Spirometry Explained: What the Test Tells Your Doctor About Your Lungs
You have been told to have a spirometry test — or you have received results you do not fully understand. A pulmonologist explains exactly what spirometry measures, what the numbers mean, what conditions it diagnoses, and why this simple breathing test is the most important tool in respiratory medicine.
A patient sits down across from me after their spirometry test, holding a printout with numbers, graphs, and percentages that mean nothing to them. They have been told their results are "abnormal" or "mildly reduced" — and that single phrase has sent them into a spiral of anxiety. They want to know: what does it actually mean? Is it serious? What happens next?
This question comes up in almost every pulmonology consultation I conduct — and the fact that it comes up so often reflects a genuine gap in how test results are communicated to patients. Spirometry is the most fundamental and most widely performed test in respiratory medicine. It is to lung disease what a blood pressure measurement is to cardiovascular medicine — a simple, non-invasive measurement that carries enormous diagnostic and monitoring value. And yet most patients who have it done leave with results they cannot interpret.
This article closes that gap. By the end of it, you will understand exactly what spirometry measures, what the key numbers mean, how results are used to diagnose conditions like asthma and COPD, and what you should do if your results are abnormal.
What Is Spirometry?
Spirometry is a breathing test that measures how much air your lungs can hold and — more importantly — how quickly you can move air in and out of them. It is performed using a device called a spirometer, which measures airflow precisely as you breathe into a mouthpiece. The test takes approximately 10 to 15 minutes, requires no needles or radiation, causes no pain, and can be performed in any pulmonology clinic or well-equipped general practice.
The word "spirometry" comes from the Latin spirare (to breathe) and the Greek metron (to measure). It has been used in clinical medicine since the 1840s — making it one of the oldest diagnostic tests in respiratory medicine — but modern computerised spirometers produce precise, reproducible measurements that have transformed its diagnostic utility.
Spirometry is used for three main purposes: to diagnose respiratory conditions such as asthma, COPD, and pulmonary fibrosis; to assess the severity of known lung disease and track its progression over time; and to monitor the response to treatment — confirming whether a medication or intervention is producing the expected improvement in lung function.
What Happens During the Test?
Understanding the procedure in advance reduces anxiety and — importantly — helps patients perform the test correctly, which directly affects the quality and reliability of the results.
Preparation
Before your spirometry test, your pulmonologist will ask you to avoid using short-acting bronchodilator inhalers (such as salbutamol) for four to six hours beforehand, and long-acting inhalers for 12 to 24 hours, unless the test is specifically being performed while on medication to assess its effect. Avoid heavy meals for two hours before the test, as a full stomach reduces the diaphragm's range of movement. Wear comfortable, loose clothing that does not restrict chest expansion. Do not smoke for at least four hours before testing.
The Test Itself
You will be seated comfortably. A nose clip will be placed on your nose to ensure all airflow passes through the mouthpiece. The technician will ask you to:
- Breathe in as deeply as you possibly can — a maximum inhalation filling every corner of your lungs
- Place the mouthpiece between your teeth and seal your lips tightly around it
- Blast the air out as hard, fast, and completely as you can — like blowing out all the candles on a birthday cake in one enormous breath
- Continue blowing until your lungs are completely empty — which typically takes six seconds or more
This manoeuvre — called a forced vital capacity (FVC) manoeuvre — is repeated at least three times to obtain consistent, reproducible results. It requires maximum effort on every attempt. The technician will coach you enthusiastically through each blow — this is not just encouragement, it is diagnostically important, because a submaximal effort produces falsely low readings that can lead to incorrect diagnoses.
Bronchodilator Reversibility Testing
In many cases, the spirometry will be performed twice — before and after inhaling a bronchodilator medication (usually salbutamol). The before-and-after comparison tells the doctor whether any airflow obstruction present is reversible — which is the key feature distinguishing asthma from COPD — and whether a patient's lung function responds to bronchodilator therapy.
Understanding Your Results — The Key Measurements
Spirometry generates several measurements, but two are central to almost all clinical decision-making: FEV1 and FVC. Understanding what these mean is the foundation of reading a spirometry result.
FVC — Forced Vital Capacity
FVC is the total volume of air you can forcibly exhale after taking the deepest possible breath. It represents the usable capacity of your lungs — the total volume available for breathing. In a healthy adult, the FVC is typically between 3 and 5 litres depending on age, height, and sex.
A reduced FVC indicates that the lungs are holding less air than expected. This can occur because the lungs are physically smaller or stiffer than normal (as in pulmonary fibrosis or other restrictive conditions), because the chest wall or respiratory muscles cannot expand fully, or because the airways are so severely obstructed that not all the air can be expelled even with maximal effort.
FEV1 — Forced Expiratory Volume in One Second
FEV1 is the volume of air you can forcibly exhale in the first second of the FVC manoeuvre. It is the single most important number in spirometry. Healthy adults can exhale approximately 70 to 80 percent of their total FVC in the first second — because healthy, wide-open airways offer minimal resistance to airflow. When airways are narrowed — as in asthma or COPD — air cannot escape as quickly, and a smaller proportion of the FVC is exhaled in the first second. FEV1 is therefore a direct measure of airway patency — how open and unobstructed the airways are.
FEV1/FVC Ratio — The Most Diagnostic Number
The ratio of FEV1 to FVC — expressed as a decimal (e.g. 0.75) or a percentage (e.g. 75%) — is the most diagnostically important value in spirometry. It answers the question: of the total air available to exhale, what proportion can be expelled in the first second?
- A ratio above 0.70 (70%) in adults is generally considered normal
- A ratio below 0.70 indicates airflow obstruction — the airways are narrowed, and air cannot exit the lungs as quickly as it should
- In obstructive conditions (asthma, COPD), the FEV1 falls disproportionately more than the FVC — so the ratio falls below 0.70
- In restrictive conditions (pulmonary fibrosis), both FEV1 and FVC fall proportionally — so the ratio remains normal or even elevated, despite both absolute values being reduced
Percentage Predicted Values
Raw spirometry numbers in litres are meaningless without context — a FEV1 of 2.5 litres is perfectly normal for a small elderly woman but severely abnormal for a tall young man. Results are therefore compared against predicted values — reference ranges calculated from large population studies of healthy non-smoking adults matched for the same age, height, sex, and ethnic background. Your FEV1 is reported as a percentage of the predicted FEV1 for someone with your characteristics.
Broadly: above 80 percent of predicted is normal; 70 to 79 percent is mildly reduced; 60 to 69 percent is moderately reduced; 50 to 59 percent is moderately severely reduced; and below 50 percent is severely or very severely reduced. These thresholds vary between guidelines, and your pulmonologist will interpret your specific values in the context of your clinical picture rather than applying rigid cutoffs.
What the Patterns of Results Mean
Spirometry results fall into three main patterns, each pointing toward a different category of lung condition.
FEV1/FVC ratio below 0.70, with FEV1 more reduced than FVC. This pattern indicates narrowed airways that obstruct airflow out of the lungs. The most common causes are asthma, COPD, and bronchiectasis. It is the most frequently encountered abnormal pattern in pulmonology practice.
Both FEV1 and FVC reduced proportionally — so the ratio is normal (above 0.70) — but total lung volume is below expected. This indicates lungs that are physically smaller or stiffer than normal, as in pulmonary fibrosis, sarcoidosis, severe obesity, or chest wall deformity. Full confirmation requires measurement of total lung capacity (TLC).
Both obstruction and restriction present simultaneously — FEV1/FVC below 0.70 AND reduced FVC. Seen in advanced COPD with air trapping, combined fibrosis and airway disease, or occupational lung diseases where both mechanisms coexist.
FEV1/FVC above 0.70, both FEV1 and FVC above 80 percent of predicted. A normal spirometry does not rule out all lung conditions — in particular, it does not exclude pulmonary hypertension, early interstitial lung disease, or conditions affecting gas transfer rather than volumes or flows. Additional tests may be needed.
Obstruction on pre-bronchodilator spirometry that improves by 12 percent AND 200 ml after inhaling salbutamol. This reversibility is the defining physiological feature of asthma — distinguishing it from the fixed obstruction of COPD, where bronchodilator response is present but typically smaller and does not fully normalise the ratio.
FEV1/FVC below 0.70 that persists after bronchodilator — obstruction that does not fully reverse. Combined with the patient's smoking history and clinical picture, this pattern confirms COPD. The severity of COPD is graded by the degree of FEV1 reduction: GOLD 1 (mild) above 80%, GOLD 2 (moderate) 50–79%, GOLD 3 (severe) 30–49%, GOLD 4 (very severe) below 30% of predicted.
Spirometry is the only objective measurement we have of airflow limitation. A patient can tell me they feel fine — and their spirometry can show me they have lost 40 percent of their lung function. Conversely, a patient in distress can have entirely normal spirometry — pointing us toward anxiety, cardiac causes, or conditions that spirometry does not capture. The numbers give us a baseline. The clinical story gives them meaning. Together, they guide everything.
— Dr. Nabila Zaheer, Pulmonologist
Beyond Basic Spirometry — Additional Lung Function Tests
While spirometry is the foundation of lung function testing, it measures only airflow and volume. Several additional tests provide information that spirometry alone cannot, and together they form a complete picture of respiratory function.
Lung Volumes — TLC, RV, and FRC
Spirometry cannot measure the air that remains in the lungs after a maximal exhalation — called the residual volume (RV) — because by definition it cannot be blown out. Measuring total lung capacity (TLC), residual volume (RV), and functional residual capacity (FRC) requires additional techniques — body plethysmography (sitting in a sealed chamber) or gas dilution methods. These measurements confirm restrictive patterns, identify air trapping in COPD and asthma, and diagnose hyperinflation — the over-distended lungs characteristic of emphysema.
DLCO — Diffusing Capacity for Carbon Monoxide
DLCO measures how efficiently the lungs transfer gas from the air sacs into the bloodstream — reflecting the health of the alveolar membrane and the pulmonary capillary blood volume. It is abnormal in conditions that damage the alveolar surface: pulmonary fibrosis (reduced DLCO due to thickened alveolar walls), emphysema (reduced DLCO due to destroyed alveolar surface area), and pulmonary hypertension (reduced DLCO due to vascular obliteration). DLCO can be severely reduced in patients whose spirometry is completely normal — which is why a full set of pulmonary function tests, including DLCO, is often needed when spirometry alone does not explain the patient's symptoms.
Flow-Volume Loop
The flow-volume loop is a graphical representation of the spirometry data — plotting airflow rate against the volume exhaled. Its shape provides additional diagnostic information: the characteristic "scooped out" appearance of the expiratory curve in COPD, the variable or fixed upper airway obstruction patterns of tracheal stenosis or vocal cord dysfunction, and the reduced volumes of restrictive disease all produce distinctive flow-volume loop shapes that add to the diagnostic picture.
Peak Flow
Peak expiratory flow (PEF) — measured with an inexpensive handheld peak flow meter — measures the maximum speed of airflow during a forced exhalation. While less precise and reproducible than spirometry, peak flow has an important role in asthma management: twice-daily home peak flow monitoring tracks day-to-day variability in airway function, identifies deterioration before it becomes clinically apparent, and provides objective data for adjusting treatment. Diurnal variability in peak flow — more than 10 percent variation between morning and evening readings — is a hallmark of asthma.
Who Should Have Spirometry?
Spirometry is underused in Pakistan — and as a result, chronic lung diseases are frequently diagnosed late, when significant irreversible damage has already occurred. The following groups should have spirometry performed, in many cases before symptoms become significant enough to demand it.
COPD affects approximately 15 to 20 percent of long-term smokers and causes no symptoms until 40 to 50 percent of lung function has already been lost. A baseline spirometry in every smoker over 40 — repeated annually if normal — provides the earliest possible detection of airflow obstruction, when intervention is most effective. In Pakistan, where smoking rates are high and COPD awareness is low, this simple measure could prevent enormous amounts of preventable disability.
Progressive breathlessness — particularly on exertion — that has not been adequately explained by cardiac evaluation should always include spirometry as a standard investigation. It takes 15 minutes and may reveal the diagnosis that has been elusive. A normal spirometry in a breathless patient is also informative — it reduces the probability of obstructive and restrictive lung disease and directs investigation toward pulmonary vascular disease, cardiac causes, or deconditioning.
A persistent cough or wheeze without a clear infectious cause should always prompt spirometry. Cough-variant asthma and early COPD can present with cough as the sole or primary symptom, with spirometry providing the objective evidence needed for a confident diagnosis and appropriate treatment.
Baseline spirometry before starting employment in a high-risk occupation — stone cutting, textile milling, mining, spray painting — and serial spirometry every one to two years thereafter provides early detection of occupational lung disease when intervention is still meaningful. Post-exposure spirometry for workers leaving high-risk industries is equally important for documenting any existing impairment.
Current international guidelines are clear: a diagnosis of asthma or COPD should be confirmed by spirometry before long-term treatment is started. Clinical diagnosis alone leads to both over-treatment (patients labelled as asthmatic who have a different condition) and under-treatment (patients with COPD not recognised as such). Spirometry-confirmed diagnosis ensures the right treatment for the right condition.
For patients with known asthma, COPD, pulmonary fibrosis, or other chronic lung conditions, serial spirometry provides objective tracking of disease progression and treatment response that symptom assessment alone cannot reliably provide. Annual spirometry in stable COPD patients, and more frequent testing during periods of instability or treatment change, is standard practice.
Before major surgery — particularly thoracic surgery, upper abdominal surgery, or any procedure expected to impact respiratory function — spirometry and full pulmonary function testing quantify pre-operative lung function, identify patients at risk for post-operative pulmonary complications, and guide anaesthetic planning. Patients with significantly reduced FEV1 may require optimisation of their lung condition before surgery can safely proceed.
What Happens If Your Results Are Abnormal?
Receiving abnormal spirometry results is understandably concerning — but it is important to understand what an abnormal result means in context, and what the next steps are.
An abnormal spirometry result is not a diagnosis in itself. It is an objective measurement that tells the doctor the pattern and degree of lung function impairment — obstruction, restriction, or mixed — and its severity. The diagnosis requires this objective measurement to be interpreted alongside the clinical history, symptoms, examination findings, and in many cases additional investigations.
Mildly abnormal results — for example, a FEV1 of 75 percent predicted with a slightly reduced FEV1/FVC ratio — may reflect early disease, normal variation for an individual patient, a suboptimal test effort, or recent respiratory illness temporarily affecting performance. Your pulmonologist will consider all of these possibilities before reaching a diagnosis.
More significantly abnormal results — particularly a FEV1/FVC ratio well below 0.70 with a FEV1 below 60 percent of predicted — indicate meaningful lung function impairment that requires diagnosis, treatment, and follow-up. The appropriate response to such results is not anxiety but action: finding out what is causing the impairment, starting appropriate treatment, addressing any modifiable risk factors such as smoking, and establishing a monitoring plan.
The best spirometry result I can give a patient is a normal one — it is clean, clear reassurance. The second best result I can give them is a clearly abnormal one — because it tells us exactly what we are dealing with and opens the path to treatment. The result I find most difficult is the borderline one, because it demands careful interpretation in context. But even a borderline result is better than no result at all — it is information, and information is always better than uncertainty.
— Dr. Nabila Zaheer, Pulmonologist
Frequently Asked Questions
Does spirometry hurt? Is it safe?
Spirometry is completely painless — there are no needles, no radiation, and no invasive components whatsoever. The forced exhalation manoeuvre requires significant effort and may cause brief dizziness or lightheadedness in some patients, particularly those with severe lung disease. This resolves immediately with rest. Spirometry is very rarely contraindicated — it should be deferred in patients with very recent eye surgery, active haemoptysis (coughing blood), or acute cardiovascular events, and performed with caution in those with very severe lung disease or active respiratory infections. For the vast majority of patients, it is completely safe and very well tolerated.
My spirometry was normal but I am still breathless. Does that mean the problem is in my head?
Absolutely not. Normal spirometry does not mean your breathlessness is imagined or psychological. It means that obstructive and restrictive patterns of lung function impairment are not the primary explanation for your symptoms. Several serious conditions cause significant breathlessness with completely normal spirometry: pulmonary hypertension, cardiac disease, pulmonary embolism, early pulmonary fibrosis (which may be missed on spirometry but detected on DLCO), anaemia, and breathing pattern disorder. A normal spirometry in a breathless patient should redirect investigation — not close it. Tell your doctor explicitly that you want further investigation of your breathlessness despite the normal spirometry result.
I have been told I have asthma, but I have never had spirometry. Should I be concerned?
Yes — this is a clinically important issue. International guidelines for asthma management are clear that a diagnosis of asthma should be confirmed by objective lung function testing — specifically spirometry with bronchodilator reversibility — before long-term treatment is started. Studies show that between 30 and 40 percent of patients diagnosed with asthma on clinical grounds alone do not have asthma when objectively tested. Some of these patients have a different condition requiring different treatment. Others have been over-treated for years with medications they did not need. If you have been labelled as asthmatic without spirometry, please ask your pulmonologist for objective confirmation of the diagnosis.
Can spirometry results change over time?
Yes — and tracking that change over time is one of spirometry's most valuable uses. In healthy non-smoking adults, lung function peaks in the mid-twenties and then declines gradually at approximately 20 to 30 ml per year. In smokers with COPD, the rate of decline is approximately twice as fast — around 50 to 60 ml per year. In patients with asthma on appropriate treatment, lung function should remain stable or improve. Serial spirometry — comparing results from year to year — therefore provides objective evidence of disease progression, treatment effectiveness, and the impact of interventions such as smoking cessation. A single spirometry measurement is a snapshot; serial measurements tell the story.
Where can I get spirometry done in Rawalpindi or Islamabad?
Spirometry is available at pulmonology clinics, respiratory medicine departments of major hospitals, and some well-equipped general practice and diagnostic facilities across Rawalpindi and Islamabad. At PulmoCare, spirometry with bronchodilator reversibility testing is performed by trained technicians using calibrated equipment, and results are interpreted by Dr. Nabila Zaheer in the context of a full clinical assessment. The test is quick, affordable, and can be arranged at the time of your consultation. If you have been referred for spirometry or want a baseline assessment of your lung health, please book an appointment directly.
Know Your Numbers. Understand Your Lungs.
Spirometry takes 15 minutes and can reveal lung conditions that have been silently developing for years. Whether you need your first baseline assessment, want to understand results you have already received, or need serial monitoring of a known condition — Dr. Nabila Zaheer at PulmoCare provides expert spirometry and full pulmonary function testing with clear, personalised explanation of every result.
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