Tests
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Astma bij volwassenen: diagnose en monitoring in de eerste lijnPublished by: Werkgroep Ontwikkeling Richtlijnen Eerste Lijn (Worel)Last published: 2020Asthme chez l’adulte : diagnostic et surveillance en soins de santé primairesPublished by: Groupe de Travail Développement de recommmandations de première ligneLast published: 20201st tests to order
FEV₁/FVC ratio
Test
Forced expiratory volume at 1 second (FEV₁)/forced vital capacity (FVC) ratio is the primary diagnostic test.[3]
A bronchodilator reversibility test may be used, which can demonstrate reversibility of airflow obstruction to short-acting bronchodilator, usually defined as improvement in FEV₁ by ≥12% and ≥200 mL from baseline.[3]
Moderate sensitivity and high specificity.
A guide on how to perform and interpret spirometry, including common pitfalls.
Result
FEV₁/FVC <80% of predicted
peak expiratory flow (PEF)
Test
If PEF monitoring is performed, the written asthma action plan should use the patient's personal best PEF as the reference value.
Long-term daily PEF monitoring should be considered for: patients who have moderate or severe persistent asthma; patients who have a history of severe exacerbations; patients who poorly perceive airflow obstruction and worsening asthma; or patients who prefer this monitoring method.
Long-term daily PEF monitoring can be helpful to: detect early changes in disease states that require treatment; evaluate responses to changes in therapy; and afford a quantitative measure of impairment.
PEF monitoring during exacerbations will help determine the severity of the exacerbations and guide therapeutic decisions in the home, school, clinicians' office, or emergency department.[1]
How to use a peak flow meter to obtain a peak expiratory flow measurement.
Result
flow rate as a comparison to patient's personal best or normal values for height and gender
Tests to consider
chest x-ray
Test
Indicated at first presentation to exclude other pathologies, and in acute exacerbations when complicating factors are suspected from history and exam.[120]
May also show signs of infection in acute exacerbation or pneumothorax.
Result
normal or hyperinflated
CBC with differential
Test
Indicated in first presentation and in acute exacerbations when complicating factors are suspected from history and exam.
Useful for identifying eosinophilia and directing biologic therapy.[106][107][108] Blood eosinophil levels may be elevated by a positive skin-prick test, elevated total IgE, current smoking, allergic rhinitis, age ≤18 years, male sex, a COPD diagnosis, metabolic syndrome, and adiposity.[117]
In hypereosinophilia, exclude parasitic infection (count ≥300/μL) and eosinophilic granulomatosis with polyangitis (count ≥1500/μL).
Result
normal or elevated eosinophils and/or neutrophilia
fractional exhaled nitric oxide (FeNO)
Test
Measures airway-specific eosinophilic inflammation.[110] The main US guidelines differ in their guidance and only conditionally recommend FeNO testing.[3][111][112] Levels >20 ppb generally considered evidence of type 2 inflammation.[3]
GINA states that the main role of FeNO is to help guide treatment decisions in patients with severe asthma. They do not recommend FeNO as a test for confirming or excluding a diagnosis of asthma, citing the overlap between FeNO levels among people with and without asthma as the main reason.[3]
The 2020 US National Asthma Education and Prevention Program Coordinating Committee (NAEPPCC) guideline recommends FeNO measurement as an adjunct where the diagnosis of asthma is uncertain after obtaining a detailed history and diagnostic workup, and for ongoing monitoring to determine control in people with persistent asthma (provided FeNO is measured frequently and not interpreted in isolation).[111] Thresholds for low, indeterminate, and high are <25, 25-50, and >50 ppb, respectively.
The American Thoracic Society (ATS) recommend FeNO measurement in all patients with asthma being considered for treatment, stating that FeNO values can be considered alongside other factors (e.g., exacerbation risk) to guide individual treatment decisions.[112] However, they have not established decision-making thresholds.
High levels indicate that eosinophilic airways inflammation is likely, the phenotype is more likely to respond to inhaled corticosteroids (ICS), and that the patient has allergic asthma or eosinophilic asthma.
FeNO also varies with patient factors, being:[3] elevated in patients with airway eosinophilia due to comorbid type 2 inflammatory conditions, such as chronic rhinosinusitis or allergic rhinitis; normal in nonallergic asthma phenotypes (e.g., neutrophilic asthma); lower in smokers, during periods of active bronchoconstriction, and the early phases of an allergic response; and either increased or decreased during viral respiratory infections. In patients using corticosteroids, FeNO is generally lower in adherent than in nonadherent patients.[113]
Two Cochrane systematic reviews evaluating asthma therapy tailored to either sputum eosinophils or FeNO levels reported fewer exacerbations in both groups, but without significant differences in other outcomes, including quality of life, FeNO levels, or inhaled corticosteroid dose.[115][116]
Result
results vary between analyzers and between local, national, and international guidelines; generally, low if <25 ppb, intermediate if 25-50 ppb, and high if >50 ppb; note that clinical trials have typically considered levels >20 ppb as evidence of type 2 inflammation
bronchial challenge test
Test
May be considered if spirometry and peak expiratory flow rate do not show reversibility and variability.
Challenge tests to diagnose asthma are divided into: direct (using agents that directly constrict airway smooth muscle (i.e., histamine or methacholine) and indirect (methods or agents that activate mast cells to release mediators such as histamine and leukotrienes to constrict airway smooth muscle: e.g., exercise, eucapnic hyperventilation, inhaled hypertonic saline, mannitol, or adenosine monophosphate) challenges. These direct and indirect challenges reflect the baseline fixed (airway remodeling) and episodic variable (inflammatory) components of airway hyperresponsiveness, respectively.[102]
Challenge tests are more resource-intensive than those such as the bronchodilator reversibility test.[98]
Result
positive
serum radioallergosorbent test (RAST) immunoassay for allergen-specific IgE
Test
Can identify sensitivity to allergens (i.e., modifiable risk factors) and help direct biologic immunotherapy (i.e., omalizumab) as part of a comprehensive review.[3][106][107][108]
Consider when there is a possible allergic component and a consistent patient history of atopy (e.g., reported sensitivity to aeroallergens, allergic rhinitis, suspected food allergy, anaphylaxis).[3]
If allergy is not present, there is no need to consider anti-allergy measures.
Increased baseline total and allergen-specific serum IgE levels appear to be common products of the type 2 inflammation pathway, but they have not demonstrated strong predictive ability for either airway eosinophilia or response to biologic treatment in allergic or eosinophilic disease.[106][107][108][109]
Result
positive for allergen; check local guidelines for diagnostic thresholds
skin-prick allergy testing
Test
Can identify allergens (i.e., modifiable risk factors) and help direct biologic immunotherapy (i.e., omalizumab) as part of a comprehensive review. Performed by an allergist in clinic. Similar sensitivity to radioallergosorbent test (RAST) allergy testing.[3][106][107][108]
Consider when there is a possible allergic component and a consistent patient history (e.g., persistent asthma, comorbid allergic rhinitis, suspected food allergy, or anaphylaxis).[3]
If allergy is not present, there is no need to consider anti-allergy measures.
Result
positive for allergen
high-resolution CT (HRCT) chest
Test
Not recommended routinely either to predict treatment outcomes or lung function or to assess treatment response.[120]
May be performed to exclude alternative pulmonary and cardiac causes of dyspnea (e.g., bronchiectasis).[120] In asthma, HRCT typically demonstrates mosaic lung attenuation and air trapping on expiration.[120]
Result
normal or may show hyperinflation, bronchiectasis
CT sinus
Test
CT sinus can show evidence of chronic rhinosinusitis and nasal polyps, which are associated with more severe asthma.
The presence of chronic rhinosinusitis with nasal polyposis can also help identify candidates for biologic therapy.[121][122]
Not recommended routinely.
Result
normal or may show opacification of involved sinuses, mucosal thickening, air-fluid levels, or anatomic abnormalities such as polyps
Emerging tests
sputum eosinophil count
Test
Increased with type 2 inflammation, but shows low ability to differentiate patients.[107]
Reflects the level of inflammation in the airway and the response to inhaled corticosteroid.
Limited by the patient's ability to produce sputum after induction.
A combination of FeNO and sputum eosinophilia has a high specificity and sensitivity.
Repeat test in follow-up.
Not commonly done. Only a limited number of centers have facilities to routinely analyze induced sputum.[3] No comparative data available on sputum eosinophilia versus FeNO.
Result
increased; considered evidence of type 2 inflammation if >2%
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