Understanding Your Spirometry and Lung Function Test Results

Spirometry is the most commonly ordered lung function test in primary care and respiratory medicine. Your GP (Primary Care Physician) may request it to investigate a persistent cough, shortness of breath, or wheezing, to monitor a known condition such as asthma or COPD, or to assess your lungs before surgery. The test itself takes around 15 minutes and involves breathing into a mouthpiece connected to a spirometer — a device that measures airflow and volume. Understanding what your results mean allows you to follow your specialist’s recommendations with clarity and to track your progress over time.

1. What Spirometry Measures and Why It Was Ordered

Spirometry measures two fundamental properties of your breathing: how much air your lungs can move, and how quickly they can move it. This combination reveals whether your airways are narrowed, your lung tissue is stiff or scarred, or your breathing muscles are weak — three very different problems that require very different treatments.

Common reasons your doctor orders spirometry include: a new or persistent cough lasting more than eight weeks, breathlessness on exertion that is out of proportion to your fitness level, recurrent chest tightness or wheezing, a known or suspected diagnosis of asthma or COPD, occupational lung disease monitoring (particularly relevant for workers in dusty or chemical-heavy environments in ASEAN manufacturing and construction sectors), and pre-operative lung assessment before major surgery.

2. The Key Numbers — FVC, FEV1, and the FEV1/FVC Ratio

Your spirometry report will show several values. The three most important are:

• FVC — Forced Vital Capacity: the total volume of air you can exhale after breathing in as deeply as possible. Measured in litres. A result at or above 80 percent of the predicted value for your age, sex, height, and ethnicity is considered normal.
• FEV1 — Forced Expiratory Volume in one second: the volume of air exhaled in the first second of that forced breath. Also measured in litres. A normal result is at or above 80 percent of predicted.
• FEV1/FVC ratio: the proportion of your total exhaled air that comes out in the first second. A ratio of 0.70 or above (70 percent) is normal in adults. This single ratio is the most important number on the report — it is what distinguishes obstructive from non-obstructive patterns.

Your report will show both your actual measured values and the percentage of predicted — for example, “FEV1 78% predicted.” The predicted value is calculated from population data matching your demographic profile. Comparing your result to the predicted value is more meaningful than comparing it to a fixed absolute number.

3. What Your Results Mean — Obstructive, Restrictive, and Normal Patterns

There are three broad interpretation patterns:

Normal pattern: FVC ≥80% predicted, FEV1 ≥80% predicted, FEV1/FVC ratio ≥0.70. A normal spirometry result does not rule out all lung conditions — some disorders affect gas exchange rather than airflow — but it is reassuring for the most common causes of breathlessness.

Obstructive pattern: FEV1/FVC ratio below 0.70, with FEV1 reduced. This means air is leaving the lungs more slowly than expected — the airways are narrowed. Conditions causing this pattern include asthma, COPD, bronchiectasis, and vocal cord dysfunction. If an obstructive pattern is found, your doctor will usually perform a bronchodilator reversibility test: spirometry is repeated 15 minutes after you inhale a bronchodilator medication. Significant improvement (FEV1 increase ≥12% and ≥200 mL) supports asthma rather than COPD.

Restrictive pattern: Low FVC with a normal or elevated FEV1/FVC ratio. The lungs cannot fully expand — not because the airways are blocked, but because the lung tissue, chest wall, or breathing muscles are limiting volume. Causes include pulmonary fibrosis, sarcoidosis, severe obesity, pleural disease, and neuromuscular conditions. A restrictive pattern on spirometry usually prompts further testing including a full body plethysmography (body box) to confirm true restriction.

Monitoring your peak expiratory flow between clinic visits is valuable for asthma management in particular. A personal peak flow meter allows you to track your daily readings at home and identify early deterioration before symptoms become severe — a pattern log to bring to your next appointment is far more informative than a single clinic measurement. (Affiliate link — we may earn a small commission at no extra cost to you.)

4. Other Tests in a Full Lung Function Assessment

Spirometry is often the first test but not always the last. Depending on your results and symptoms, your doctor may also order:

• DLCO (Diffusing Capacity for Carbon Monoxide): measures how efficiently oxygen crosses from the air sacs into the bloodstream. A low DLCO suggests emphysema, pulmonary fibrosis, pulmonary hypertension, or anaemia. It is normal in asthma and simple COPD without emphysema.
• Body plethysmography (body box): measures total lung capacity and residual volume — the air remaining in the lungs after full exhalation. Required to confirm a restrictive pattern identified on spirometry.
• Bronchodilator reversibility test: spirometry before and after a bronchodilator inhaler, as described above.
• Bronchoprovocation (challenge) test: used when asthma is suspected but spirometry is normal — a controlled inhaled stimulus is used to provoke a temporary, monitored airway response.
• Six-minute walk test: assesses functional exercise capacity and oxygen desaturation during exertion — commonly used in COPD and pulmonary fibrosis management.

5. What Happens After an Abnormal Spirometry Result

An abnormal result does not mean a diagnosis has been confirmed — it means your doctor now has objective data to work with. The next steps depend on the pattern found:

For an obstructive pattern, your doctor will correlate the spirometry findings with your symptoms, smoking history, age, and any allergy history to distinguish between asthma and COPD. A chest X-ray is typically ordered. If COPD is confirmed, the severity is graded using the GOLD classification based on FEV1 percentage predicted: GOLD 1 (mild, FEV1 ≥80%), GOLD 2 (moderate, 50–79%), GOLD 3 (severe, 30–49%), and GOLD 4 (very severe, below 30%). This grading directly determines the treatment intensity recommended.

For a restrictive pattern, further testing including a body box and CT scan is usually arranged before a definitive cause is established. Referral to a pulmonologist is standard for any restrictive pattern requiring investigation.

If your results are borderline or difficult to interpret, repeat spirometry may be requested — effort and technique significantly affect spirometry accuracy, and a suboptimal test effort can produce a falsely abnormal result.

6. Tracking Your Lung Health Between Appointments

For patients with a confirmed respiratory diagnosis, home monitoring between clinic visits provides your doctor with the trend data that matters most — single clinic readings miss day-to-day variation entirely.

A pulse oximeter is one of the most practical home monitoring tools for anyone with a lung condition. It clips onto your fingertip and measures your blood oxygen saturation (SpO2) and pulse rate in seconds. A normal resting SpO2 is 95 percent or above for most adults. Regular readings give you a baseline and allow you to detect early deterioration — for example, SpO2 dropping below 92 percent at rest is a threshold that most respiratory guidelines recommend as a trigger for seeking urgent review. A reliable device such as the Wellue fingertip pulse oximeter stores recent readings and is straightforward to use daily. (Affiliate link — we may earn a small commission at no extra cost to you.)

For asthma specifically, a peak flow diary kept over two to four weeks — recording morning and evening readings — is often requested by respiratory specialists to assess variability and guide treatment step-up or step-down decisions.

7. Regional Notes — Singapore, Australia, and the United States

Singapore: Spirometry is available at polyclinics under the Chronic Disease Management Programme (CDMP) for patients with asthma or COPD. Subsidised rates apply for eligible Citizens and PRs. The Singapore Lung Cancer Lung Health Initiative and HPB smoking cessation programmes are relevant for patients whose spirometry reflects smoking-related lung disease. Occupational lung disease is reportable under the Work Injury Compensation Act — workers in relevant industries should mention their occupational history explicitly at their GP visit.

Australia: Spirometry is a Medicare-rebated test when ordered by a GP or specialist. The Lung Foundation Australia (lungfoundation.com.au) provides patient resources and a COPD management support programme. Patients diagnosed with COPD may be eligible for a GP Management Plan and Team Care Arrangement, providing subsidised access to physiotherapy and pulmonary rehabilitation.

United States: Spirometry is covered under most insurance plans when ordered for a specific indication. The American Lung Association’s COPD programme and LUNG FORCE initiative provide patient education resources. Medicare covers spirometry for COPD diagnosis. Patients with occupational lung disease exposure may have access to additional monitoring programmes through NIOSH (National Institute for Occupational Safety and Health).

Medical Disclaimer: This guide is for preparation and educational purposes only. It does not constitute medical advice, diagnosis, or treatment. Always follow the guidance of your qualified healthcare provider. If you are experiencing a medical emergency, call your local emergency number immediately (Singapore: 995 | Australia: 000 | New Zealand: 111 | USA/Canada: 911). Full disclaimer →