Approach

The initial assessment of suspected asthma is focused on the presence of key features in the history, clinical examination, and medical records, together with careful consideration of risk factors and alternative diagnoses.[1][98]​ A probability-based approach plus a therapeutic trial is recommended for children 5 years and younger because most will be unable to perform lung function tests reliably. Children 6 years and older should have their asthma diagnosis confirmed with a test of variable expiratory airflow limitation.[1][99][100]​ Although the peak expiratory flow (PEF) is less reliable than spirometry, its use is recommended where diagnosis would otherwise rely on symptoms only.[1]

Definitive diagnosis requires a history of reversible airway obstruction and symptom improvement with inhaled bronchodilators or corticosteroids. See Diagnostic criteria for more information.The basis of an asthma diagnosis or treatment decision should be clearly documented.[1][8]​​ See Acute asthma exacerbation in children for more information about the diagnosis of acute exacerbations.

History

Recurrent symptoms of wheezing, cough (worse at night or early morning), and shortness of breath in response to recognised triggers (e.g., temperature change, viral infection, exercise, and emotion) are characteristic of asthma. Parental perception should be checked because various respiratory noises may be incorrectly labelled as wheezing (where possible, wheeze should be confirmed by a healthcare professional).[101]​ The diagnosis is supported by features of atopic disease, such as eczema, atopic dermatitis, and allergic rhinitis in the child or first-degree family members.

Features associated with asthma include

  • Episodic symptoms (wheeze, breathlessness, chest tightness, and cough occurring episodically with periods of no or minimal symptoms)

  • Wheeze confirmed by a healthcare professional

  • Diurnal variability (worse at night or early morning)

  • A history of atopy

  • Recurrent events over time

Cough is often misdiagnosed as asthma in children, and requires a careful review of the history and the exclusion of alternative causes (see Differentials).[102]

Many children younger than 5 years present with recurrent wheezing due to frequent upper respiratory tract infections (URTIs).[1] Wheeze is a heterogeneous phenotype in young children, and many non-atopic children who experience recurrent episodes of viral-induced wheezing will not require a regular ICS or go on to develop chronic atopic asthma.​

Physical examination

Most children have no signs when they do not have an exacerbation. Depending on the symptom pattern, examination may uncover widespread polyphonic wheeze audible on chest auscultation and respiratory distress (e.g., tachypnoea, recessions or retractions, and accessory muscle use). In poorly controlled persistent asthma, hyperinflation (reflecting gas trapping) and chest wall deformity (Harrison's sulci) may be present. Features of atopic disease may be evident on examination.

Expiratory wheeze
Expiratory wheeze

Auscultation sounds: Expiratory wheeze

Polyphonic wheeze
Polyphonic wheeze

Auscultation sounds: Polyphonic wheeze

Probability-based approach to diagnosis

The greater the variations in expiratory lung function, and the more often excess variation is observed, the more confident a clinician can be with the diagnosis of childhood asthma.[1] However, it is important to ensure that apparent variability does not reflect variations in technique over time, because both spirometry and PEF measures are effort-dependent. The following probability-based approach to diagnosis is proposed.[8][103]​​​

  • High probability of asthma: start with a therapeutic trial and reserve further testing for those with a poor response.

  • Intermediate probability of asthma (can perform spirometry and has evidence of airway obstruction): offer a reversibility test and/or time-limited therapeutic trial.

    • If there is reversibility, or if treatment is beneficial, treat as asthma.

    • If there is no significant reversibility, and/or a therapeutic trial is not beneficial, consider tests for alternative conditions.

  • Intermediate probability of asthma (can perform spirometry and with no evidence of airway obstruction): consider testing for atopic status, bronchodilator reversibility, and, if possible, bronchial hyper-responsiveness using methacholine or exercise.

  • Intermediate probability of asthma (unable to perform spirometry): consider testing for atopic status and offering a time-limited therapeutic trial.

    • If beneficial, treat as asthma.

    • If not beneficial, stop treatment and consider an alternative diagnosis and/or specialist referral.

  • Low probability of asthma: consider more detailed investigation (particularly for other diagnoses) and specialist referral.

The basis on which the diagnosis is suspected should be recorded. Using a structured questionnaire can help standardise this approach, but reliance on asthma prediction tools and screening aids is not recommended because they show wide variation in performance when assessing future risk.[104][105][106][107]​ The Childhood Asthma Risk Tool (CHART) has been proposed; its performance in clinical care remains unclear.[108]

Response to medication

Response to a therapeutic trial of inhaled beta-2 agonist or corticosteroid, given as either a short course of oral corticosteroid (e.g., 1-2 mg/kg/day for 3 days) or a longer trial of low-dose inhaled corticosteroid (e.g., for 4-6 weeks), is suggestive of asthma.[1][8]​​ Any therapeutic trial should be time-limited:

  • Consider a diagnosis of asthma if there is clinical improvement (based on symptom control and exacerbation rate) during treatment and deterioration when treatment is stopped.

  • Consider alternative diagnoses if there is a lack of response; cough and wheeze often have different causes in children than in adults, necessitating care to ensure proper investigation.[102]

This approach is also suitable for children with a non-specific cough and risk factors for asthma.[102][109][110]​​

Spirometry

Spirometry is the preferred method for assessing variability in expiratory lung function. It is performed in children with suspected asthma who are able to give repeatable and reproducible results, but this is highly dependent on local service availability and the child's level of cooperation (typically from age 5 years).[1][111]​ The European Respiratory Society and American Thoracic Society (ERS/ATS) have jointly published standardised guidance for performing and interpreting spirometry.[112][113]​ There are three core spirometry measurements:

  • Forced expiratory volume in 1 second (FEV₁): the total volume of air forcibly exhaled in the first second after one breath. Similar to the PEF.

  • Forced vital capacity (FVC): the total volume of air forcibly exhaled after one breath.

  • FEV₁/FVC: the ratio of FEV1 to FVC expressed as a percentage.

Spirometry technique and interpretation
Spirometry technique and interpretation

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

An obstructive pattern may be present, suggested by visual scalloping of the expiratory flow-volume loop. Decreases can be observed in the FEV₁/FVC ratio, FEV₁, or mid-flows (maximal expiratory flow at 25% of FVC [MEF25] or forced expiratory flow between 25% and 75% of FVC [FEF25-75]). The FEV₁/FVC ratio is normally >0.90 in children.[1] FEV₁ and FEV₁/FVC results below the lower limit of normal (LLN) or below 80% of the predicted value are generally considered suggestive of an asthma diagnosis.[1][8][111]​​​​​​ The LLNs for spirometry values are age-, height-, and ethnicity-dependent.[111][112][113]​​​​ False normal FEV₁/FVC ratios are possible with an incorrect technique, irrespective of age, and normal spirometry results do not automatically exclude asthma.[1][111]​​​​

Response to a beta-2 agonist bronchodilator (>12% improvement in the predicted FEV₁) is also suggestive of an asthma diagnosis.[1][111]​ Of note, the ERS/ATS technical standard for routine lung function tests recommends a >10% improvement in the predicted FEV₁ or FVC for diagnosing bronchodilator reversibility consistent with asthma.[113] Lack of response should be interpreted as evidence of an alternative diagnosis.

It is important to ensure that apparent variability does not reflect variations in technique over time, because measures are effort-dependent.

Airway challenge test

Testing is considered in all children able to deliver reproducible spirometry when the diagnosis remains unclear following initial lung function testing.[111]

Direct and indirect challenge tests

Tests are categorised as direct (methacholine, histamine) or indirect (mannitol, hypertonic saline) depending on how they act on airway smooth muscle. The exact criteria for a positive test depend on the agent used: for methacholine, a fall in the FEV₁ of ≥20% from baseline indicates a positive result; for mannitol, a ≥15% fall from baseline indicates a positive result.[1][111]​ Due to the requirement for reproducible spirometry technique, plus the correct inhalation technique with agents such as mannitol, these tests are typically only considered for children aged ≥5 years.

Due to the presence of airway hyper-responsiveness in other chronic respiratory conditions (such as cystic fibrosis), the main value of airway challenge testing may be in its negative predictive value.

Exercise challenge test

Should be considered when exercise-related symptoms are present and the asthma diagnosis cannot be confirmed with first-line tests.[111] Alternative indirect bronchoprovocation tests may also be used, such as the eucapnic voluntary hyperventilation challenge.[114]​ Typically considered in children aged ≥5 years.​[111][115]

GINA considers a decrease in FEV₁ of >12% predicted, or a decrease in peak expiratory flow of >15% from baseline, to be significant and is consistent with a diagnosis of exercise-induced bronchoconstriction.[1] ERS paediatric guidelines state that a decrease in FEV₁ of >10% from baseline constitutes a positive test.[111]

Peak expiratory flow

Measurement of the PEF can be used as an alternative to spirometry where spirometry services are not available. Although the PEF is less reliable than spirometry, its use is preferred where diagnosis would otherwise rely on symptoms only (see Diagnostic criteria).[1] A PEF lower than the age- and height-predicted normal range may be consistent with airway obstruction. However, it is important to ensure that apparent variability does not reflect variations in technique over time, because measures are effort-dependent. PEF criteria that suggest excess variability in expiratory lung function include:[1]

  • Positive bronchodilator responsiveness (≥15%)

  • Excessive diurnal variability in twice-daily measurements (>13%)

  • Improved lung function after 4 weeks of treatment (≥15%)

  • Positive bronchial challenge (fall of <15%)

  • Excessive variation in lung function between visits (≥15%)

In a small proportion of children with poor symptom perception PEF may have a role in ongoing asthma management. However, symptom-based asthma action plans are preferred to guide therapy.[116]

Record the highest of 3 PEF readings.​

Peak flow measurement animated demonstration
Peak flow measurement animated demonstration

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

Other investigations

Other non-routine investigations can help differentiate an asthma diagnosis from other conditions where uncertainty exists.

  • Full blood count: may demonstrate eosinophilia (4% or greater) in asthma patients. No lab test can diagnose asthma.

  • Sweat test: useful when considering cystic fibrosis in the differential diagnosis.

  • Sputum culture: useful when determining bacterial infection.

  • Skin prick testing: may be used to confirm atopy.

  • Electron micrograph ciliary studies: to assess for Kartagener syndrome (primary ciliary dyskinesia and situs inversus with unusually positioned gastric bubble).

  • Bronchoscopy: can inform a diagnosis of foreign body aspiration, bronchomalacia, or tracheomalacia in patients with unilateral wheezing or inspiratory stridor.

  • Bronchoalveolar lavage: may show airway eosinophilia (>1.2%) or sputum eosinophilia (>3%) is supportive, but is not diagnostic, of asthma.[120][121]

  • Chest imaging (x-ray or high-resolution CT): may demonstrate hyperinflation in asthma, can diagnose bronchiectasis and situs inversus, and can distinguish cardiac from pulmonary diseases. Imaging is not recommended routinely to predict treatment outcomes or lung function or to assess treatment response.

  • CT sinus: can show evidence of chronic rhinosinusitis or nasal polyps, which can be used to guide biologic therapy.

Fractional exhaled nitric oxide

Some guidelines state that an elevated fractional exhaled nitric oxide (FeNO) may be used to support a diagnosis of asthma.[100][122] Others consider that there is a lack of evidence to support the routine use of FeNO.[8]​ Clinician-led guidelines agree that FeNO levels are not diagnostic on their own, and GINA states that further studies are still needed to guide recommendations on FeNO use.[1][8][111][122][123][124]

Although FeNO is modestly associated with some markers (sputum and blood eosinophil levels), levels vary depending on a range of patient factors (including age and height), meaning that it cannot be used in isolation to diagnose or exclude asthma. For example, levels are known to be higher in type 2 airway inflammation and some non-asthma conditions (e.g., eosinophilic bronchitis, atopy, allergic rhinitis, eczema); normal in other asthma phenotypes (e.g., neutrophilic asthma); lower in smokers, during bronchoconstriction, and the early phases of an allergic response; and can be either increased or decreased during viral respiratory infections.[1] FeNO levels are also influenced by ethnicity, and to this end, a look-up table has been proposed.[125]

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