01OverviewDefinition, clinical context and the essential points that orientate the chapter.
The central diagnostic task is to connect a characteristic pattern of variable symptoms to objective evidence of airway inflammation, variable airflow or bronchial hyperresponsiveness, while actively testing credible alternatives. Overdiagnosis exposes people to unnecessary treatment; underdiagnosis leaves preventable exacerbation risk.
NG245's adult sequence reflects imperfect tests: eosinophils and FeNO are specific markers of type 2 inflammation in context, reversibility captures variable obstruction, PEF captures variability over time, and bronchial challenge can clarify persistent uncertainty. Negative results are interpreted in sequence rather than used as isolated exclusions.
Phenotyping becomes most important when asthma is difficult to control or severe. It should follow confirmation, adherence and inhaler-technique review because apparent 'severe asthma' is often uncontrolled for remediable reasons.
Key points
- Asthma is a clinical syndrome of variable respiratory symptoms and variable expiratory airflow limitation; neither symptoms nor a single test is sufficient in every patient.
- Typical variability includes episodic wheeze, breathlessness, chest tightness or cough that changes over time and with triggers, nights, seasons, work or treatment.
- Before testing, document recent inhaled corticosteroid because it can suppress eosinophils, FeNO and reversibility and make objective confirmation harder.
- For adults with a suggestive history, NG245 begins objective confirmation with blood eosinophil count or FeNO; eosinophils above the laboratory reference range or FeNO at least 50 ppb can confirm asthma in the right context.
- If not confirmed, use bronchodilator reversibility: FEV1 rise at least 12% and 200 mL, or at least 10% predicted FEV1.
- If spirometry is unavailable or delayed, twice-daily PEF variability at least 20% over 2 weeks supports diagnosis; persistent uncertainty may require bronchial challenge or specialist review.
- A normal examination, spirometry or FeNO does not exclude intermittent asthma; repeat testing when symptomatic and review treatment effects.
- Ask every adult with new or recurrent asthma about occupation. Improvement away from work needs serial work/rest-day PEF and early occupational-respiratory referral, not advice to resign before assessment.
- Phenotypes—type 2/eosinophilic, allergic, exercise-related, obesity-associated, aspirin/NSAID-exacerbated or occupational—inform risk and specialist therapy but can overlap and change.
- Never prescribe SABA monotherapy for asthma; once confirmed, use an ICS-containing pathway and a personalised action plan.
02AetiologyUnderlying causes, associations and risk factors, with why each one matters.
Atopic susceptibility
Inherited tendency to type 2 inflammation, often accompanied by rhinitis, eczema or allergen sensitisation, increases the likelihood of variable airway inflammation and bronchial hyperresponsiveness.
Environmental exposures
Tobacco smoke, air pollution, indoor allergens and respiratory infections can initiate or amplify symptoms in a susceptible airway, although an apparent trigger alone does not establish asthma.
Work-related sensitisation
Flour, isocyanates, laboratory animals and other occupational agents may cause new sensitiser-induced asthma or worsen pre-existing disease, making the temporal relationship with work clinically important.
Non-type 2 pathways
Some adults have obesity-associated, irritant-related or paucigranulocytic disease without prominent eosinophilia, reflecting heterogeneous mechanisms rather than a single inflammatory phenotype.
03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.
- 1Airway inflammation
Inflammatory cells and mediators activate the bronchial mucosa, producing oedema, mucus secretion and heightened sensitivity to otherwise modest physical or chemical stimuli.
- 2Variable narrowing
Airway smooth muscle contracts episodically while mucosal swelling and mucus further reduce calibre, causing variable expiratory airflow limitation that may improve spontaneously or after bronchodilation.
- 3Ventilation mismatch
Patchy obstruction creates uneven ventilation relative to perfusion, explaining hypoxaemia during severe attacks and the changing pattern of wheeze, cough and breathlessness.
- 4Airway remodelling
Repeated or persistent inflammation can thicken the airway wall and increase smooth-muscle mass, leaving some people with less reversible obstruction despite a history of variable disease.
04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.
Symptoms vary by time and intensity, are triggered by viral infection, allergen, exercise, cold air or irritants, and may worsen at night/early morning. Examination can be normal between episodes.
Raised blood eosinophils, FeNO, atopy, nasal polyps or steroid responsiveness suggests type 2 inflammation. Values are affected by ICS, smoking, infection and comorbidity and should not be treated as a stand-alone severity score.
New adult-onset asthma or recurrence linked to workplace exposure, with improvement on days away or holidays. High-risk work includes baking, spray painting, laboratory animal work, healthcare sensitising agents and some manufacturing.
Asthma with chronic rhinosinusitis/nasal polyps and reproducible respiratory reactions to aspirin or other COX-1 NSAIDs. Avoid unsupervised challenge and refer when diagnosis or analgesic options are uncertain.
05InvestigationsWhat to request, why it matters and how to interpret it.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Structured history and examinationFirst step - Why
- Estimate pre-test probability and identify urgency, triggers, risk and alternatives.
- Interpretation and limitations
- Document variability, nocturnal symptoms, atopy, rhinitis/polyps, smoking/vaping, medicines, occupation, exacerbations, steroid courses, admissions and family history. Wheeze absence does not exclude asthma.
- 02
Blood eosinophil count or FeNO - Why
- Identify objective type 2 inflammation early in the NG245 adult sequence.
- Interpretation and limitations
- Eosinophils above the laboratory reference range or FeNO at least 50 ppb can confirm asthma in a compatible presentation. A lower value does not exclude it; ICS can suppress both and rhinitis can raise FeNO.
- 03
Spirometry with bronchodilator reversibility - Why
- Demonstrate airflow obstruction and variability.
- Interpretation and limitations
- FEV1 rise at least 12% and 200 mL from baseline, or at least 10% predicted FEV1, supports adult asthma. Normal baseline spirometry is common between episodes.
- 04
Twice-daily PEF for 2 weeks - Why
- Capture variability when spirometry is unavailable/delayed or symptoms are intermittent.
- Interpretation and limitations
- Mean diurnal variability at least 20% supports asthma. Use the same meter and verified technique; fabricated or selectively recorded diaries are unreliable.
- 05
Bronchial challenge - Why
- Assess airway hyperresponsiveness when diagnosis remains uncertain after other objective tests.
- Interpretation and limitations
- Specialist methacholine, histamine or mannitol testing can support diagnosis; contraindications and medicine withholding require a formal protocol.
- 06
Serial work and rest-day PEF - Why
- Evaluate suspected occupational asthma without prematurely ending exposure.
- Interpretation and limitations
- Frequent readings across work and non-work periods with symptom/exposure diary are interpreted by an occupational-respiratory service; early referral improves the chance of establishing causality.
- 07
Targeted alternatives - Why
- Investigate competing or coexisting diagnoses.
- Interpretation and limitations
- Choose CXR, ECG/BNP/echo, CTPA pathway, full lung function, CT, laryngoscopy or reflux/rhinitis assessment based on red flags and the clinical pattern rather than ordering every test routinely.
06Differential diagnosisRealistic alternatives and the features that help distinguish them.
Chronic obstructive pulmonary disease
Persistent post-bronchodilator obstruction with substantial smoking or exposure history and progressive rather than variable symptoms favours COPD, although both diseases may coexist.
Inducible laryngeal obstruction
Abrupt inspiratory difficulty, throat tightness and stridor, especially during exercise, point towards laryngeal closure; laryngoscopy during symptoms is more discriminating than asthma biomarkers.
Cardiac disease
Orthopnoea, oedema, cardiac signs or congestion on imaging suggest heart failure, while palpitations and episodic symptoms may indicate an arrhythmia rather than bronchoconstriction.
Bronchiectasis
Daily productive cough, recurrent bacterial infection and characteristic bronchial dilatation on thin-section CT distinguish bronchiectasis from uncomplicated asthma.
Dysfunctional breathing
Disproportionate breathlessness, tingling or sighing with normal objective airflow tests suggests an abnormal breathing pattern after dangerous cardiopulmonary causes have been assessed.
Additional chapter-specific clues
Pulmonary embolism, pneumothorax, acute heart failure, anaphylaxis or central airway obstruction may present with wheeze/breathlessness but need a different emergency pathway.
Inducible laryngeal obstruction, dysfunctional breathing, reflux, rhinitis, obesity/deconditioning, COPD, bronchiectasis or ACE-inhibitor cough can coexist with or imitate asthma.
07ManagementImmediate care, first-line treatment, alternatives and escalation.
01DiagnosisNG245 adult objective sequenceFirst stepHistory suggests asthma and the person is not acutely unstable.+
- 11. Record symptoms, examination, exposures, treatment and alternatives; do not confirm asthma on symptoms alone.
- 22. Measure blood eosinophils or FeNO. In a compatible presentation, eosinophils above the laboratory range or FeNO at least 50 ppb can confirm asthma.
- 33. If not confirmed, perform spirometry with bronchodilator reversibility; use the adult threshold of at least 12% and 200 mL FEV1 increase, or at least 10% predicted.
- 44. If spirometry is unavailable/delayed, use twice-daily PEF for 2 weeks; variability at least 20% supports diagnosis. If tests remain negative but suspicion persists, refer for bronchial challenge or specialist review.
02Already on ICSRecover objective evidence without unsafe withdrawalSuspected asthma but anti-inflammatory treatment may have normalised tests.+
- 1Review the original record for pre-treatment eosinophils, FeNO, spirometry, PEF variability or a clearly documented acute response.
- 2If stable, arrange specialist/experienced review to decide whether and how treatment can be adjusted while symptoms and lung function are monitored; do not stop ICS abruptly in a high-risk patient.
- 3Repeat objective testing at a clinically informative time and actively investigate mimics. If the diagnosis remains uncertain, document uncertainty rather than permanently coding asthma from response alone.
03Work-relatedSuspected occupational asthmaSymptoms improve away from work or follow a recognised sensitiser/irritant exposure.+
- 1Take a job-task-exposure history, timing of symptoms and co-worker cases; ask about both sensitiser-induced disease and high-level irritant events.
- 2Arrange serial PEF at and away from work with the same meter and a contemporaneous exposure/symptom diary, provided this is safe.
- 3Refer early to an occupational-respiratory specialist. Do not advise resignation before objective assessment unless immediate safety requires exposure avoidance; workplace changes have major health and employment consequences.
04Difficult controlConfirm before phenotyping severe diseasePersistent symptoms, repeated attacks or high treatment requirement.+
- 1Reconfirm the diagnosis and assess inhaler technique, adherence, prescription collection, smoking/vaping, triggers and comorbid rhinitis, obesity, reflux or inducible laryngeal obstruction.
- 2Measure objective control/risk: exacerbations, steroid exposure, spirometry and type 2 biomarkers when clinically appropriate; identify fungal sensitisation or vasculitis clues when present.
- 3Refer for specialist severe-asthma assessment when uncontrolled on high-dose therapy, after hospital/near-fatal attack, with diagnostic uncertainty, or when biologic/maintenance oral steroid therapy is being considered.
Key medicines and prescribing safety3 treatments · regimens, roles and cautions+
Budesonide/formoterol anti-inflammatory reliever after diagnosis
Example licensed product: budesonide/formoterol delivered 160/4.5 micrograms, 1 inhalation as needed; if symptoms persist take 1 further inhalation. Not more than 6 on one occasion; more than 8/day is not normally needed and up to 12/day is only for a limited period under the product directions.Product strengths, delivered doses and licences differ—prescribe by specific device and teach technique. Frequent use or poor response requires urgent reassessment. This is not a diagnostic trial in an unstable patient.
Salbutamol for reversibility testing
400 micrograms inhaled through a spacer for diagnostic bronchodilator reversibility, with repeat spirometry after the protocol interval.Do not convert a positive test into SABA-only treatment. Tremor, tachycardia and hypokalaemia can occur; document recent bronchodilator use.
Montelukast when used as a phenotype-relevant add-on
10 mg orally once daily in the evening for adults and adolescents aged 15 years or older; use as a time-limited add-on trial where guideline/specialist pathway supports it.Warn about neuropsychiatric reactions including sleep, mood and behavioural change; stop and seek review if concerning symptoms occur. Assess response and discontinue if ineffective.
08ComplicationsImportant consequences, why they occur and why they matter clinically.
Severe exacerbation
Rapid, extensive airflow obstruction can cause exhaustion, hypoxaemia and ventilatory failure, sometimes with little audible wheeze when airflow becomes critically limited.
Fixed airflow limitation
Long-standing inflammation and structural remodelling may produce persistent obstruction, increasing daily symptoms and complicating distinction from COPD.
Corticosteroid harm
Repeated systemic corticosteroid exposure contributes to osteoporosis, diabetes, adrenal suppression, infection and mood effects, making attack prevention and steroid stewardship important.
Restricted participation
Poorly controlled symptoms can disturb sleep, limit exercise and work, and drive anxiety or avoidant behaviour even when baseline spirometry is preserved.
09Monitoring and follow-upTreatment response, safety checks and longer-term review.
- Record the objective evidence supporting diagnosis, test dates, treatment at the time and any residual uncertainty.
- At review, assess symptom control, attacks, oral steroid courses, urgent care, reliever use, inhaler technique, adherence and a personalised action plan—not symptoms alone.
- Repeat spirometry or PEF when it answers a clinical question: diagnostic uncertainty, unexpected decline, occupational pattern or treatment response.
- Track total corticosteroid exposure and refer when attacks or high-dose requirements persist despite corrected technique/adherence.
- For occupational asthma, preserve serial PEF/exposure records and coordinate workplace advice through an experienced service.
10Special situationsVariants, exceptions and circumstances that change the usual approach.
FeNO is contextual
High FeNO supports type 2 airway inflammation but can reflect rhinitis and is suppressed by ICS or smoking. It is powerful evidence in sequence, not a universal asthma meter.
Phenotypes overlap
An obese adult can still have eosinophilic allergic asthma; a phenotype label should open relevant treatment questions, not close off coexisting biology.
Treatment response is not a clean diagnostic test
Symptoms can improve through placebo effects, natural variability or treatment of a mimic. Wherever possible, pair a treatment trial with objective baseline and follow-up measures.
Occupational timing is perishable evidence
Once exposure stops or treatment intensifies, serial patterns can disappear. Ask early and refer before irreversible employment decisions where safe.
Risk and daily control are different
A person with few interval symptoms but a previous ICU attack remains high risk. Diagnosis and review must capture exacerbation history, not only current wheeze.
11Common pitfallsFrequent interpretation and management errors.
- 01
Coding asthma from wheeze alone without objective confirmation or a plan to obtain it.
- 02
Excluding asthma because examination or spirometry is normal between attacks.
- 03
Ignoring ICS use when interpreting normal FeNO, eosinophils or reversibility.
- 04
Calling every adult smoker with obstruction COPD without considering asthma or coexistence.
- 05
Treating a phenotype biomarker rather than confirming adherence, technique and diagnosis.
- 06
Missing an occupational relationship or advising permanent job loss before specialist assessment.