Reading a Spirometry Report — One Point Among Your Peers, Two Graphs Drawn by a Breath

When You Get Your Results Sheet

Many people have put a tube in their mouth in a testing room, taken a deep breath in, and then breathed out to the sound of "More, more, all the way out!" It often doesn't end with just one try, and you may hear "One more time" several times. A few days later, the paper you receive has a few lines of numbers with English abbreviations, a column with percentages next to them, and two graphs.

A pulmonary function test measures the volume and speed of the air you exhale by having you take a deep breath in and then blow it out as hard as you can. On the results sheet, that volume and speed appear both as numbers and as graphs tracing the shape of the outgoing breath (PMID 34752275).

This article walks through how to read those numbers and graphs. We will cover what the numbers are compared against, who draws the line of "normal" and where, and what the shapes of the graphs let us guess versus what they cannot tell us. While centered on international interpretation standards, this is written alongside test guidelines published in Korean academic journals and domestic research for readers holding a results sheet received in Korea. The individual diseases where breathing breaks down are handled in the later parts of this series.

With All Your Might, to the Very End, and Again and Again

What the test measures is the air escaping your airways. Airways are the system of tubes through which air travels from the nose and mouth deep into the lungs. You take in as deep a breath as you can to fill your lungs, and then, on cue, you exhale with all your might, all the way to the end. The first three numbers to read among the lines on the result sheet come from that.

FEV1 is the volume of air that leaves in the first second when you exhale as hard as you can after taking in as deep a breath as possible. When airways are wide, a large volume of air rushes out right from the start.

FVC is the total volume of air that leaves when you exhale as hard as you can to the very end in the same way. FEV1 and FVC are written in liters.

The FEV1/FVC ratio is the fraction of the total volume exhaled to the end that left in the first second. On the result sheet, it is written as a decimal between 0 and 1, or as a percentage.

These numbers depend on the effort made by the person taking the test. That is why the test has established standards. The American Thoracic Society (ATS) and the European Respiratory Society (ERS) jointly updated the technical standards for this test in 2019, seeking to make measurements more precise and consistent (PMID 31613151). When evaluating the quality of a breath, two things are looked at: whether a single blown breath is acceptable, and whether breaths blown multiple times are consistent with one another. A South African guideline for workplace spirometry specifies that the test should continue until there are at least three acceptable curves and two of them match closely (PMID 23237126), and some guidelines state to repeat the test up to eight times until that standard is met (PMID 28416951). This is why you hear "one more time" in the testing room several times.

Breaths that fail to meet the standard make the numbers hard to trust. There are reports that the proportion of acceptable tests in primary care is low, which can lower the validity of the results and affect clinical judgment (PMID 18166597). A testing guideline published in the 2017 Journal of the Korean Academy of Tuberculosis and Respiratory Diseases also notes that the quality of the test must be secured before reading the results (PMID 28416951).

When an obstruction is seen, the test particularly proceeds to an extra step. Bronchi are tubes where the airways descending from the throat branch into both lungs and grow progressively narrower. You inhale a medication that widens those bronchi and then blow again.

A bronchodilator is a medicine that relaxes the muscles surrounding the bronchi to widen narrowed airways. The method of comparing the numbers before and after using the medication will be looked at separately later (PMID 28416951).

Because the numbers on the result sheet are values derived from a breath blown with all your might, to the very end, and multiple times, whether that breath met the standard comes first.

Where Do You Stand Among Your Peers?

The same value of 2.5 liters cannot mean the same thing to a 20-year-old young man who is 180 centimeters tall and an 80-year-old grandmother who is 150 centimeters tall, because lung function values vary depending on height, sex, and age (PMID 40769600). That is why the report sheet lists the comparison value right next to the measured value.

The predicted value is the value expected from a healthy person of the same age, height, and sex. The column on the report sheet with percentages is usually the measured value divided by this predicted value. In the percentage rows, it is easy to confuse these two. The value where the ratio itself is written as a percentage (the fraction that came out in the first second) and the percentage comparing that ratio back to the predicted value are different numbers. Predicted values come from reference equations. Reference equations are calculation formulas created by gathering many healthy people, measuring them, and figuring out how values change depending on age, height, and sex.

Reading this is similar to placing a child's height on a growth chart. The reference equation for lung function can be read like a pediatric growth chart, and it includes height, sex, and age (PMID 40769600). The fact that a child's height is 120 centimeters does not allow us to say whether they are tall or short; we must look at where they stand among children of the same age and sex. Lung function numbers are also read by where they stand among healthy people of the same age, height, and sex.

Just as a growth chart has a bottom line, lung function has a lower boundary. The lower limit of normal is the line that separates the bottom 5% among healthy people of the same age, height, and sex.

Some results write that position as a single number. The z-score is a number measuring how far a measured value falls above or below the average of healthy people, using the spread of those people as a yardstick. If it is 0, it is the average, and the larger the negative number, the closer it is to the bottom end.

There are broadly two ways to draw the line of normal. One is a fixed value that is the same for everyone. 80% of the predicted value is such a line, and many studies have used it in their definitions (PMID 34905031, PMID 41891755). The FEV1/FVC ratio of 0.7 is also such a line. The other is the lower limit of normal and the z-score. The 2022 European Respiratory Society and American Thoracic Society interpretation standards addressed the method of screening out unusually low or high results based on the normal range of healthy people (PMID 34949706), and a review summarizing this standard picks out using z-scores instead of percentages of the predicted value as one of the changed points. The same review evaluates this standard as a major step forward, yet notes that challenges still remain in introducing aspects such as severity classification into actual clinical practice (PMID 40084848). One review views that interpretation has shifted toward gauging the probability of disease rather than a definitive diagnosis (PMID 38999220). The Thoracic Society of Australia and New Zealand also recommended in 2016 to read by the lower limit of normal, and if possible, by z-scores (PMID 27457870).

Not all guidelines have shifted in this direction. The Global Initiative for Chronic Obstructive Lung Disease (GOLD) notes that for a person with longstanding respiratory symptoms or exposure to risk factors, chronic obstructive pulmonary disease should be suspected, and to firmly establish that diagnosis, the FEV1/FVC ratio after using a bronchodilator must be below 0.7 (PMID 39638416). This 2017 domestic guideline chose to use a fixed reference value instead of the lower limit of normal, citing convenience as the reason (PMID 28416951). This means that depending on which guideline is used to read the same report sheet, the line of "normal" can be drawn in a different place. For quite a few people, the interpretation column also changes depending on whose reference equations made from which healthy people's data are used (PMID 37523681, PMID 42556745).

The growth chart analogy has limitations. Because the lower limit of normal is a line drawn so that 1 in 20 healthy people will fall below it, being outside the line does not immediately mean disease. Nor does being inside the line mean health. The same concern arises on the side of fixed criteria. A review notes that fixed criteria like 0.7 can miss early stages of disease, so symptoms, various tests, and imaging must be looked at together (PMID 39189795).

The numbers on a report sheet are not high or low in themselves, but are read by where they stand among healthy people of the same age, height, and sex. Where the line of normal is drawn differs by guideline.

The Line at 0.7

Even for the same group of people, where you draw the line changes the number of people who are read as obstructed. Among 4,882 Canadian residents aged 40 and older, the proportion read as having blocked airways who could not push air out well was 17% when split by a fixed ratio of 0.7, and 11% when split by the lower limit of normal (PMID 25583891).

That difference widens as people get older. The FEV1/FVC ratio gradually decreases from childhood into older age even in healthy people (PMID 41912392). Yet if we apply the same 0.7 to everyone, older people are read as abnormal more often, and younger people less often. Among local residents, the proportion of those 65 and older read as obstructed was 14.9% by the lower limit of normal and 31.1% by the fixed ratio (PMID 19654942). A study re-reading 27,307 test records of adult men using a North Indian reference equation concluded that while the two methods mostly agreed overall, they diverged as age increased, and the fixed ratio overdiagnosed obstruction in middle-aged and older men while underdiagnosing it in younger men (PMID 21605485). In the earlier Canadian residents, the degree to which people caught only by the fixed ratio was associated with bad outcomes like self-reported symptoms and disability was generally small and not statistically meaningful. The authors suggested that using only a fixed ratio can lead to misdiagnosis, proposing that to reduce overdiagnosis we should diagnose only when a low ratio and a low FEV1 are present together (PMID 25583891).

The people missed on the younger end may not be trivial either. In a study following 95,288 Copenhagen residents in Denmark, 1% had a ratio of 0.7 or higher—so they were normal by the fixed ratio—yet fell below the lower limit of normal. These individuals had a higher risk of pneumonia, heart failure, and death than people without obstruction (PMID 29449425). This is an observational study following the residents of a city.

The situation is similar on the other side. Among 3,802 Spaniards aged 40 to 80, people whose ratio was below 0.7 but above the lower limit of normal had worse self-rated quality of life than those without obstruction. There was no difference in exercise capacity, number of exacerbations, or cardiovascular disease risk (PMID 21183609). The fixed ratio has the advantage of being easy to use, and it is still the line used by GOLD (PMID 28416951, PMID 39638416).

Because test values have inherent biological variation (PMID 34949706), results right near the line can fluctuate. GOLD recommends retesting to confirm the diagnosis if the result after using a bronchodilator comes out close to the cutoff (PMID 39638416).

The fixed ratio tends to read abnormalities more often in older people and less often in younger people, and guidelines still differ on which line to use.

Two Graphs Drawn by the Breath

The two graphs on the report are drawings of that exact breath from which the three numbers came.

The volume-time graph is a graph that draws how the amount of exhaled air piles up over time, starting from when the exhalation began. The horizontal axis is time, and the vertical axis is the exhaled amount. The curve rises steeply at first, gradually flattens out, and finally becomes flat. The height read at the 1-second mark is FEV1, and the height where it stops rising and flattens out is FVC.

The flow-volume loop is a loop that draws the speed of air while exhaling, matched against the amount exhaled up to that point, and continues on to even the inhaled breath. It is a graph obtained while taking a breath in as fully as possible and then exhaling (PMID 35130676). The exhalation side shoots up to its fastest peak right as it begins, and then slopes down as the lungs empty out. The inhalation side continues beneath it like a round semicircle.

There is a review article stating that one should not skip the graphs and just look at the numbers. It advises reading the two graphs together with the numbers representing the volume and speed of the breath (PMID 35130676).

On the volume-time graph, one reads the height at 1 second and the height at the end; on the flow-volume loop, one reads the shape of how fast the breath escapes.

Reading Patterns by Shape

After comparing against healthy individuals, the next task is to determine the shape of the abnormality: whether it is an obstructed shape, a reduced shape, or normal (PMID 39644209, PMID 14621232).

An obstructive pattern is a shape where the FEV1/FVC ratio is low, meaning that of the breath exhaled all the way, the fraction that went out in the first second is small. When airways are narrow, less air rushes out right from the start. On the flow-volume loop, a shape where the expiratory limb caves inward is noted as a feature of chronic obstructive pulmonary disease (PMID 31511572). Such an obstructed shape is seen, for example, in asthma or chronic obstructive pulmonary disease, and the two diseases are covered by "What Is Asthma? — An Airway That Too Easily Tightens, and the Inflammation That Keeps It Swollen" and "What Is COPD? — A Balloon That Won't Empty, and the Breath That Leaves in the First Second."

A restrictive pattern is a shape where the FVC is low while the FEV1/FVC ratio is normal or even high. Because the airways are not blocked, this is a shape where the total amount of breath that can be exhaled is small, which is used to indirectly gauge whether the lungs have become small or fail to expand fully when lung volumes are not measured (PMID 36870424). This shape is also seen in diseases where scars accumulate on the walls between air sacs inside the lungs, causing the lungs to stiffen (covered by "What Is Pulmonary Fibrosis? — Thickening Paper Windows, Scars on the Wall Oxygen Crosses"), and it commonly appears alongside obesity. In a study examining 300 adults who showed this shape, half were obese, and obesity was associated with all shapes (PMID 27812633).

However, this test alone cannot confirm whether the lungs have truly become small. Total lung capacity is the total amount of air contained inside the lungs when taking in as deep a breath as possible. Because air remains inside the lungs even after exhaling all the way, this value cannot be known through a test where one breathes out into a device. Lung volume tests, performed by placing the person inside a sealed box or having them breathe in a mixed gas, are used separately (PMID 40769589), and lung volumes must be measured directly in this way to confirm small lungs (PMID 36870424). Depending on the hospital, pulmonary function test report sheets may also include lines measuring lung volumes or the capacity for oxygen to cross from the lungs into the blood. The pulmonary function test referred to in this article is the test in which one blows out air (PMID 34752275).

Among people who appear to have a restriction, the number of people whose lungs are actually small may be small. In data from 8,891 general residents (aged 6 to 82) collected by an institution in Vienna, Austria, people with genuinely small lungs were rare at 1.1%, and among those who showed this shape on pulmonary function tests, actual small lungs were confirmed by lung volume testing in 18.0%. Conversely, among those who did not show this shape on pulmonary function tests, 99.6% did not actually have small lungs either (PMID 36870424). The 300 adults mentioned earlier were patients who received clinical care; when even their lung volumes were measured, 36% actually had reduced lung sizes, 40% had obstruction or a mix of obstruction and reduced size, and 24% had normal lung sizes with no obstruction. The authors concluded that obstruction is common in such people and that measuring lung volumes is frequently necessary (PMID 27812633).

A mixed pattern is a shape where airway obstruction and reduced lungs are present together in one person. The earlier study grouped cases where lung volumes were reduced and traces of obstruction were also present in this way (PMID 27812633). How to classify mixed patterns and grade their severity remains an unclear point even after the 2022 standards (PMID 39644209).

There is one more place where the shape of the loop is particularly useful: when the large airways in the neck or upper chest become narrowed. There is a review stating that the shape of the flow-volume loop helps detect such upper airway obstruction and surmise its location (PMID 35130676). In such cases, the peak on the expiratory side may appear flattened like a plateau. However, in a study examining 59 patients at one hospital, this shape was also seen in people whose large airways were not obstructed, and the obstruction was strongly suggested only when numbers such as the fastest expiratory speed were also significantly lowered together (PMID 40786950). In a study examining 475 loops at another hospital, the visual criterion of looking at the loops had low performance in screening out such obstruction, and confirmation of the obstruction was done via bronchoscopy or laryngoscopy to look directly inside the airways, or CT scans of the neck and chest (PMID 19327182).

Shapes tell us what to suspect, but small lungs are confirmed with lung volume tests, and the causes are sorted out alongside other information.

Breathing In Medicine and Blowing Again

The test of breathing in medicine and blowing again is used especially when an obstruction is seen. A bronchodilator response is how much the FEV1 or FVC measured before and after inhaling a bronchodilator changes. It looks at how much the narrowed airway widens back up with medicine, and is used to diagnose and evaluate asthma and chronic obstructive pulmonary disease when an obstruction is seen (PMID 28416951). The shape of the flow-volume loop also helps find out the response to medicine (PMID 35130676).

Guidelines decide how much of a change means there is a response. The domestic guideline from 2017 mentioned earlier recorded an increase in FEV1 or FVC of 12% or more from the initial value, and by an amount of 200mL or more, as the commonly used definition of a positive response (PMID 28416951). The 2022 European Respiratory Society and American Thoracic Society standards newly set the criteria for this response (PMID 40084848). Even with the same result, the judgment can change depending on which year's and which guideline's rules are used to read it.

The values before and after using medicine also have different uses. GOLD 2025 recommends excluding chronic obstructive pulmonary disease using the pre-medication value, and confirming the diagnosis using the post-medication value. The same document notes that people whose ratio was below 0.7 before medicine but rose to 0.7 or higher after medicine have a greater chance of developing an obstruction that remains even later after medicine, so they must be watched over time (PMID 39638416). This means the story does not end just because they fall into the normal box after using medicine.

A bronchodilator response looks at how much the airway widens back up with medicine, its criteria for judgment are set by guidelines, and they have changed over time.

The Gray Area — When the Ratio Is Normal but FEV1 Is Low

Some items on the report do not fit neatly into any single box. This is when the share that leaves in the first second is normal, but FEV1 itself is low. PRISm is a state where the FEV1/FVC ratio is normal, but FEV1 is low. The name comes from taking the first letters of an English phrase meaning that the ratio was preserved while lung function dropped.

It is not rare. In a meta-analysis combining general population studies from 31 countries, PRISm measured by the GOLD definition was 10.60% (PMID 41891755), and other meta-analyses counted it at roughly 10 to 12% (PMID 41777125, PMID 39742912). That is roughly 1 in every 10 people. However, this number varies greatly depending on the definition. For the exact same people, the figures swung from 2.0% to 12.5% depending on which reference equation and cutoff line were used (PMID 40453983), and even the names and definitions used to call this state vary from study to study (PMID 41813011).

PRISm has been linked to mortality risk in observational studies. In a study pooling 9 general population cohorts in the United States, deaths adjusted for age and smoking when following 1,000 people for 1 year were 18.0 people with normal lung function and 29.6 people with PRISm. The authors noted this as a small but statistically meaningful increase in risk, and added that further research is needed to determine whether this link is one of cause and effect (PMID 34905031). Meta-analyses pooling multiple cohorts also reported increased risks of all-cause mortality and cardiovascular mortality (PMID 37914194, PMID 38971833). In data from about 350,000 people in the UK, PRISm was also linked to an increased risk of death, and the authors noted that it did not seem explained by smoking, obesity, or pre-existing lung disease. However, the same authors added that for many people, PRISm is temporary (PMID 34739861).

That was not the case in every group. In a study following a regional middle-aged cohort in Korea for an average of 16.5 years, all-cause and cardiovascular mortality in people with PRISm did not increase with statistical clarity compared to people with normal results. The authors wrote that further research is needed to screen out low-risk groups (PMID 37138264).

Over time, paths diverge. In meta-analyses, among people with PRISm, 10 to 50% returned to normal, 20 to 60% remained the same, and 6 to 53% progressed to What Is COPD? — A Balloon That Won't Empty, and the Breath That Leaves in the First Second (PMID 41777125). The ranges vary widely across studies. There is also no consensus yet on what to do about this state. GOLD introduced PRISm as one of the concepts to find people at risk of developing obstruction, but a definition widely accepted by the medical community does not yet exist, and therefore the foundation to test how to manage it has not yet been established (PMID 37629335).

PRISm is common and has been linked to death and cardiovascular disease in observational studies, but whether it is a cause is not established, and over time, some people return to normal, some stay the same, and some progress to What Is COPD? — A Balloon That Won't Empty, and the Breath That Leaves in the First Second.

Two Test Reports

Let us compare what we saw earlier to two test report sheets. A seventy-year-old father and a thirty-year-old daughter were tested on the same day, and both had an FEV1/FVC ratio around 0.7.

The father's ratio is slightly lower than 0.7, but it sits above the lower limit of normal for healthy people of the same age, height, and sex. Read by the fixed ratio, it falls in the obstruction box; read by the lower limit of normal, it falls in the normal box. Because the ratio declines with age even in healthy people (PMID 41912392), such a split between the two lines happens more often in older adults (PMID 19654942, PMID 21605485). People with a split like this rated their own quality of life worse than those without obstruction, while showing no difference in exercise capacity, exacerbations, or cardiovascular disease risk (PMID 21183609).

The daughter's ratio is higher than 0.7, but lower than the lower limit of normal for a thirty-year-old. By the fixed ratio, it is in the normal box; by the lower limit of normal, it is in the obstruction box. Young and middle-aged adults who fall outside the fixed ratio in this way showed a higher risk of pneumonia, heart failure, and death in a city resident study (PMID 29449425).

Both results sit right near the line. If these values were obtained after using a bronchodilator, a physician following GOLD would recheck them to confirm (PMID 39638416). And either way, what these numbers mean is not determined by the test report alone. They are read together with whether symptoms like shortness of breath or a cough are present, whether the person smoked, and what physical examination and other tests show (PMID 14621232).

The exact same ratio can fall into different boxes depending on age, and whichever box it lands in, its meaning is determined together by symptoms and medical history.

What the Report Sheet Cannot Tell You

Pulmonary function tests show patterns like blockages or smaller lungs, but they cannot separate the causes on their own. Therefore, they are read in light of medical history, physical exams, and other tests (PMID 14621232). The 2022 European Respiratory Society and American Thoracic Society interpretation standards note in their conclusion that reading the results must be accompanied by clinical expertise, and must account for the biological variation of the test itself and the uncertainty of the results (PMID 34949706). The study that created the new 2022 international reference equations also notes that when reading results with those equations, that person's symptoms and medical history must be carefully considered (PMID 36383197).

A "normal" judgment is also not the end. If shortness of breath or coughing persists but the numbers fall in the normal column, do not stop there—other tests may be needed. A review states that fixed thresholds like 0.7 alone can miss early stages of disease, making an approach that combines symptom evaluation, various physiological tests, and imaging necessary (PMID 39189795). There are also results like PRISm, seen earlier, that do not fit neatly into any single column.

That does not mean the usefulness of this test is small. Pulmonary function tests are a valuable tool used to evaluate people with respiratory symptoms in primary care, to diagnose or rule out chronic obstructive pulmonary disease, sometimes to confirm asthma, and to see if treatments are working (PMID 18166597). Which column the numbers on the report sheet fall into, and what to look at next, are decided by a doctor who knows that person's symptoms and medical history.

Pulmonary function tests show the pattern of breathing but cannot separate the causes, and their results are read by a doctor together with symptoms, medical history, and other tests.

Where to Look Next

What the airway looks like and where air meets blood is followed by "How Do We Breathe? — An Upside-Down Tree, and the Leaves Where Air Meets Blood" right before this article. Diseases where a blocked shape is visible are covered by "What Is Asthma? — An Airway That Tightens Too Easily, and the Inflammation That Keeps It Swollen" and "What Is COPD? — A Balloon That Won't Empty, and the Breath That Leaves in the First Second", while one of the diseases where a shape suggesting a shrunken lung is suspected is covered by "What Is Pulmonary Fibrosis? — Thickening Paper Windows, Scars on the Wall Oxygen Crosses".

The general principles of drawing a test's cutoff line and how to read numbers like 18.0% and 99.6% are covered more generally in "What a Test Actually Tells You — An Introduction to Sensitivity, Specificity, and Pretest Probability".

Whether to draw the normal cutoff line as a fixed ratio or a lower limit of normal, and what to do with PRISm, are issues that guidelines and studies have not yet unified into a single conclusion.

Source Papers

• "Performance and Interpretation of Office Spirometry." (2021) — PMID 34752275 — Pulmonary function tests provide both numbers and air-flow graphs together, guessing lung disease through characteristic patterns and checking reversibility.
• "Standardization of Spirometry 2019 Update. An Official American Thoracic Society and European Respiratory Society Technical Statement." (2019) — PMID 31613151 — Revised the 2005 ATS/ERS technical standards, aiming to improve measurement accuracy, precision, quality, and the patient experience.
• "Guideline for office spirometry in adults, 2012." (2012) — PMID 23237126 — South African office spirometry guideline, continuing the test until at least 3 acceptable curves (with 2 of them meeting repeatability) are obtained, classifying according to guidelines.
• "Spirometry and Bronchodilator Test." (2017) — PMID 28416951 — A review article on pulmonary function tests and bronchodilator tests published in the 2017 Journal of the Korean Academy of Tuberculosis and Respiratory Diseases, repeating up to 8 times until meeting reproducibility criteria, securing test quality before interpretation, adopting a fixed predicted value instead of the lower limit of normal for convenience, bronchodilator tests helping diagnose and evaluate asthma and COPD when obstruction is present, and a positive response commonly being an increase in FEV1 or FVC of 12% or more and 200 mL or more.
• "Primary care spirometry." (2008) — PMID 18166597 — Primary care spirometry is a valuable tool for evaluating respiratory symptoms (diagnosing and ruling out COPD, confirming asthma, treatment effects), with reports showing a low proportion of acceptable tests in primary care, affecting validity and clinical judgment.
• "Reference Values." (2025) — PMID 40769600 — Reference equations define the range expected for healthy individuals, interpretable like pediatric growth charts, containing height, sex, and age, with race-specific equations no longer recommended because the harms outweigh the benefits.
• "Association Between Preserved Ratio Impaired Spirometry and Clinical Outcomes in US Adults." (2021) — PMID 34905031 — 9 US general population cohorts, PRISm defined as FEV1/FVC ≥ 0.70 and FEV1 < 80% predicted, age- and smoking-adjusted mortality 29.6 vs 18.0 per 1,000 person-years, a small but significant increase in risk, with additional research needed on causality.
• "Prevalence of preserved ratio impaired spirometry and restrictive spirometry pattern in the general population: a systematic review and multi-level meta-analysis of studies from multiple countries." (2026) — PMID 41891755 — 57 papers from 31 countries, GOLD-defined prevalence of PRISm (FEV1 < 80% predicted, ratio ≥ 0.7) 10.60%.
• "ERS/ATS technical standard on interpretive strategies for routine lung function tests." (2022) — PMID 34949706 — Filtering out unusually low or high results using the normal range of a healthy reference population, updating the interpretation of bronchodilator response and severity, conclusion: considering clinical expertise together with the biological variability of the test and uncertainty of the results.
• "The Evolving Role of Pulmonary Function Interpretation: Clinical Implications of the New ERS/ATS Standards in Asthma Care." (2025) — PMID 40084848 — 2022 standards: GLI reference values, race-neutral equations, z-scores instead of % of predicted, redefining bronchodilator response criteria, acknowledging PRISm, with challenges remaining for clinical adoption.
• "Pulmonary Function Tests: Easy Interpretation in Three Steps." (2024) — PMID 38999220 — The ERS/ATS update is a shift from definitive diagnosis to a probabilistic approach using z-scores and the lower limit of normal, criticizing reliance on fixed ratios, with the challenge of consistency among reference equations.
• "Reference values for spirometry and their use in test interpretation: A Position Statement from the Australian and New Zealand Society of Respiratory Science." (2016) — PMID 27457870 — Adopted GLI 2012, recommending interpretation using the lower limit of normal and z-scores whenever possible.
• "GOLD Science Committee recommendations for the use of pre- and post-bronchodilator spirometry for the diagnosis of COPD." (2025) — PMID 39638416 — GOLD confirms a COPD diagnosis with post-bronchodilator FEV1/FVC < 0.7, ruling out with pre-medication values and confirming with post-medication values, repeating results near the baseline, and flow responders whose post-medication value becomes 0.7 or higher need to be monitored because they have a high likelihood of developing obstruction during follow-up.
• "Application of Global Lung Function Initiative Global Spirometry Reference Equations across a Large, Multicenter Pulmonary Function Lab Population." (2024) — PMID 37523681 — Reanalysis of 109,447 cases, changing reference equations significantly alters interpretation categories, requiring them to be read within an appropriate clinical context.
• "Comparison of GLI-Global and PLATINO spirometry equations for disease identification and staging in a Mexican-Hispanic population." (2026) — PMID 42556745 — 1,236 people in Mexico, the two reference equations are not interchangeable, with 12 to 35% reclassification of patterns and severity.
• "It is high time to discard a cut-off of 0.70 in the diagnosis of COPD." (2024) — PMID 39189795 — Review and expert opinion, 0.70 may catch only late stages and miss early stages, requiring a comprehensive approach combining symptoms, various physiological tests, and imaging.
• "Clinical relevance of fixed ratio vs lower limit of normal of FEV1/FVC in COPD: patient-reported outcomes from the CanCOLD cohort." (2015) — PMID 25583891 — 4,882 adults aged 40 and older in Canada, airflow limitation fixed ratio 17% vs lower limit of normal 11%, people caught only by the fixed ratio having odds of poor outcomes that are mostly small and nonsignificantly increased, suggesting guidelines be reconsidered to require both a low ratio and a low FEV1.
• "[Annual advances in clinical applications of pulmonary function testing 2025]." (2026) — PMID 41912392 — In lifetime trajectory charts, FEV1/FVC gradually declines starting from age 4.
• "Comparison of the prevalence of chronic obstructive pulmonary disease diagnosed by lower limit of normal and fixed ratio criteria." (2009) — PMID 19654942 — Regional sample, COPD prevalence in those over 45 years old lower limit of normal 10.9% vs fixed ratio 15.5%, age 65 and older 14.9% vs 31.1%, risk of overdiagnosis in the elderly.
• "Comparison of the lower confidence limit to the fixed-percentage method for assessing airway obstruction in routine clinical practice." (2011) — PMID 21605485 — 27,307 adult male cases, fixed ratio overdiagnosing middle-aged and older men and underdiagnosing young men, concluding that evaluation must be done using the lower limit of normal.
• "Young and middle-aged adults with airflow limitation according to lower limit of normal but not fixed ratio have high morbidity and poor survival: a population-based prospective cohort study." (2018) — PMID 29449425 — 95,288 people in the Copenhagen general population, 1% who are normal by fixed ratio but below the lower limit of normal have an increased risk of pneumonia, heart failure, and death.
• "Overdiagnosing subjects with COPD using the 0.7 fixed ratio: correlation with a poor health-related quality of life." (2011) — PMID 21183609 — 3,802 people aged 40 to 80 in Spain, the group caught only by the ratio having worse quality of life but no difference in exacerbations, 6-minute walk, physical activity, systemic biomarkers, or cardiovascular risk.
• "Use of flow volume curve to evaluate large airway obstruction." (2022) — PMID 35130676 — Flow-volume loops plot airflow according to lung volume during maximum inhalation and exhalation, especially helpful for diagnosing upper airway obstruction and guessing its location, also helping check bronchodilator response, and interpreted by looking at numbers, flow-volume, and volume-time curves together.
• "Diagnostic Value of the Maximal Expiratory Flow-Volume Curve for Central Airway Obstruction." (2025) — PMID 40786950 — Retrospective analysis of 59 patients at one hospital, plateau shapes on the exhalation side not being specific to central airway obstruction and seen even in people without obstruction, strongly suggesting obstruction when viewed together when PEF, FEF25, and their values relative to predicted are significantly low.
• "Detection of upper airway obstruction with spirometry results and the flow-volume loop: a comparison of quantitative and visual inspection criteria." (2009) — PMID 19327182 — 475 loop cases at Cleveland Clinic, confirmation criteria being bronchoscopy, laryngoscopy, and neck/chest CT, individual criteria having low diagnostic performance (AUC < 0.522), quantitative criteria having low sensitivity but being better than visual inspection criteria, requiring additional criteria.
• "Interpreting pulmonary function tests: recognize the pattern, and the diagnosis will follow." (2003) — PMID 14621232 — First determining the pattern (obstructive, restrictive, normal), pulmonary function tests by themselves not sorting out the cause, and interpreted in light of medical history, physical examination, and auxiliary tests.
• "The Concavity of the Maximal Expiratory Flow-Volume Curve Reflects the Extent of Emphysema in Obstructive Lung Diseases." (2019) — PMID 31511572 — A concave maximal expiratory flow-volume curve is a pulmonary function test characteristic of COPD.
• "Prevalence of restrictive lung function in children and adults in the general population." (2023) — PMID 36870424 — 8,891 people in a single-center population study, indirectly evaluated with restrictive pulmonary function test patterns when lung volume measurements are absent, positive predictive value for predicting actual restriction (total lung capacity < lower limit of normal) 18.0% and negative predictive value 99.6%, requiring direct lung volume measurement for diagnosis.
• "Lung Volumes." (2025) — PMID 40769589 — Methods for measuring lung volumes using pulmonary function tests, plethysmography, gas dilution, and imaging, helping distinguish restrictive and obstructive patterns.
• "Lung volumes and airway resistance in patients with a possible restrictive pattern on spirometry." (2016) — PMID 27812633 — 300 adults with suspected restriction, actual restriction 36%, obstruction or mixed 40%, nonspecific 24%, 50.3% being obese and obesity associated with all patterns, lung volume and airway resistance measurements frequently needed, and obstruction being common.
• "Routine pulmonary lung function tests: Interpretative strategies and challenges." (2024) — PMID 39644209 — Summarizing ERS/ATS 2022 interpretation steps, with mixed-type classification and severity remaining uncertain.
• "Prevalence of preserved ratio impaired spirometry: A systematic review and meta-analysis." (2026) — PMID 41777125 — PRISm pooled prevalence 10%, with trajectories being heterogeneous: return to normal 10 to 50%, maintenance 20 to 60%, and progression to COPD 6 to 53%.
• "Preserved Ratio Impaired Spirometry Prevalence, Risk Factors, and Outcomes: A Systematic Review and Meta-Analysis." (2025) — PMID 39742912 — PRISm pooled prevalence 12%, associated with increased all-cause, cardiovascular, and respiratory mortality.
• "Assessment of Preserved Ratio Impaired Spirometry (PRISm) Based on Different Definitions in the Early COPD Cohort." (2025) — PMID 40453983 — PRISm prevalence 2.0 to 12.5% depending on definition and reference equations, raising concerns about the interchangeability of definitions and reference equations.
• "Definitions of early COPD and predictors for disease progression: a systematic review." (2026) — PMID 41813011 — Terms and definitions such as PRISm, GOLD 0, and pre-COPD being heterogeneous, requiring consensus.
• "Association of preserved ratio impaired spirometry with mortality: a systematic review and meta-analysis." (2023) — PMID 37914194 — 8 population-based cohorts, PRISm associated with an increased risk of all-cause, cardiovascular, and respiratory mortality.
• "Association of preserved ratio impaired spirometry with mortality and cardiovascular diseases: a systematic review and meta-analysis." (2024) — PMID 38971833 — 8 observational cohorts, PRISm associated with an increased risk of all-cause, cardiovascular, and respiratory mortality.
• "Longitudinal mortality of preserved ratio impaired spirometry in a middle-aged Asian cohort." (2023) — PMID 37138264 — Korean regional middle-aged cohort average 16.5 years, all-cause and cardiovascular mortality of PRISm not significantly increased compared to the normal group, requiring research to distinguish low-risk subgroups.
• "Prevalence, risk factors, and clinical implications of preserved ratio impaired spirometry: a UK Biobank cohort analysis." (2022) — PMID 34739861 — 351,874 people in the UK, PRISm 11.0%, strongly associated with obesity, smoking, and asthma diagnosis, increased mortality seemingly not explained by smoking, obesity, or pre-existing lung disease, and temporary for many people.
• "Exploring Current Concepts and Challenges in the Identification and Management of Early-Stage COPD." (2023) — PMID 37629335 — GOLD proposed pre-COPD and PRISm concepts, but neither has been universally accepted in the medical community.
• "A Race-neutral Approach to the Interpretation of Lung Function Measurements." (2023) — PMID 36383197 — Development of GLI global (2022) equations, noting that any reference equation has limitations, so an individual's symptoms and medical history must be carefully considered when using them for clinical, employment, or insurance decisions.