When should spirometry be performed in patients aged >5 years with suspected or diagnosed asthma?

When to Perform Spirometry for Asthma

Spirometry should be performed as part of the initial diagnostic work-up in all patients aged ≥5 years with suspected asthma, and it must be obtained before making an asthma diagnosis in this age group. 1

Age-Based Approach to Spirometry

Children ≥5 Years and Adults

• Spirometry is strongly recommended as a first-line test for all patients aged 5-16 years (and by extension, adults) presenting with suspected asthma 1, 2
• The European Respiratory Society specifically states that diagnosis must not be based on symptoms alone in patients ≥5 years without objective testing 2
• Children can reliably perform spirometry starting at age 5 years, with experienced operators obtaining good quality data from the majority of children in this age group 1

Children <5 Years

• Spirometry cannot be reliably performed in children under 5 years due to developmental limitations in following instructions and maintaining effort 2
• For children aged 2-4 years, a therapeutic trial with inhaled corticosteroids is the recommended diagnostic approach when objective testing is not feasible 2

Timing of Spirometry Testing

Initial Diagnostic Work-Up

• Perform spirometry at the first evaluation for any patient ≥5 years with suspected asthma 1, 2
• Measure FEV₁, FVC, and calculate the FEV₁/FVC ratio as baseline parameters 3
• An abnormal result is defined as FEV₁/FVC < lower limit of normal (LLN) or <80%, or FEV₁ < LLN or <80% predicted 1

When Initial Spirometry is Normal

• Normal spirometry does not exclude asthma because spirometry is frequently normal during periods of stable disease or when asthma is well-controlled 1, 3
• Repeat spirometry when the patient is symptomatic, particularly during episodes of wheezing or dyspnea 2, 3
• Serial measurements may be required to capture the variable airflow obstruction characteristic of asthma 1, 3

Bronchodilator Reversibility Testing

• Perform bronchodilator reversibility (BDR) testing in all children with abnormal baseline spirometry (FEV₁ < LLN or <80% predicted and/or FEV₁/FVC < LLN or <80%) 1
• Consider BDR testing even when baseline spirometry is normal if clinical suspicion remains high 1, 3
• Re-measure FEV₁ 15 minutes after administration of 400 μg of a short-acting β₂-agonist 1, 3
• An increase in FEV₁ ≥12% and/or ≥200 mL is considered diagnostic of reversible airflow obstruction 1, 4

Diagnostic Confirmation Requirements

Two Abnormal Tests Required

• At least two abnormal objective test results are required to confirm an asthma diagnosis in patients aged 5-16 years 2, 5
• Acceptable combinations include:
  • Abnormal spirometry + positive BDR 2
  • Abnormal spirometry + elevated FeNO (≥25 ppb) 2
  • Positive BDR + elevated FeNO 2

When Diagnosis Remains Unclear

• If spirometry and BDR are normal but clinical suspicion persists, consider peak expiratory flow rate (PEFR) variability testing with twice-daily measurements for 2 weeks; variability ≥12% suggests asthma 5, 3
• Bronchial challenge testing (methacholine or exercise challenge) should be performed when other objective tests are inconclusive; a PC₂₀ <8 mg/mL on methacholine challenge is diagnostic 3

Critical Pitfalls to Avoid

• Never diagnose asthma based solely on symptom improvement after a therapeutic trial without objective spirometry confirmation 2, 3
• Do not assume a single normal spirometry excludes asthma; the variable nature of the disease requires repeat testing during symptomatic periods 1
• Do not rely on a single abnormal test to confirm diagnosis; at least two objective abnormalities are required 2, 5
• Be aware that inadequate FVC maneuver technique can falsely normalize the FEV₁/FVC ratio, potentially missing asthma diagnoses 1, 3
• Spirometry has low sensitivity (12-52%) but moderate to high specificity (72-93%) for asthma diagnosis, meaning it is better at confirming than excluding the diagnosis 1

Special Circumstances

Acute Exacerbations

• Spirometry can be successfully performed during acute exacerbations in children ≥6 years presenting to the emergency department, and often demonstrates greater degrees of airway obstruction than clinical signs alone 6
• In hospitalized adults with physician-diagnosed asthma or COPD exacerbation, adequate quality spirometry can be obtained in approximately 73% of patients and may help identify overdiagnosis, particularly in obese patients 7

Follow-Up Testing

• Repeat spirometry during supervised step-down of preventer medication to confirm or refute the presence of active asthma 1
• Consider "watchful waiting" with repeat testing when the child is symptomatic if initial tests are normal and the patient is relatively asymptomatic between episodes 2