2026 UK comparison: FeNO vs spirometry for monitoring airway inflammation in smokers who switch to vaping — when to use each test and the case for home monitoring

Introduction

As vaping overtakes smoking in Great Britain in 2026, clinicians and primary care teams increasingly need clear, practical pathways to monitor respiratory health in people who have switched from cigarettes to e‑cigarettes. Two objective tests dominate current UK practice: fractional exhaled nitric oxide (FeNO) and spirometry. They measure different aspects of airway disease, and both are endorsed by UK guidance and primary care consensus (BTS/NICE/SIGN pathways and Asthma + Lung UK) as complementary tools for diagnosis and monitoring.

Feature-by-feature comparison: FeNO vs spirometry

Feature	FeNO (exhaled nitric oxide)	Spirometry (FEV1, FVC, ratios)
What it measures	Airway eosinophilic inflammation (exhaled NO) — a biomarker linked to steroid responsiveness.	Lung function / airflow obstruction (volumes and flow rates) — objective measure of obstruction and reversibility.
Typical clinical use	Detect eosinophilic inflammation, predict inhaled steroid response, monitor inflammatory trends.	Diagnose and quantify obstruction (COPD/asthma), monitor lung function over time, assess bronchodilator response.
Effort dependence	Non‑effort dependent — simple controlled exhalation; repeatable for trends.	Effort dependent — quality depends on technique, coaching and patient effort.
Typical numeric thresholds	Low: <25 ppb (minimal eosinophilic inflammation). Values >30 ppb often linked to uncontrolled eosinophilic inflammation.	Interpreted relative to predicted values; FEV1/FVC ratio and reversibility guide diagnosis and management.
Variability and timing	Can vary day‑to‑day with exposure and treatment — good for trend monitoring.	May be normal between symptomatic episodes; single readings can miss intermittent disease.
Influences	Smoking acutely suppresses FeNO, so readings in current smokers can underestimate eosinophilia; steroid use raises FeNO response predictability.	Technique, effort, acute symptoms, bronchodilator use and coexisting disease influence results.

Key takeaways from UK guidance and recent 2026 research

UK guidance and consensus pathways (BTS/NICE/SIGN and patient bodies such as Asthma + Lung UK) recommend using both tests as complementary objective measures. Recent 2026 pilot programmes in the UK have trialled home FeNO devices (for example, NObreath in pilot studies) and home spirometry devices (such as the MIR Spirobank Smart), finding that longitudinal home FeNO monitoring can better capture variable eosinophilic inflammation than a single clinic measurement. NHS‑compatible devices and apps with remote coaching are also being trialled to reduce secondary‑care referrals and to support people transitioning from smoking to vaping.

Pros and cons — side‑by‑side

• FeNO — Pros: quick, non‑effort dependent, repeatable at home, specific for eosinophilic inflammation and steroid responsiveness, useful for guiding inhaled corticosteroid decisions.
• FeNO — Cons: suppressed by cigarette smoking (can give falsely low readings in current smokers), less useful for detecting fixed airflow obstruction (COPD), cost and availability of devices if not provided via clinic programmes.
• Spirometry — Pros: gold standard for measuring airflow obstruction, indispensable for diagnosing COPD and monitoring FEV1 trends, widely available in primary care and secondary care.
• Spirometry — Cons: effort dependent and technique sensitive, single tests can be normal between exacerbations, more difficult to perform reliably at home without coaching.

When to use each test — practical recommendations for people switching from smoking to vaping

• Baseline assessment (before or soon after switch): perform both spirometry and FeNO where possible. Spirometry establishes airflow status and reversibility; FeNO gives a baseline of eosinophilic inflammation (bearing in mind smoking may suppress FeNO).
• Early follow‑up (first 3 months): monitor symptoms and consider repeat FeNO monthly if resources allow — symptom improvement may be noticeable by ~3 months, but inflammation can lag.
• Medium term (3–12 months): repeat spirometry at 3–6 months to track lung function changes, and FeNO periodically to document falling eosinophilic inflammation. Emerging 2026 data suggest airway inflammation improvements can take up to ~1 year to appear, so longitudinal monitoring is essential.
• Suspected steroid responsiveness or worsening symptoms: prioritise FeNO to help decide inhaled corticosteroid initiation or adjustment; use spirometry with bronchodilator testing if obstruction or fixed airflow limitation is suspected.
• Remote or home monitoring: use home FeNO (for trends in eosinophilia) and, where available and validated, home spirometry (for FEV1 trends). Virtual coaching and NHS‑compatible apps improve data quality and reduce unnecessary clinic visits.

How often should tests be done?

There is no one‑size‑fits‑all schedule, but a pragmatic approach for someone switching from smoking to vaping is: baseline (both tests), FeNO monthly for the first 3–6 months (or symptom‑triggered), spirometry at 3 and 12 months or sooner if symptoms persist or worsen. Tailor frequency to baseline severity, comorbidities and local pathway resources.

The case for home monitoring

Home monitoring answers two big problems: variability and access. FeNO's non‑effort dependent nature makes it well suited to frequent home checks and trend analysis; pilot programmes in 2026 found home FeNO captured fluctuations that single clinic visits missed. Home spirometry, paired with app‑based coaching and quality checks, can track meaningful FEV1 decline between clinic visits and flag those who need in‑person assessment. Together they create a fuller remote picture for clinicians supporting smoking‑to‑vaping transitions.

Practical notes for patients and clinicians

• Smoking can suppress FeNO — interpret low FeNO with caution in current smokers or recent ex‑smokers.
• Home devices should be NHS‑compatible or validated; data integration into primary care records is ideal.
• For people choosing vaping as a harm‑reduction strategy, offer routine objective monitoring and clear timelines: expect symptom change within ~3 months but allow up to ~12 months to document inflammatory improvement.
• Where patients prefer vaping products or nicotine‑free options, ensure harm‑reduction conversations remain non‑judgemental — for example, nicotine‑free shortfills are an option for those aiming to eliminate nicotine entirely (see non‑nicotine options like 0mg Bar Liq Shortfill 120ml), and for those using e‑cigarettes, low‑maintenance cartridges can be a practical choice (for example, Ezee tobacco cartridges).

Conclusion

FeNO and spirometry are not competitors but partners. FeNO excels at detecting and tracking eosinophilic inflammation and guiding steroid therapy, while spirometry quantifies airflow limitation and is essential for diagnosing COPD and monitoring lung function. UK guidance supports using both tests, and 2026 pilot programmes show that home monitoring — especially longitudinal FeNO — adds valuable information for people who switch from smoking to vaping. A pragmatic pathway combines baseline clinic testing with regular home FeNO checks and interval spirometry, tailored to symptoms, comorbidity and local resources. That blended approach gives clinicians and patients the best chance of tracking recovery from smoking‑related airway disease over the first crucial year after switching.