Approach

The diagnosis of asthma has been the subject of debate among the major UK guideline authorities. Recommendations in this topic are based primarily on the British Thoracic Society/Scottish Intercollegiate Guidelines Network (BTS/SIGN) guideline, which was last updated in July 2019, but key differences from the National Institute for Health and Care Excellence (NICE) guideline are also outlined. Follow the recommended approach in your region.

The diagnosis of asthma is a clinical one.[1] Diagnose asthma based on the presence of typical symptoms along with objective tests demonstrating evidence of variable airflow obstruction and/or airway inflammation.[55][56]

For information specific to diagnosing exacerbations, see Acute asthma exacerbation in adults.

Practical approach to asthma diagnosis in adults

BTS/SIGN recommend categorising the patient according to their likelihood of having asthma based on an initial structured clinical assessment aimed at identifying typical signs and symptoms and checking medical history.[55] Subsequent investigations and treatment trials are based on this initial probability assessment.

The flowchart below represents the step-by-step approach recommended by BTS/SIGN. Further details on each step are provided in subsequent sections.

[Figure caption and citation for the preceding image starts]: ​Diagnostic flowchart; reproduced from BTS/SIGN “British guideline on the management of asthma”British Thoracic Society; Scottish Intercollegiate Guidelines Network. British guideline on the management of asthma​. First published 2003. Revised edition published July 2019; used with permission [Citation ends].com.bmj.content.model.Caption@2a29b570

For comparison, the diagnostic path recommended by NICE is summarised in the flowchart below.[Figure caption and citation for the preceding image starts]: ​Objective tests for asthma in adults aged 17 and over; reproduced from NICE “Asthma: diagnosis, monitoring and chronic asthma management”National Institute for Health and Care Excellence. Algorithm C: Objective tests for asthma in adults aged 17 and over. 2017 [internet publication]; used with permission [Citation ends].com.bmj.content.model.Caption@3c788694

The differences from BTS/SIGN are covered in more depth in the relevant sections that follow.

Global Initiative for Asthma (GINA) guidance advises that peak expiratory flow (PEF) measurement can be used as an alternative to spirometry where spirometry services are not available. Although PEF is less reliable than spirometry, its use is preferred where diagnosis would otherwise rely on symptoms only.[1]

Structured clinical assessment (BTS/SIGN)

If a patient presents with symptoms suggestive of asthma, carry out a structured clinical assessment to establish whether their likelihood of having asthma is of high, intermediate, or low probability.[55] Base the structured clinical assessment on a combination of the history, examination, and the patient's records.[55]

  • Note the disparity between BTS/SIGN and NICE recommendations; NICE also recommends a structured clinical assessment but does not refer to probabilities of asthma in its guideline. According to NICE, any individual suspected of having asthma should receive a series of objective tests before a diagnosis is made.[56]

BTS/SIGN recommend basing the initial probability of asthma on the following typical clinical features:[55]

  • A history of recurrent episodes (attacks) of symptoms, ideally corroborated by differences in PEF between symptomatic and asymptomatic periods

  • Any two or more of the following symptoms that vary over time: wheeze; cough; breathlessness; chest tightness

  • Recorded observation of wheeze heard by a healthcare professional

  • Personal/family history of other atopic conditions (in particular, atopic eczema/dermatitis, allergic rhinitis) or family history of asthma

  • No symptoms/signs to suggest an alternative diagnosis.

If the patient has all of these typical clinical features, consider them to have a high probability of asthma.[55]

  • Given the high probability of the patient having asthma, a trial of treatment is a pragmatic next step, particularly in symptomatic patients. See Management for more details.

  • An asthma diagnosis can be confirmed if the patient has a good response to treatment (both improvement in symptoms and objective improvements in lung function).

If the patient has some, but not all, of the typical features of asthma, or they have a poor response to an initial trial of treatment, assess them as having an intermediate probability of asthma.[55]

  • Further investigation is needed before a diagnosis can be made, and, unless the patient is acutely unwell, before treatment is started (or continued, if the patient had a poor response to an initial trial of treatment).

  • Use spirometry, with bronchodilator reversibility (BDR) testing, as the next step to investigate an intermediate probability of asthma.[55] See Investigations.

If the patient has none of the typical features of asthma, or presents with features more suggestive of an alternative diagnosis, the probability of asthma is low.[55]

  • Bear in mind that there will be a minority of patients who will have asthma even though the presentation is atypical.

  • Manage low-probability patients according to the most likely differential diagnosis. See Differentials.

History and physical examination (BTS/SIGN and NICE)

Note that there are no major disparities between BTS/SIGN and NICE recommendations on history-taking and physical examination findings.

Take a careful, structured history.[1][55][56] Specifically check for:[55][56]

  • Key symptoms, which include more than one of the following: wheeze (audible on auscultation), breathlessness, chest tightness, and cough.[1]

    • Symptoms tend to occur in recurrent episodes (attacks), with periods of no (or minimal) symptoms between episodes.[1][55]

    • There is typically evidence of diurnal variability of symptoms (worse at night or in the early morning).[1][55] People with more severe asthma tend to have night-time symptoms, waking them up from sleep.

    • In severe exacerbations, patients are continuously short of breath and may use accessory muscles of respiration. See Acute asthma exacerbation in adults.

  • Triggers

    • Identify factors that worsen the patient's asthma: for example, episodes may be exacerbated by exposure to irritants such as tobacco smoke or fumes from chemicals such as bleach.[1] Symptoms may be precipitated by infection (particularly viral), exposure to cold air, or triggered by strong reactions such as hard laughter.[1]​ Emotions such as stress/anxiety may be associated with exacerbation of asthma symptoms, although these are more often a cause of breathing pattern disorder (dysfunctional breathing) in people with asthma.

    • Attacks may occur seasonally or on exposure to allergens in those with atopy.

    • Exercise can also trigger symptoms.[1]

    • Symptoms may be triggered by use of non-steroidal anti-inflammatory drug (NSAID) medication or beta-blockers.[1]

  • Family history of asthma or personal/family history of other atopic conditions[1]

    • A parental history of asthma is a major risk factor for early development of asthma.[1][2]

    • Notable other atopic conditions include atopic eczema/dermatitis, allergic rhinitis.[1]

The patient's historical medical records may provide valuable additional insights, including previous episodes of professionally confirmed wheeze, and past measurements of lung function or response to treatment.

Confirm wheeze on auscultation.[1][55][56] Distinguish wheezing (a continuous, high-pitched musical sound coming from the chest) from other respiratory noises, e.g., stridor or rattly breathing.[55]

  • With more severe asthma, the wheezes may be audible without the use of a stethoscope.

  • Polyphonic, high-pitched expiratory wheezes are typical of asthma.

  • The absence of wheeze does not exclude asthma.[55][56]

Examine the nasal passages; this may reveal nasal polyposis or nasal congestion.[1]

Bear in mind that the examination may be normal in patients with bronchial asthma.

  • If the patient's chest is repeatedly normal on examination when they are symptomatic, this reduces the likelihood of asthma.[55]

Expiratory wheeze
Expiratory wheeze

Auscultation sounds: Expiratory wheeze

Polyphonic wheeze
Polyphonic wheeze

Auscultation sounds: Polyphonic wheeze

Investigations: overarching principles (BTS/SIGN versus NICE)

The key area where BTS/SIGN recommendations differ from NICE recommendations relates to the role of investigations in the asthma diagnostic pathway. Although BTS/SIGN recognise that objective tests influence the probability of asthma, they recommend that tests alone are not used to confirm the diagnosis and that in some cases a diagnosis can be confirmed without spirometry or fractional exhaled nitric oxide (FeNO) testing.[55] See Diagnostic flowchart above. By contrast, NICE recommends a FeNO test followed by spirometry for any adult in whom a diagnosis of asthma is being considered based on a typical symptom presentation.[56]

The BTS/SIGN guideline highlights the value of comparing the results of diagnostic tests undertaken while the patient is asymptomatic with those undertaken when the patient is symptomatic. Use this to detect variation over time.[55]

  • Both BTS/SIGN and NICE guidelines agree that there is no single symptom, sign, or test that can categorically determine asthma in adults.

  • However, NICE does not include a specific recommendation about comparing results when the patient is asymptomatic with those when a patient is symptomatic to detect variation in symptoms over time, apart from recommending PEF charting in some patients.[56]

  • Performing objective tests at a time when the patient is asymptomatic may lead to false negative results. A one-off measurement of normal lung function does not exclude asthma (more than half of people with asthma may have normal spirometry).[57][58][59]

For patients with suspected asthma presenting for the first time, it is good practice to always request standard tests in the initial work-up to exclude other pathologies, including:

  • A chest x-ray

  • Full blood count with differential

    • An elevated blood eosinophil count is typically associated with more severe exacerbations and poorer asthma control.[60]

Spirometry and bronchodilator reversibility (BTS/SIGN and NICE)

Spirometry is the investigation of choice for identification of airflow obstruction and reversibility.[55][56] It is usual clinical practice in the UK to arrange spirometry for every patient presenting with suspected asthma.

  • This is in line with NICE guidelines, which specify that you should not use symptoms alone to diagnose asthma, and that you should always use an objective test if you suspect asthma following a structured clinical assessment.[56] NICE recommends FeNO followed by spirometry as essential tests for any adult with asthma symptoms.[56] BDR testing is recommended by NICE if spirometry shows obstruction. NICE advises that PEF monitoring over 2 to 4 weeks may be needed if there is diagnostic uncertainty after FeNO and spirometry.[56]

  • Bear in mind, however, that BTS/SIGN recommend that people who clearly have a high probability of asthma (coded as 'suspected asthma') may start an objectively monitored initiation of treatment (e.g., with PEF, validated questionnaires, and/or spirometry), and subsequently receive a confirmed diagnosis of asthma without necessarily performing spirometry or FeNO.[55] BTS/SIGN guidance does recommend spirometry for any patient assessed as having an intermediate probability of asthma, with BDR testing if airway obstruction is confirmed.[55]

  • Check your local guidance on the indications for spirometry in patients with suspected asthma.

The forced expiratory volume at 1 second (FEV₁) and forced vital capacity (FVC) can be used to demonstrate airflow limitation.

  • Use the lower limit of normal (LLN) for the FEV₁/FVC ratio rather than a fixed FEV₁/FVC ratio of 0.7; LLN is a functionality that is increasingly available through software built into spirometers.[55]

  • Use of a fixed ratio can lead to overdiagnosis of obstruction in adults owing to variability of the ratio with age.[55] In adults over 40 years of age, levels below 70% may be normal and use of a 70% threshold will overestimate obstruction.[55]

  • NICE also recommends using the LLN for diagnosis if available; otherwise, NICE recommends using a fixed FEV₁/FVC ratio of 70%.[56]

Use a BDR test to demonstrate reversibility of airflow obstruction in response to short-acting bronchodilators.

  • BTS/SIGN and NICE agree that in adults with obstructive spirometry, an improvement in FEV₁ of 12% or more in response to beta agonists (or to a treatment trial with corticosteroids), together with an increase in volume of 200 mL or more, is regarded as a positive reversibility test.[55][56]

  • BTS/SIGN further recommend that an improvement of greater than 400 mL in FEV₁ strongly suggests underlying asthma.[55]

Bear in mind that normal spirometry in an asymptomatic patient does not rule out a diagnosis of asthma.[55] The false negative rate of spirometry as a diagnostic test for asthma is at least 50%.[56][57]

Variability in lung function (BTS/SIGN and NICE)

Confirmation of an asthma diagnosis relies on demonstration of airflow variability over short periods of time.[55]

Record PEF as the best of three forced expiratory blows from total lung capacity with a maximum pause of 2 seconds before blowing.[55]

  • The patient can be standing or sitting.

  • Record further blows if the largest two PEFs are not within 40 L/minute.

BTS/SIGN recommend using PEF to estimate variability of airflow from multiple measurements made over 2 to 4 weeks.[55]

  • Increased variability may be evident from twice-daily readings.[55]

  • Bear in mind that although more frequent readings will result in a better estimate, they require improved patient adherence. If available, electronic meters and diaries with time and date stamps can improve adherence and accuracy if recording PEF in paper diaries.[55]

  • PEF variability is usually calculated as the difference between the highest and lowest PEF expressed as a percentage of the average PEF.[61][62][63] However, one study showed that three or more days a week with significant variability was more sensitive and specific than calculating mean differences.[64]

  • Ideally, confirm variability by comparing a PEF recorded when the patient is symptomatic (e.g., during the assessment of an asthma attack) with a PEF when asymptomatic (e.g., after recovery from an asthma attack).[55]

Regard a value of more than 20% variability as a positive test.[55][56]

  • The upper limit of the normal range for variability is around 20% using four or more PEF readings per day.[61][62]

NICE recommends PEF charting over 2 to 4 weeks in the following scenarios:[56]

  • Diagnostic uncertainty after initial assessment and a FeNO test and the patient has either:

    • Normal spirometry or

    • Obstructive spirometry, reversible airways obstruction (positive BDR) but a FeNO level of 39 parts per billion (ppb) or less.

  • Diagnostic uncertainty after initial assessment and the patient has:

    • Obstructive spirometry and

    • Irreversible airways obstruction (negative BDR) and

    • A FeNO level between 25 ppb and 39 ppb.

PEF diaries also have an important role in the ongoing monitoring of asthma control. See Monitoring for more details.

Peak flow measurement animated demonstration
Peak flow measurement animated demonstration

How to use a peak flow meter to obtain a peak expiratory flow measurement.

Spirometry technique and interpretation
Spirometry technique and interpretation

A guide on how to perform and interpret spirometry, including common pitfalls.

Fractional exhaled nitric oxide (BTS/SIGN versus NICE)

Fractional exhaled nitric oxide (FeNO) measurement can be used to find evidence of eosinophilic inflammation.[55][56] FeNO testing is not widely available in primary care in the UK (although arrangements to change this are underway).

  • A positive test provides supportive, but not conclusive, evidence for a diagnosis of asthma. A negative test does not exclude the diagnosis.[55]

  • In corticosteroid-naive adults, a FeNO level of 40 ppb or more is regarded as positive.[55][56] Data from adult patients in secondary care suggest that approximately one in five people with a positive FeNO test will not have asthma (false positives), and conversely one in five people with a negative FeNO test will have asthma (false negatives).[55]

  • Bear in mind that FeNO levels are:[55][68][69][70]

    • Increased in patients with allergic rhinitis exposed to allergen, even without any respiratory symptoms

    • Increased by rhinovirus infection in healthy individuals, but this effect is inconsistent in people with asthma

    • Higher in men and tall people

    • Lower in children

    • Reduced (acutely and cumulatively) in people who smoke cigarettes[56]

    • Reduced by inhaled or oral corticosteroids[56]

    • Increased by consumption of dietary nitrates.

BTS/SIGN and NICE guidelines differ in their recommendations on the role of FeNO testing in diagnosing asthma.

  • BTS/SIGN recommend FeNO testing as an option, if available, for adults with an intermediary probability of asthma and normal spirometry results. In this scenario, a positive FeNO test increases the probability of asthma.[55]

  • By contrast, NICE recommends FeNO as the first-line investigation (along with spirometry) for any adult in whom a diagnosis of asthma is being considered.[56]

Recommendations from international guidelines differ:

  • The American Thoracic Society (ATS) recommends FeNO as a supportive test for asthma diagnosis, stating that it should be performed if equipment is available.[71]

  • The European Respiratory Society (ERS) agrees that FeNO can be used in addition to standard tests to aid diagnosis of asthma.[72]

  • The Global Initiative for Asthma (GINA), however, does not recommend FeNO as a test for ruling in or ruling out a diagnosis of asthma. GINA cites the overlap between FeNO levels among people with and without asthma as the basis for this recommendation. GINA asserts that the main role of FeNO is to guide treatment decisions in patients with severe asthma.[1]

FeNO, when used in combination with sputum eosinophilia, has a high sensitivity and specificity.[55][71][73][74] However, sputum eosinophilia is also not a standard test in primary care in the UK at present. Two Cochrane systematic reviews looking at tailoring asthma therapy to either sputum eosinophils or FeNO levels showed fewer exacerbations in each group, but no significant difference in all other outcomes, including quality of life, FeNO levels, or inhaled corticosteroid dose.[75][76]

Airway hyper-reactivity measures (BTS/SIGN versus NICE)

Direct bronchial challenge tests are the most widely used method of measuring airway responsiveness. They measure response in terms of change in FEV₁ a set time after the patient has inhaled increasing concentrations of bronchoconstrictor (histamine or methacholine).[55] A provocative concentration (PC20) of bronchoconstrictor of 8 mg/mL or less is regarded as positive.[55][56]

BTS/SIGN recommend to consider referring the patient for direct challenge tests if there is no evidence of airflow obstruction on initial assessment and other objective tests are inconclusive but asthma remains an intermediate possibility.[55]

  • The guideline also highlights the potential value of indirect challenge tests such as exercise and inhaled mannitol in assessing variability in lung function.[55] A positive response, e.g., a fall in FEV₁ of greater than 15%, is a specific marker of asthma. Indirect challenges are less sensitive than direct challenges, particularly in patients tested while on treatment.[55][77][78]

NICE recommends a direct bronchial challenge test if there is diagnostic uncertainty after a normal spirometry and either a:[56]

  • FeNO level of 40 ppb or more and no variability in PEF readings or

  • FeNO level of 39 ppb or less with variability in PEF readings.

NICE recommends to consider a direct challenge test with histamine or methacholine in people with all of the following:[56]

  • Obstructive spirometry without BDR

  • A FeNO level between 25 ppb and 39 ppb

  • No variability in PEF readings (less than 20% variability over 2-4 weeks).

NICE does not recommend indirect challenges with exercise as diagnostic tests.[56]

Atopic status (BTS/SIGN and NICE)

Although not recommended as routine diagnostic tests, BTS/SIGN advise using a previous record of skin-prick tests, blood eosinophilia of 4% or more, or a raised allergen-specific immunoglobulin E (IgE) to corroborate a history of atopic status.[55]

  • NICE also does not recommend these as routine diagnostic tests but suggests using skin-prick tests to aeroallergens or specific IgE tests to identify triggers after a formal diagnosis of asthma has been made.[56]

In clinical practice, specific allergen sensitivity screening should be considered to confirm allergy in patients with a history suggestive of an allergic trigger.

If you suspect an occupational cause, see Occupational asthma.

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