Asthma can feel unpredictable, but your lung tests give clear answers about how well it’s controlled. Pulmonary function tests measure how much air you can move in and out of your lungs and how quickly it happens.
These results show whether your current treatment keeps your airways open or if adjustments are needed to improve control. When you blow into a spirometer or complete other breathing tests, the numbers reveal more than just lung strength.
They uncover patterns that point to airway narrowing, inflammation, or triggers that may be affecting your breathing. By tracking these results over time, you can determine whether your asthma is stable, improving, or worsening.
Your test results don’t just sit on a chart—they guide your care plan. They help your doctor decide if your medication needs to change, whether your lungs respond well to treatment, and how to prevent flare-ups before they start.
Pulmonary function tests give you measurable information about how well your lungs move air in and out. These results help your doctor diagnose asthma, track changes in your breathing, and determine if your treatment is effective.
Pulmonary function tests (PFTs) are non-invasive exams that measure how well your lungs work. They check the amount of air you can inhale and exhale, as well as how quickly you can move air through your airways.
These tests are critical when you experience symptoms such as wheezing, coughing, or shortness of breath. They can also show how much asthma affects your breathing over time.
PFTs are often used in conjunction with your medical history and physical examination. This combination helps your healthcare provider determine whether your breathing issues are caused by asthma or another respiratory condition.
Several types of pulmonary function tests can be used to evaluate asthma. Each test gives different information about your lung function.
Common tests include:
Spirometry is the most common test for asthma. It can detect airflow obstruction and show improvement after inhaled medication, which supports a diagnosis of asthma.
Other tests are used if the results are unclear or if your doctor needs more detailed information about your lung function.
Asthma diagnosis requires more than symptoms alone. Pulmonary function tests provide the objective evidence needed to confirm the condition.
With spirometry, doctors look for variable airflow obstruction, meaning your airways narrow and then improve after using a bronchodilator. This pattern is a key feature of asthma.
If spirometry is normal but asthma is still suspected, a methacholine challenge may be ordered. This test checks if your airways are unusually reactive, a condition commonly associated with asthma.
By combining test results with your history of symptoms, your healthcare provider can determine if you have asthma, its severity, and whether your current treatment is effectively controlling your lung function.
Pulmonary function testing uses specific measurements to show how well your lungs move air and exchange gases. These values help determine whether your breathing problems are caused by airway obstruction, restricted lung expansion, or a combination of both.
Forced Vital Capacity (FVC) measures the total amount of air you can exhale after taking the deepest breath possible. It reflects your lungs’ ability to fill and empty with each breath.
A reduced FVC often points to restrictive lung disease, such as pulmonary fibrosis, or conditions that limit chest expansion. In these cases, your lungs cannot hold as much air, leading to lower lung volumes.
Your FVC result is compared to predicted values based on your age, height, sex, and ethnicity. A value below 80% of the predicted is usually considered abnormal.
Monitoring FVC over time helps track whether your lung function is stable, improving, or declining. This makes it an essential tool for following asthma control and other chronic lung conditions.
FEV1 measures how much air you can forcefully blow out in the first second of your exhalation. It is one of the most important markers of airflow limitation.
In asthma, a low FEV1 typically indicates that your airways are narrowed or inflamed. The lower the FEV1, the more severe the obstruction.
Your doctor often looks at FEV1 as a percentage of predicted values. For example:
Tracking your FEV1 regularly can help determine how well your asthma treatment is working and whether any adjustments are needed.
FEV1/FVC Ratio and Its Importance
The FEV1/FVC ratio compares the amount of air you exhale in the first second (FEV1) to your total forced exhalation (FVC). This ratio helps distinguish between obstructive and restrictive patterns of breathing.
For asthma, a low FEV1/FVC ratio signals airway obstruction. If the ratio improves after using a bronchodilator, this suggests reversible obstruction, which is typical of asthma.
This measurement is especially valuable because it highlights airway narrowing even when other values look close to normal.
Lung volume testing extends beyond FVC and FEV1 by measuring the amount of air your lungs can hold during different phases of breathing.
Key terms include:
In asthma, RV often increases because trapped air remains in your lungs after exhalation. This can cause your chest to feel tight and reduce your breathing efficiency.
A low TLC points to restrictive problems, while a high TLC with increased RV is more common in obstructive diseases. These measurements give a clearer picture of how your lungs are functioning beyond basic airflow tests.
Pulmonary function tests give objective measurements of how well your lungs are working. They help you and your doctor see whether airflow is limited, whether the limitation changes with treatment, and how these results compare to reference standards.
When reviewing your pulmonary function test (PFT), the first step is to compare your results to predicted normal values. These values are based on age, height, sex, and ethnicity.
Many labs now use z-scores recommended by the ERS/ATS to show how far your results deviate from the expected range. In asthma, a key measurement is the FEV1/FVC ratio.
A reduced ratio often signals obstructive lung disease. If your ratio is below the lower limit of normal, airway narrowing is likely present.
Other values, such as FEV1 percent predicted, help classify the severity of obstruction. For example:
| Severity (based on FEV1 % predicted) | Interpretation |
| ≥80% | Normal or mild |
| 60–79% | Moderate |
| 40–59% | Moderately severe |
| <40% | Severe |
Seeing normal values does not rule out asthma, but abnormal values make airflow limitation more evident.
Specific spirometry interpretation patterns suggest that your asthma may not be well-controlled. A low FEV1 compared to predicted values is one of the strongest markers.
If your FEV1 is consistently reduced, it may mean ongoing inflammation or airway remodeling. A low peak expiratory flow (PEF) can also point to poor control.
Daily changes in PEF greater than 20% are often considered significant. This variability shows unstable airway function.
You may also notice a high residual volume (RV) or total lung capacity (TLC). These can indicate air trapping and hyperinflation, which are common in uncontrolled asthma.
Doctors sometimes reference GOLD criteria, usually applied in COPD, to compare obstructive patterns. While asthma is distinct, overlap in interpretation can highlight persistent obstruction that needs closer management.
A significant part of PFT interpretation in asthma is testing reversibility. This involves repeating spirometry after using a bronchodilator.
If your FEV1 increases by at least 12% and 200 mL, this is considered a significant response. This improvement indicates that airway narrowing is reversible, which supports a diagnosis of asthma.
A strong bronchodilator response also suggests that your symptoms may improve with proper treatment. If the change is minimal, it may indicate that your asthma is not well-controlled or that another condition is contributing.
In some cases, further testing, such as a methacholine challenge, is used to assess airway hyperresponsiveness. Tracking reversibility over time helps you and your healthcare provider determine whether therapy is maintaining your airways’ flexibility or if adjustments are needed.
Advanced testing can provide more precise information about how your lungs function and how well your asthma is being controlled. These tests extend beyond basic spirometry and can reveal underlying issues, such as reduced gas exchange, airway inflammation, or abnormal responses to treatment.
A diffusing capacity test (DLCO) measures how well gases like oxygen move from your lungs into your blood. In this test, you inhale a small amount of carbon monoxide, which is safe at low levels, and the machine measures the amount absorbed.
This shows how efficiently your lungs transfer gases. Your alveolar volume (VA) is also measured during the test.
It represents the total volume of air in your alveoli, the tiny sacs where gas exchange happens. When combined with DLCO, the DLCO/VA ratio helps determine if reduced gas exchange is due to lung tissue problems or changes in lung volume.
For asthma, the DLCO is usually normal; however, changes may occur if you also have other conditions, such as emphysema or pulmonary vascular disease. Hyperinflation, which can occur in poorly controlled asthma, may affect alveolar volume and alter your results.
This test helps your doctor distinguish between asthma-related symptoms and other potential lung issues, ensuring that your treatment plan is based on accurate findings.
Fractional exhaled nitric oxide (FeNO) testing measures the level of nitric oxide in your breath. Nitric oxide is a marker of airway inflammation, especially in allergic or eosinophilic asthma.
At Gwinnett Pulmonary, this test is done by having you exhale steadily into a specialized device. The results are reported in parts per billion (ppb).
Because results are available immediately, your provider can adjust medications during the same visit. If your FeNO level is high, it may indicate that you require additional anti-inflammatory treatment, such as inhaled corticosteroids.
If it is consistently low, your doctor may consider lowering your dose. This test is quick, non-invasive, and provides objective data that supports treatment decisions.
Asthma is closely tied to airway inflammation, and identifying its level is key to controlling symptoms. Traditional lung function tests measure airflow but may not accurately reflect the degree of inflammation in your airways.
That is where markers like FeNO and DLCO/VA become valuable. Inflammation can vary over time, even when your breathing tests look normal.
By tracking inflammation markers, your doctor can detect early signs of worsening asthma before you experience any noticeable symptoms. Regular monitoring also helps confirm whether you are taking your medications correctly.
For example, if your FeNO level remains high despite treatment, it may suggest missed doses or the need for more intensive therapy.
Your pulmonary test results do not exist in isolation. Measurable traits shape them, the way your symptoms behave over time, and other health conditions that may impact your breathing.
Understanding these factors helps you see why results can vary and why your doctor may repeat or compare tests across visits.
Your age and height directly affect normal lung values. Taller individuals usually have larger lungs, which means they have higher expected volumes.
As you age, lung elasticity decreases, and test values like Forced Vital Capacity (FVC) and Forced Expiratory Volume in 1 second (FEV1) often decline. Predicted values are based on extensive population studies.
These reference ranges also take into account sex and ethnicity, as lung size and function vary across these groups. For example, a normal FEV1 for a 25-year-old male who is 6 feet tall will differ from that of a 65-year-old female who is 5 feet tall.
Your doctor compares your results against these predicted values to decide if your airflow is within a normal range. This is why two people with the same measured FEV1 can have very different interpretations depending on their baseline characteristics.
Asthma is often unpredictable. Your results may look normal on one day and abnormal on another, depending on whether you are experiencing wheezing, shortness of breath, or chest tightness.
Pulmonary tests capture your lung function at the time of testing, not across all situations. Common triggers—such as allergens, exercise, respiratory infections, or smoke—can temporarily worsen airway narrowing
If you had exposure shortly before your test, your results may show more obstruction than usual. Doctors sometimes use a bronchodilator challenge to see if your numbers improve after medication.
This helps confirm whether reversible airway narrowing is a factor in your asthma control. Because symptoms and triggers vary, your allergist or pulmonologist may schedule repeat tests to track changes over time.
Other health conditions can affect the appearance of your pulmonary test. For example, COPD can lower FEV1 and the FEV1/FVC ratio, making it harder to separate from asthma.
Interstitial lung disease often reduces lung volumes and diffusing capacity, which may mimic restrictive patterns. Non-respiratory conditions also play a role.
Obesity can limit chest expansion, while gastroesophageal reflux disease (GERD) may worsen asthma symptoms and cause cough or dyspnea. Allergies and sinus disease can add nasal congestion, which affects breathing patterns during testing.
Because these conditions overlap, your doctor may order additional exams or review your medical history closely. This ensures that your pulmonary test reflects not only your asthma but also any other issues that may influence your breathing results.
Pulmonary test results give you measurable data about your lung function, airway inflammation, and response to treatment. Using these results helps you and your healthcare team make informed choices about medication, lifestyle changes, and long-term asthma control.
Your test results help your doctor or allergist tailor a treatment plan that matches your specific type of asthma. For example, spirometry may show reduced airflow, while FeNO testing can reveal airway inflammation.
These findings guide whether you need inhaled corticosteroids, long-acting bronchodilators, or other medications. Asthma is not the same for everyone.
Some people respond well to low-dose inhalers, while others need combination therapy. By reviewing your test data, your provider can determine the safest and most effective dose.
Personalized planning also includes identifying triggers. If your results indicate increased inflammation after allergen exposure, your healthcare provider may recommend allergy testing or adjustments to your environment.
Your lung function and inflammation levels can change over time, and pulmonary tests help track these changes. Regular spirometry or FeNO testing can help determine if your current therapy is effective or if adjustments are necessary.
If your test results indicate worsening obstruction or rising inflammation, your healthcare provider may increase the strength of your medication or add another therapy. On the other hand, stable results allow for lower doses to be administered, thereby reducing the likelihood of side effects.
Tracking your results over months creates a clearer picture of your asthma pattern. This approach helps avoid unnecessary medication changes and ensures that adjustments are based on objective data, not just symptoms.
Understanding your test results plays a significant role in managing asthma. When you know what the numbers mean, you can see how your daily habits and medication use affect your lung health.
Your provider may use charts or score sheets, such as the Asthma Control Test, to explain your progress. Clear communication helps you recognize early signs of poor control and take action before symptoms worsen.
Support also includes teaching you how to use inhalers correctly. You can also learn how to follow an asthma action plan and identify and avoid triggers.
Pulmonary tests offer a window into how well your asthma is managed. By measuring airflow, lung capacity, and airway inflammation, these tests reveal whether your treatment keeps symptoms under control or changes are needed. Tracking these results over time helps identify patterns, confirm improvements, and prevent flare-ups before they escalate. For patients, understanding these results builds confidence and empowers better daily management. For providers, it ensures that treatment remains personalized and effective. These insights make pulmonary testing an essential part of long-term asthma care.
If you want clarity on your asthma control and expert guidance on your results, book an appointment with Gwinnett Pulmonary & Sleep today and take the next step toward easier breathing.
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