investigate asthma-like symptoms in adults

Recommendations

Perform or arrange spirometry for every patient with suspected asthma.

Note: If reliable equipment and appropriately trained staff are available, spirometry can be performed in primary care. If not, refer to an appropriate provider such as an accredited respiratory function laboratory.

How this recommendation was developed

Consensus

Based on clinical experience and expert opinion (informed by evidence, where available).

Measure bronchodilator reversibility by performing spirometry before and after administration of a rapid-onset beta2 agonist bronchodilator (e.g. 4 puffs of salbutamol 100 mcg/actuation via pressurised metered-dose inhaler and spacer).

Notes 

Airflow limitation is defined as reversible (i.e. bronchodilator response is clinically important) if FEV1 increases by ≥200 mL and ≥12%.

Failure to demonstrate reversible airflow limitation after bronchodilator (‘bronchodilator reversibility’) does not exclude asthma, and its presence does not prove asthma – the pattern of symptoms and other clinical features must also be considered. 

How this recommendation was developed

Consensus

Based on clinical experience and expert opinion (informed by evidence, where available).

Record the ratio of FEV1 to FVC (FEV1/FVC). Before making the diagnosis of asthma, confirm that FEV1/FVC is reduced (less than the lower limit of normal for age) at a time when FEV1 is lower than predicted.

Note: If the spirometer does not provide lower limit of normal for age, use the follow age-based cut-points to indicate expiratory airflow limitation in adults and older adolescents:

  • less than 0.85 (up to 19 years)
  • less than 0.80 (20–39 years)
  • less than 0.75 (40–59 years)
  • less than 0.70 (60 years and older).
How this recommendation was developed

Consensus

Based on clinical experience and expert opinion (informed by evidence, where available), with particular reference to the following source(s):

  • National Heart Lung and Blood Institute (NHLBI) National Asthma Education and Prevention Program, 20071
  • Johns and Pierce, 20112
  • Quanjer et al. 20123

If a patient shows some improvement in FEV1 after bronchodilator, but does not meet criteria for reversible airflow limitation, consider other investigations. If necessary, repeat spirometry after a treatment trial of 4–6 weeks with regular low-dose inhaled corticosteroid plus short-acting beta2 agonist as needed, to see if there is a significant improvement in symptoms and lung function.

Note: Airflow limitation can be transient (e.g. when recorded during a severe acute infection of the respiratory tract) and does not necessarily mean that the person has chronic asthma. Ideally, airflow limitation should be confirmed when the patient does not have a respiratory tract infection.

How this recommendation was developed

Consensus

Based on clinical experience and expert opinion (informed by evidence, where available).

Hand-held lung function-measuring devices (designed to measure FEV1 and/or FEV6, but not FVC) can be used in COPD case-finding and may also be useful in asthma case-finding, but must not be relied on either for ruling out asthma or when making a definitive diagnosis of asthma, because there is not enough evidence and validated protocols have not been developed.

How this recommendation was developed

Consensus

Based on clinical experience and expert opinion (informed by evidence, where available).

Do not use peak flow meters in place of spirometry for diagnosing asthma.

How this recommendation was developed

Consensus

Based on clinical experience and expert opinion (informed by evidence, where available).

More information

Spirometry in diagnosis and monitoring

Spirometry is the best lung function test for diagnosing asthma and for measuring lung function when assessing asthma control. Spirometry can:

  • detect airflow limitation
  • measure the degree of airflow limitation compared with predicted normal airflow (or with personal best)
  • demonstrate whether airflow limitation is reversible.

It should be performed by well-trained operators with well-maintained and calibrated equipment.4, 5

Before performing spirometry, check if the person has any contraindications (e.g. myocardial infarction, angina, aneurysm, recent surgery, suspected pulmonary embolism, suspected pneumothorax, fractured ribs). Advise them to stop if they become dizzy.

Clearly explain and physically demonstrate correct spirometry technique: 2

  • Sit upright with legs uncrossed and feet flat on the floor and do not lean forward.
  • Breathe in rapidly until lungs feel absolutely full. (Coaching is essential to do this properly.)
  • Do not pause for more than 1 second.
  • Place mouthpiece in mouth and close lips to form a tight seal.
  • Blast air out as hard and fast as possible and for as long as possible, until the lungs are completely empty or you are unable to blow out any longer.
  • Remove mouthpiece.

Repeat the test until you obtain three acceptable tests and these meet repeatability criteria.

Acceptability of test

A test is acceptable if all the following apply:

  • forced expiration started immediately after full inspiration
  • expiration started rapidly
  • maximal expiratory effort was maintained throughout the test, with no stops
  • the patient did not cough during the test
  • the patient did not stop early (before 6 seconds for adults and children over 10 years, or before 3 seconds for children under 10 years).

Record the highest FEV1 and FVC result from the three acceptable tests, even if they come from separate blows.2

Repeatability criteria

Repeatability criteria for a set of acceptable tests are met if both of the following apply:4

  • the difference between the highest and second-highest values for FEV1 is less than 150 mL
  • the difference between the highest and second-highest values for FVC is less than 150 mL.

For most people, it is not practical to make more than eight attempts to meet acceptability and repeatability criteria.2

Testing bronchodilator response (reversibility of airflow limitation)

Repeat spirometry 10-15 minutes after giving 4 separate puffs of salbutamol (100 mcg/actuation) via a pressurised metered-dose inhaler and spacer.2 (For patients who have reported unacceptable side-effects with 400 mcg, 2 puffs can be used.)

For adults and adolescents, record a clinically important bronchodilator response if FEV1 increases by ≥ 200 mL and ≥ 12%.2

For children, record a clinically important bronchodilator response if FEV1 increases by
≥ 12%.2

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Roles of other lung function tests in diagnosing asthma in adults

Peak expiratory flow meters in asthma diagnosis

Occasional measurement of peak expiratory flow rate using a peak flow meter is not as reliable as spirometry in the diagnosis of asthma and should not be used as a substitute.6

However, peak expiratory flow monitoring can be used to support the diagnosis of asthma in some patients (e.g. as one of several investigations in the assessment of suspected work-related asthma).

When using peak expiratory flow rate to measure lung function in diagnostic investigation, either of the following suggest a diagnosis of asthma:7

  • improvement in peak expiratory flow rate of at least 60 mL/min (or at least 20%) after inhaling a short-acting beta2 agonist bronchodilator, compared with baseline measure
  • diurnal variation in peak expiratory flow rate of more than 10% with twice-daily readings.

Hand-held lung function measuring devices

Small hand-held devices that measure FEV1 and/or FEV6 could be useful in primary care case-finding to detect patients who need full investigation for COPD.6 However, there is not enough evidence to recommend their use in asthma diagnosis at present.6

Other lung function tests used in further investigation

Tests of airway hyperresponsiveness, lung volume tests and diffusing capacity tests may have roles within further investigation of respiratory symptoms in some patients.

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Definition of variable expiratory airflow limitation

Most of the tests for variable expiratory airflow limitation are based on showing variability in FEV1. While reduced FEV1 may be seen with many other lung diseases (or due to poor spirometric technique), a reduced ratio of FEV1 to FVC indicates airflow limitation.8 Normal FEV1/FVC values derived from population studies vary,13 but are usually greater than:1

  • 0.85 in people aged up to 19 years
  • 0.80 in people aged 20–39 years
  • 0.75 in people aged 40–59 years
  • 0.70 in people aged 60–80 years.

In children, it is less useful to define expiratory airflow limitation according to a specific cut-off for FEV1/FVC ratio, because normal values in children change considerably with age.3

Some spirometers provide predicted normal values specific to age group. If these are available, a FEV1/FVC ratio less than the lower limit of normal (i.e. less than the 5th percentile of normal population) indicates airflow limitation.

Variable expiratory airflow limitation (beyond the range seen in healthy populations) can be documented if any of the following are recorded:

  • a clinically important increase in FEV1 (change in FEV1 of at least 200 mL and 12% from baseline for adults, or at least 12% from baseline for children) 10–15 minutes after administration of bronchodilator
  • clinically important variation in lung function (at least 20% change in FEV1) when measured repeatedly over time (e.g. spirometry on separate visits)
  • a clinically important reduction in lung function (decrease in FEV1 of at least 200 mL and 12% from baseline on spirometry, or decrease in peak expiratory flow rate by at least 20%) after exercise (formal laboratory-based exercise challenge testing uses different criteria for exercise-induced bronchoconstriction)
  • a clinically important increase in lung function (at least 200 mL and 12% from baseline) after a trial of 4 or more weeks of treatment with an inhaled corticosteroid
  • clinically important variation in peak expiratory flow (diurnal variability of more than 10%)
  • a clinically important reduction in lung function (15–20%, depending on the test) during a test for airway hyperresponsiveness (exercise challenge test or bronchial provocation test) measured by a respiratory function laboratory.

Notes

Patients referred to a respiratory function laboratory may be asked not to take certain medicines within a few hours to days before a spirometry visit.

A clinically important increase or decrease in lung function is defined as a change in FEV1 of at least 200 mL and 12% from baseline for adults, or at least 12% from baseline for children, or a change in peak expiratory flow rate of at least 20% on the same meter.58 A clinically important increase in FVC after administering bronchodilator may also indicate reversible airflow limitation, but FVC is a less reliable measure in primary care because FVC may vary due to factors such as variation in inspiratory volume or expiratory time.

The finding of ‘normal’ lung function during symptoms reduces the probability that a patient has asthma, but a clinically important improvement in response to bronchodilator or inhaled corticosteroid can occur in patients whose baseline value is within the predicted normal range.

The greater the variation in lung function, the more certain is the diagnosis of asthma. However, people with longstanding asthma may develop fixed airflow limitation.

Reversibility in airflow limitation may not be detected if the person is already taking a long-acting beta2 agonist or inhaled corticosteroid.

Airflow limitation can be transient and does not necessarily mean that the person has asthma (e.g. when recorded during a severe acute infection of the respiratory tract). Ideally, airflow limitation should be confirmed when the patient does not have a respiratory tract infection. Reduction in lung function during a respiratory tract infection with improvement in lung function after its resolution, commonly occurs in people with asthma, but can also be seen in patients with COPD or in healthy people without either asthma or COPD.9,10

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References

  1. National Heart Lung and Blood Institute (NHLBI) National Asthma Education and Prevention Program. Expert Panel Report 3: guidelines for the diagnosis and management of asthma. Full report 2007. US Department of Health and Human Services National Institutes of Health, Bethesda, 2007. Available from: http://www.nhlbi.nih.gov/health-pro/guidelines/current/asthma-guidelines/full-report
  2. Johns DP, Pierce R. Pocket guide to spirometry. 3rd edn. McGraw Hill, North Ryde, 2011.
  3. Quanjer PH, Stanojevic S, Cole TJ, et al. Multi-ethnic reference values for spirometry for the 3-95-yr age range: the global lung function 2012 equations. Eur Respir J. 2012; 40: 1324-43. Available from: http://www.ncbi.nlm.nih.gov/pubmed/22743675
  4. Miller MR, Hankinson J, Brusasco V, et al. Standardisation of spirometry. Eur Respir J. 2005; 26: 319-338. Available from: http://erj.ersjournals.com/content/26/2/319
  5. Levy ML, Quanjer PH, Booker R, et al. Diagnostic Spirometry in Primary Care: Proposed standards for general practice compliant with American Thoracic Society and European Respiratory Society recommendations. Prim Care Respir J. 2009; 18: 130-147. Available from: http://www.ncbi.nlm.nih.gov/pubmed/19684995
  6. National Asthma Council Australia. Asthma and lung function tests. An information paper for health professionals. National Asthma Council Australia, Melbourne, 2012. Available from: http://www.nationalasthma.org.au/publication/asthma-lung-function-tests-hp
  7. Global Initiative for Asthma (GINA). Global strategy for asthma management and prevention. GINA, 2012. Available from: http://www.ginasthma.org
  8. Pellegrino R, Viegi G, Brusasco V, et al. Interpretative strategies for lung function tests. Eur Respir J. 2005; 26: 948-968. Available from: http://erj.ersjournals.com/content/26/5/948
  9. Collier AM, Pimmel RL, Hasselblad V, et al. Spirometric changes in normal children with upper respiratory infections. Am Rev Respir Dis. 1978; 117: 47-53. Available from: http://www.ncbi.nlm.nih.gov/pubmed/619724
  10. Melbye H, Kongerud J, Vorland L. Reversible airflow limitation in adults with respiratory infection. Eur Respir J. 1994; 7: 1239-1245. Available from: http://www.ncbi.nlm.nih.gov/pubmed/7925901