Why Spirometry Alone Cannot Assess Adequacy of Inhaled Corticosteroid Therapy in Children with Asthma
Spirometry cannot be used alone to assess the adequacy of inhaled corticosteroid therapy in children with asthma because it frequently remains normal even when significant airway inflammation persists, and it fails to capture the multiple dimensions of asthma control including symptom burden, exacerbation risk, and quality of life. 1
The Fundamental Limitation: Normal Spirometry Despite Active Disease
Children with well-controlled asthma on adequate inhaled corticosteroid therapy often have completely normal spirometry, making it impossible to distinguish between adequate treatment and undertreated disease based on lung function alone. 1
Spirometry has very low sensitivity (0.12-0.52) for detecting asthma, meaning that normal values do not exclude ongoing airway inflammation or inadequate disease control. 2
Up to 49% of children with good symptom control (ACT >19) have abnormal spirometry or FeNO, while conversely, many children with poor control have normal spirometry, demonstrating the disconnect between lung function and clinical status. 1
Asthma Control Requires Assessment Beyond Airflow Obstruction
Symptom control measures (such as the Asthma Control Test) are superior to spirometry for predicting future unplanned healthcare attendances and exacerbations in children. 1
Risk factors for poor outcomes—including previous attacks, poor adherence, excessive short-acting beta-agonist use, poor inhaler technique, and comorbid food allergy—must be actively identified and cannot be detected by spirometry. 1
The goal of inhaled corticosteroid therapy is to suppress airway inflammation, improve quality of life, prevent exacerbations, and reduce mortality—outcomes that spirometry alone cannot measure. 3, 4
The Variable Nature of Asthma Makes Single Measurements Unreliable
Asthma is characterized by intermittent symptoms and reversible airflow obstruction, so spirometry performed when the child is asymptomatic or well-controlled will typically be normal, requiring repeated testing on multiple occasions to demonstrate abnormalities. 1, 2
Serial spirometry measurements may be required to capture variable airflow obstruction, particularly if testing occurs between symptomatic episodes, making single assessments inadequate for monitoring. 2
What Should Be Used Instead: A Multi-Dimensional Approach
Primary Assessment Tools
Validated symptom control questionnaires (ACT or cACT) should be the primary tool for assessing therapy adequacy, as they correlate better with future exacerbations than spirometry. 1
Active identification and documentation of risk factors (previous severe attacks, medication adherence, inhaler technique, trigger exposures) must be performed at every review. 1
Fractional exhaled nitric oxide (FeNO) ≥25 ppb can identify persistent eosinophilic airway inflammation despite normal spirometry, indicating inadequate anti-inflammatory control. 1
When to Use Spirometry
Spirometry is valuable for confirming the diagnosis initially (demonstrating reversible airflow obstruction with bronchodilator response ≥12%), but not for routine monitoring of therapy adequacy. 1
Spirometry should be performed if symptoms worsen or control deteriorates to assess for fixed airflow obstruction or alternative diagnoses, but not as a routine measure of treatment success. 1
Common Pitfalls to Avoid
Do not assume adequate therapy based solely on normal spirometry—this misses children with ongoing inflammation who remain at risk for exacerbations. 1, 2
Do not increase inhaled corticosteroid doses based only on abnormal spirometry without assessing adherence, inhaler technique, and environmental trigger control first. 1
Do not use spirometry as the sole endpoint for stepping down therapy—symptom control, exacerbation history, and inflammatory markers (FeNO) must also guide decisions. 1
The Evidence on Inhaled Corticosteroid Effects
Inhaled corticosteroids suppress airway inflammation and reduce exacerbations, but these benefits occur even when spirometry remains normal throughout treatment. 3, 4
The CAMP study demonstrated that inhaled corticosteroids provide excellent asthma control and safety in children, but found no progressive decline in lung function in either treated or untreated groups, proving that spirometry changes do not reflect treatment adequacy. 1
Routine asthma reviews that rely only on spirometry without active risk factor identification fail to predict future poor outcomes, as demonstrated in multiple studies of preventable asthma deaths. 1