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Office spirometry
AUTHOR: David A Kaminsky, MD
SECTION EDITOR: Meredith C McCormack, MD, MHS
DEPUTY EDITOR: Paul Dieffenbach, MD
All topics are updated as new evidence becomes available and our peer review process is complete.
Literature review current through: Jun 2023.
This topic last updated: Mar 07, 2023.
INTRODUCTION
Spirometry is used to measure forced expiratory flow rates and volumes. It is the most
commonly used pulmonary function test and is useful in the evaluation of patients with
respiratory symptoms (eg, dyspnea, cough, wheeze), and the monitoring of lung function in
patients with lung disease, being treated with drugs that can affect lung function, or at risk
of lung disease (eg, smoking, occupational exposures, family history).
In the office setting, spirometry is typically used to detect, confirm, and monitor obstructive
airway diseases (eg, asthma, chronic obstructive pulmonary disease [COPD]) and monitor
known restrictive lung disease [1-5]. In this setting, the clinician must be knowledgeable
about issues related to equipment, performance of the forced expiratory maneuver, and
interpretation of the data to obtain reliable and clinically useful information [6-8].
International guidelines for performance of office spirometry have been published [9,10].
Spirometry is not recommended as a screening test for asymptomatic adults [4,11], but
rather facilitates diagnosis of respiratory diseases.
The performance of spirometry in the office setting will be reviewed here. More general
issues related to pulmonary function tests, the interpretation of flow volume loops, and the
technique of bronchoprovocation testing are discussed separately. (See "Overview of
pulmonary function testing in adults" and "Flow-volume loops" and "Bronchoprovocation
testing".)
ADVICE RELATED TO COVID-19 PANDEMIC
Spirometry and other pulmonary function test (PFT) maneuvers can promote coughing and
aerosol generation and could lead to spread of coronavirus disease 2019 (COVID-19; SARSCoV-2) by infected patients. It is difficult to screen patients for active COVID-19 infection,
particularly those with underlying respiratory symptoms, and infected but asymptomatic
patients can shed the virus. Thus, we agree with expert recommendations that spirometry
and other PFTs be limited to patients in whom results are essential to immediate
management decisions [12,13]. Use of nebulizers to administer bronchodilators or
methacholine should be avoided.
Measures to prevent spread of COVID-19 should include hand hygiene and personal
protective equipment (PPE; glove, gown, face mask and shield) for staff and anyone else in
the testing space (eg, interpreters). N95 masks or powered air purifying respirators (PAPR)
are preferred over surgical masks. Patients should be brought to a testing room using an
approach that avoids queuing or grouping individuals in a waiting area and that allows
adequate time between patients for sufficient air exchange. Enhanced cleaning of the
testing area should be performed between patients.
EQUIPMENT
Office spirometers should meet equipment specifications as described in international
guidelines [5,10,14,15]. The majority of spirometers manufactured since 1990 are accurate,
although some flow-sensing office spirometers can produce falsely high results [16-18].
Reference standards are discussed separately. (See "Selecting reference values for
pulmonary function tests".)
To avoid cross-contamination between patients when using permanent flow sensors, it is
preferable to employ single use disposable flow sensors that practically eliminate the risk of
inhalational cross contamination. Disposable one-way mouthpieces may also be used;
otherwise, patients should be instructed not to inhale from the spirometer when only forced
exhalation maneuvers are being obtained.
Volume sensing spirometers maintain accuracy over many years but are more difficult to
clean and are rarely used for office spirometry.
QUALITY CONTROL
Office spirometers should accurately measure the forced expiratory volume in one second
(FEV1), forced expiratory volume in six seconds (FEV6), and forced vital capacity (FVC) and also
provide quality checks and error messages. A survey of 17 spirometers used in primary care
offices found only 1 of 17 met accuracy criteria; clearly manufacturers and practitioners need
to be aware of potentially significant quality issues related to office spirometry [19].
In addition to internal calibration performed by the device, daily calibration checks with a
three liter syringe are recommended [10]. When performing a calibration check, the threeliter syringe should be discharged into the spirometer three times. The volumes read by the
machine should be within 3 percent of three liters. If the spirometer reading remains outside
these limits after replacing the flow sensor, the device should be removed from use until
checked by the manufacturer.
It is also essential that the nurse or technician enter correct values for age, height, and sex at
birth, as these values are used to generate the appropriate predicted values for the
individual patient. Height should be measured with shoes off, preferably using a
stadiometer, rather than relying on the patient's stated height. Percent predicted values that
are unexpectedly higher or lower than expected are a clue that an incorrect age or height
value may have been entered. Waist circumference, while not used to calculate predicted
normal values, can also be measured because abdominal obesity is a common cause of
mildly low values for FEV1 and FVC [20].
PROCEDURE
Patients are usually seated during spirometry, unless otherwise noted. Nose clips or manual
occlusion of the nares help to prevent air leakage through the nasal passages, although
spirometry can be performed without nasal occlusion [21]. The deep inhalation should occur
before the mouthpiece is placed in the mouth. Immediately after the deep inhalation, the
mouthpiece is placed just inside the mouth between the teeth. The lips should be sealed
tightly around the mouthpiece to prevent air leakage during maximal forced exhalation. The
patient should then be instructed to blast out the air without hesitation (within two seconds
of reaching full inflation). Exhalation should last until a plateau in exhaled volume is reached,
or a maximum of 15 seconds. However, if measuring FEV6 as a surrogate for FVC, then
exhalation need only last at least six seconds. To fully evaluate flow volume loops, it is
necessary to perform a complete inspiratory maneuver at the end of the test. The maximal
inspiration at the end of test requires vigorous coaching to achieve good quality results and
patients should be informed that this aspect of the maneuver feels somewhat
uncomfortable. (See "Flow-volume loops".)
The patient is allowed to rest for several seconds and the procedure is repeated. Usually,
three maneuvers are performed, although additional tests may be needed if one or more of
the curves are unacceptable.
COACHING THE PATIENT
The most important task of the technician or person performing the test is to obtain
maximal, reproducible efforts from the patient.
Even with the use of accurate instruments, office spirometry results may be misleading if the
patient's efforts are submaximal. Unlike most other medical tests in which the patient
remains passive, accurate spirometry results require significant exertion on the part of the
patient.
The technician must instruct and encourage the patient to perform the breathing maneuvers
in three phases (
figure 1):
●
Phase 1: Coach the patient to take as deep a breath as possible
●
Phase 2: Strongly prompt the patient to blast out the air into the spirometer without
hesitation after reaching a full inspiration
●
Phase 3: Encourage the patient to continue exhaling until a plateau in exhaled volume
or 15 seconds is reached, unless just measuring FEV6 in which case the exhalation
should last at least six seconds (three seconds for children)
Patients in whom a flow volume loop is needed will need to perform an additional phase of
deep and forceful inspiration to total lung capacity immediately after phase 3.
ADEQUACY OF TEST
An adequate test usually requires three acceptable and repeatable forced vital capacity (FVC)
maneuvers [10]. The clinician and technician must learn to recognize the patterns of
acceptable and unacceptable efforts, since poorly performed maneuvers often mimic
disease patterns. Detection of poorly performed maneuvers requires direct inspection of
both flow-volume curves and volume-time spirograms (
figure 2) [14,22].
An acceptable maneuver requires a sharp peak in the flow curve and an expiratory duration
that reaches a plateau of exhaled volume or 15 seconds, or greater than six seconds if
measuring FEV6 instead of FVC (
figure 3). At least three acceptable maneuvers should be
available for analysis.
Repeatability is determined by comparing the FVC and FEV1 values of the maneuvers. The
two highest values for FVC and for FEV1 should be within 0.15 L of each other (for adults; the
limit is 0.10 L for children) [10,23].
The grading system for the quality of spirometry factors in the number of acceptable
maneuvers and the degree of repeatability for FEV1 and FVC separately (
table 1) [10].
INTERPRETATION
All tracings from the forced expiratory maneuvers should be examined for acceptability and
repeatability, according to the criteria mentioned above. The study should then be classified
as normal or abnormal, the latter showing an obstructive, a possible restrictive, or a possible
mixed pattern. Lung volumes are necessary to confirm whether or not the patient has a
restrictive deficit. The severity of the ventilatory impairment is then assessed, according to
the algorithm (
algorithm 1). (See 'Forced expiratory volume in one second' below and
"Overview of pulmonary function testing in adults".)
Forced vital capacity — The forced vital capacity (FVC) (also known as the forced expiratory
volume) is the maximal volume of air exhaled with a maximally forced effort from a position
of full inspiration and is expressed in liters [10]. The highest FVC from the three acceptable
forced expiratory maneuvers is used for interpretation [10].
The FVC may be reduced by suboptimal patient effort, airflow limitation, restriction (eg, from
lung parenchymal, pleural, or thoracic cage disease), or a combination of these
(
algorithm 1). In general, a low FVC needs further evaluation with full pulmonary function
tests to determine whether lung restriction is present [24]. Patients with obstruction and low
FVC frequently demonstrate air trapping or failure to complete a full exhalation rather than
an additional restrictive process. (See "Overview of pulmonary function testing in adults".)
When FVC is low, restriction is not confirmed by lung volumes, and there is not obstruction
(based on FEV1/FVC), this represents a "nonspecific" pattern. Nonspecific patterns are not
clearly indicative of any lung disease subtype but may be associated with either ongoing or
future obstructive or restrictive diseases [25]. Repeat testing to reassess lung function after
several months to a year may be useful.
Due to these potential problems with air trapping and incomplete exhalation, FVC is not
used to grade restriction severity. We prefer to assess the severity of restrictive deficits by
applying the z-score approach to total lung capacity measurements, when available. If lung
volumes are not available, FEV1 may be used to assess the severity of previously established
restriction, as was recommended in prior guidelines [23]. (See "Overview of pulmonary
function testing in adults".)
The slow vital capacity (SVC) is the maximal volume of air exhaled after a maximal
inspiration, but without a forced effort. The SVC is rarely measured outside of hospital-based
pulmonary function labs. For normal subjects, the slow and forced vital capacities are very
close, whereas patients with airflow limitation tend to have a lower FVC than SVC. (See
"Overview of pulmonary function testing in adults", section on 'Spirometry'.)
Forced expiratory volume in six seconds — The forced expiratory volume in six seconds
(FEV6) is sometimes used as a surrogate for FVC [21,26]. The FEV6 has the advantage of being
more reproducible than the FVC and less physically demanding for the patient.
Forced expiratory volume in one second — The forced expiratory volume in one second
(FEV1) is the maximal volume of air exhaled in the first second of a forced exhalation that
follows a full inspiration, expressed in liters [21]. The FEV1 reflects the average flow rate
during the first second of the FVC maneuver. The FEV1 is the most important spirometric
variable for assessment of the severity of airflow obstruction (
algorithm 1). The highest
FEV1 from the three acceptable forced expiratory maneuvers is used for interpretation, even
if it does not come from the maneuver with the highest FVC [10].
In patients with asthma, the FEV1 typically declines with clinical worsening of airways
obstruction and increases with successful treatment of airways obstruction. The FEV1 should
be used for determining the degree of obstruction (mild, moderate, or severe) and for serial
comparisons when following patients with asthma or chronic obstructive pulmonary disease
(COPD).
FEV1 may also be used to grade the severity of restrictive or mixed obstructive/restrictive
disorders once restriction has been confirmed by lung volumes; however, we prefer to grade
pure restriction using total lung capacity when this measurement is available
(
algorithm 1) [23]. (See "Overview of pulmonary function testing in adults".)
The measured FEV1 should be reported based on z-score, instead of percent predicted. This
measurement strategy helps to avoid age, sex, and height bias and is associated with
important clinical outcomes [27,28]. The lower limit of normal (LLN) for FEV1 and other
spirometry measures is defined by z-score <-1.645, which is equivalent to the fifth percentile
in the distribution of healthy never-smokers. This replaces using a fixed percent of predicted
value, which does not incorporate demographic features [27,29]. An FEV1 within the normal
range may still represent a mild ventilatory impairment if obstruction or restriction is
confirmed using other measures.
Reference equations from the Global Lung Function Initiative, which assessed healthy
individuals age 3 to 95 years across ethnic and geographic groups in 26 countries, are
recommended for both pediatric and adult patients [27,30]. These reference equations are
endorsed by multiple international expert groups and replace the older generation of
equations, including those derived from the NHANES III study [23,31]. (See "Selecting
reference values for pulmonary function tests".)
As a rough guideline, the predicted FEV1 for a 50-year-old of average height is about 4 L for a
male and 3 L for a female. When predicted values have not been calculated, patients with
severe COPD generally have an FEV1 less than one liter, while those with moderate COPD
have an FEV1 between 1 and 1.5 liters. Individuals with an FEV1 ≤75 percent of predicted are
more likely to report dyspnea, wheezing, or cough, than those with an FEV1 >75 percent
predicted [32]. (See "Selecting reference values for pulmonary function tests".)
Ratio of FEV1/FVC — The FEV1/FVC ratio is the fraction of the forced vital capacity that can
be exhaled in the first second. It is the most important parameter for detecting airflow
obstruction in diseases like asthma and COPD (
algorithm 1). However, once it has been
determined that a patient has airways obstruction, the FEV1/FVC ratio is not useful for
gauging severity of disease, since the FVC often decreases with increasing obstruction due to
air trapping or premature termination of exhalation. The FEV1, not the FEV1/FVC ratio, should
be used to monitor patients with asthma or COPD. (See "Pulmonary function testing in
asthma" and "Chronic obstructive pulmonary disease: Diagnosis and staging".)
The use of z-score <-1.645 or the fifth percentile LLN for FEV1/FVC to detect airway
obstruction reduces the misclassification associated with using a fixed threshold of 0.7
[29,33-36].
If FEV1/FVC is low, but FEV1 is normal, this is still considered indicative of mild airflow
obstruction. In some cases, a low FEV1/FVC in the presence of a low FEV1 is classified as
reflecting dysanapsis, or airways size being too small relative to lung volume size. While
dysanapsis may be a physiologically normal variant, it has also been associated with COPD
[37], bronchodilator responsiveness, and [38] severe asthma in children with obesity [39].
If FEV1/FVC is normal, but FEV1 is low, this may represent restriction, which should be
evaluated by lung volumes. When lung volumes are not available, this pattern has also been
labeled "Preserved Ratio Impaired Spirometry", or PRISm. It is unclear if PRISm is a distinct
phenotype of lung disease, but multiple studies have demonstrated that PRISm is associated
with increased cardiopulmonary disease and mortality [40-42].
When FVC maneuvers are routinely stopped after six seconds, the FEV1/FEV6 may replace the
FEV1/FVC [43]. The advantages of the FEV1/FEV6 include less frustration for the patient and
technician trying to achieve an end-of-test plateau, less chance of syncope, shorter testing
time, and better repeatability, without loss of sensitivity or specificity [26,44-46]. The
appropriate lower limit of normal for FEV1/FEV6 from NHANES III should be used [31,47];
unfortunately, the GLI equations do not include prediction equations for FEV6.
Other flow measures — The transition from normal function to moderate airflow
obstruction is generally gradual. Physiologists have searched for a test that is more sensitive
than the FEV1 for detection of airflow obstruction in its early stages. None has proven to be
as reliable as the index obtained by dividing the FEV1 by the FVC. The forced expiratory flow
between 25 and 75 percent of the FVC (also known as FEF25-75 or maximal mid-expiratory
flow rate) should not be used to detect "small airways disease" in adults, due to poor
specificity and reproducibility [21].
Choosing the best values — Report the highest FVC and the highest FEV1 from three
spirometric maneuvers, even if they are derived from different maneuvers [10].
Flow-volume loops — The flow-volume loop is a plot of inspiratory and expiratory flow (on
the Y-axis) against volume (on the X-axis) during the performance of maximally forced
inspiratory and expiratory maneuvers. Changes in the contour of the loop can detect upper
airway obstruction. The analysis of flow-volume loops is discussed separately. (See "Flowvolume loops".)
Post-bronchodilator spirometry — In patients who have evidence of airflow limitation on
baseline spirometry, and no prior diagnosis of asthma or COPD, post-bronchodilator
spirometry may be useful. If post-bronchodilator spirometry is normal, COPD is less likely.
The assessment of bronchodilator responses in patients with asthma-like symptoms is
described separately. Note, however, that a bronchodilator response alone does not
distinguish asthma from COPD [48]. If the change in spirometry post-bronchodilator does
not support a diagnosis of obstructive lung disease, referral for bronchial challenge testing
(eg, with methacholine or exercise) may be helpful [49]. (See "Pulmonary function testing in
asthma", section on 'Bronchodilator responses'.)
LIMITATIONS
Office spirometry has some important limitations, even when all of the above-described
quality measures are employed. As examples:
●
Abnormal spirometry results have little if any value in prompting smokers to quit [5054]. All patients who smoke should be advised to stop smoking and provided smoking
cessation assistance.
●
In a patient with asthma, which is characterized by variability in clinical symptoms and
airflow obstruction, normal airflow at the time of office visits does not exclude airflow
obstruction at other times.
●
Patients with early interstitial lung disease may have normal spirometry and need
further testing of gas transfer with a diffusing capacity of the lungs for carbon
monoxide (DLCO) and/or exercise oximetry to identify the cause of dyspnea [55].
●
Misclassification rates due to suboptimal spirometry performance or interpretation are
relatively high in the office setting [7,19,56]. Among eight general practices, rates for
successfully meeting American Thoracic Society (ATS) quality standards were below 80
percent [7]. In 16 primary care offices involving 17 different spirometers, only 60
percent of patients had spirometry that met acceptability criteria [19]. Therefore,
continuous quality review and feedback to nurses and technologists performing office
spirometry are necessary and results should be verified by repeat testing in a
Pulmonary Function Test (PFT) laboratory when important clinical decisions will be
made based on the results [57,58].
●
There are multiple barriers to performing in-office spirometry. One comprehensive
survey identified multiple barriers including lack of knowledge about how to interpret
spirometry, lack of resources (equipment, personnel, skills, time), and lack of belief in
importance of results [59]. Most of the barriers identified were also true for out-ofoffice (ie, hospital) spirometry, indicating that implementing spirometry in general
faces many challenges.
RISKS
Spirometry is a low-risk procedure and has few side effects [14]. During the test, some
patients may experience dizziness. The forced expiratory maneuver causes an increase in the
pressure in the chest, abdomen, head, and eyes. In general, patients who have recently (eg,
less than six weeks) had abdominal, intracranial, or eye surgery or a pneumothorax should
not perform spirometry, although data are limited.
Spirometry requires exertion and should be avoided in patients with unstable angina or a
recent myocardial infarction.
Rarely, performance of a forced expiratory maneuver will precipitate acute
bronchoconstriction. This seems more likely to occur when a patient's asthma or COPD is
poorly controlled. Treatment includes administering inhaled albuterol and supplemental
oxygen.
MONITORING
Office spirometry is also useful for monitoring control of asthma The National Asthma
Education and Prevention Program advises the following frequencies for spirometry testing
when caring for patients with asthma [60]:
●
At the time of initial assessment
●
After treatment is initiated and symptoms and peak flow have stabilized
●
During periods of progressive or prolonged loss of asthma control
●
At least every one to two years
For patients with chronic obstructive pulmonary disease (COPD), repeat spirometry is
advised whenever there is a substantial increase in symptoms or decrease in exercise
tolerance [4,61,62].
SOCIETY GUIDELINE LINKS
Links to society and government-sponsored guidelines from selected countries and regions
around the world are provided separately. (See "Society guideline links: Pulmonary function
testing".)
SUMMARY AND RECOMMENDATIONS
●
Spirometry is used to detect and monitor obstructive airway disease in patients with
respiratory symptoms and risk factors. (See 'Introduction' above.)
●
Office spirometers should accurately measure the forced expiratory volume in one
second (FEV1) and either the forced vital capacity (FVC) or the forced expiratory volume
in six seconds (FEV6). Calibration checks should be performed daily with a three-liter
syringe. (See 'Quality control' above.)
●
Since poorly performed maneuvers often mimic disease patterns, the clinician and
technician must learn to recognize the patterns of unacceptable efforts (
figure 2).
(See 'Quality control' above.)
●
An acceptable maneuver requires a sharp rise in the flow volume curve to the peak flow
and an expiratory duration that reaches a plateau in expired volume or a duration of 15
seconds; however, if FEV6 is being measured instead of FVC, then only a duration of at
least six seconds is required. At least three good quality maneuvers should be
performed. (See 'Quality control' above.)
●
Report the highest FVC and the highest FEV1 from three spirometric maneuvers, even if
they are derived from different maneuvers. The fifth percentile lower limit of normal
(LLN) for FEV1/FVC is preferred over the fixed threshold of 0.7 because it reduces the
misclassification rate for detecting airway obstruction. (See 'Choosing the best values'
above and 'Ratio of FEV1/FVC' above.)
●
Reduction of the FEV1/FVC suggests airway obstruction (
algorithm 1) (see
'Interpretation' above). If FEV1/FVC is low but FEV1 is normal, this is still considered
obstruction but may also represent dysanapsis, which can be a normal variant.
●
A normal FEV1/FVC but reduced FVC suggests restriction, which must be confirmed by
lung volume measurement. If restriction is not confirmed, this pattern has been
termed "nonspecific". If lung volumes are not available, a low FEV1 and normal
FEV1/FVC has also been referred to as Preserved Ratio Impaired Spirometry, or PRISm.
●
The FEV1/FEV6 can be helpful instead of FEV1/FVC when the FVC maneuvers are
routinely stopped after six seconds. (See 'Ratio of FEV1/FVC' above.)
●
The FEV1 should be used for determination of the degree of impairment and for serial
comparisons in obstructive and mixed obstructive-restrictive disorders. It may also be
used in the absence of lung volumes for grading previously confirmed restriction.
FEV1/FVC ratio is not useful for gauging severity of ventilatory impairment, since the
FVC often decreases with increasing obstruction due to air trapping or premature
termination of exhalation (
●
algorithm 1). (See 'Interpretation' above.)
Office spirometry results should be verified by formal testing in a pulmonary function
test (PFT) laboratory when important clinical decisions will be made based on the
results. (See 'Interpretation' above.)
●
Despite the potential benefits, ongoing barriers to office spirometry implementation
include primary care provider uncertainty regarding the benefits of testing, lack of
resources, and lack of confidence in spirometric interpretation.
ACKNOWLEDGMENT
The UpToDate editorial staff acknowledges Paul Enright, MD, who contributed to earlier
versions of this topic review.
Use of UpToDate is subject to the Terms of Use.
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Topic 6968 Version 29.0
GRAPHICS
Technique for performing spirometry
Unlike most other medical tests in which the patient remains passive,
accurate spirometry requires a coordinated maximum effort. The
technician should instruct and encourage the patient to perform the
breathing maneuvers in three phases: Phase 1: coach the patient to
take as deep a breath as possible; Phase 2: loudly prompt the patient
to BLAST out the air into the spirometer; Phase 3: encourage the
patient to continue exhaling for several more seconds.
Graphic 55460 Version 1.0
Unacceptable spirometry
Flow-volume curve patterns from unacceptable forced vital capacity
maneuvers. Curve A (red) hesitating start; curve B (blue) submaximal
blast (poor peak flow effort); curve C (green) excessive coughing at
the beginning of the maneuver; curve D (orange) premature
termination of effort.
FVC: forced vital capacity.
Graphic 57832 Version 2.0
Flow-volume curve variations
Flow-volume curves from (A) a healthy person or from patients with
(B) severe obstruction (emphysema), (C) severe restriction from
interstitial disease (radiation fibrosis), (D) fixed central airway
stenosis (or variable intrathoracic airway obstruction), and (E) poor
effort.
Graphic 65057 Version 2.0
Grading system for repeatability of FEV1 and FVC (graded separately)
Grade
Number of
measurements
Repeatability:
Age >6 years
Repeatability:
Age ≤6 years*
A
≥3 acceptable
Within 0.150 L
Within 0.100 L*
B
2 acceptable
Within 0.150 L
Within 0.100 L*
C
≥2 acceptable
Within 0.200 L
Within 0.150 L*
D
≥2 acceptable
Within 0.250 L
Within 0.200 L*
E
≥2 acceptable
>0.250 L
>0.200 L*
or 1 acceptable
N/A
N/A
U
0 acceptable and ≥1
usable
N/A
N/A
F
0 acceptable and 0
usable
N/A
N/A
The repeatability grade is determined for the set of prebronchodilator maneuvers and the set of
post-bronchodilator maneuvers separately. The repeatability criteria are applied to the
differences between the two largest FVC values and the two largest FEV1 values. Grade U
indicates that only usable but not acceptable measurements were obtained. Although some
maneuvers may be acceptable or usable at grading levels lower than A, the overriding goal of the
operator must be to always achieve the best possible testing quality for each patient.
FEV1: Forced expiratory volume in one second; FVC: forced vital capacity; N/A: not applicable.
* Or 10% of the highest value, whichever is greater; applies for age 6 years or younger only.
Reprinted with permission of the American Thoracic Society. Copyright © 2020 American Thoracic Society. All rights
reserved. From: Graham BL, Steenbruggen I, Miller MR, et al. Standardization of Spirometry 2019 Update. An Official
American Thoracic Society and European Respiratory Society Technical Statement. Am J Respir Crit Care Med 2019;
200:e70. The American Journal of Respiratory and Critical Care Medicine is an official journal of the American Thoracic
Society.
Graphic 129852 Version 1.0
Classification and grading of ventilatory impairments based on spirometry [1
FEV1: forced expiratory volume in one second; FVC: forced vital capacity; LLN: lower limit of normal, the
5th percentile.
* Low refers to levels below the 5th percentile, or a z-score <–1.645; absolute values are not used due to
changes in spirometry with age and other factors.
¶ A reduced FVC does not prove a restrictive process. Confirmation of restriction requires evaluation of
lung volumes in a pulmonary function laboratory (ie, total lung capacity z-score <–1.645 or below fifth
percentile).
Δ A reduced FVC with normal FEV1/FVC and lung-volumes is a "nonspecific" pattern that may be followed
over time. One-third of patients with nonspecific patterns develop obstructive or restrictive disease in th
next three years.
◊ Many patients with reduced FEV1/FVC and low FVC have simple obstruction with air-trapping or failure
to complete exhalation.
§ The severity of obstructive and mixed obstructive/restrictive ventilatory impairments are physiologicall
graded by decrement in FEV1. Patients with restriction should have restrictive impairment confirmed and
graded based on total lung capacity, but may be monitored by changes in FEV1. FEV1 may also be used a
an alternative method to grade severity of confirmed restriction when only spirometry or % predicted
values are available.
¥ Z-score is the preferred method for grading severity based on 2022 European Respiratory
Society/American Thoracic Society (ERS/ATS) guidelines because it reduces bias due to age, sex, and othe
factors. Some spirometry software continues to report percent predicted, so we also include
categorization based on this reporting method. The percent predicted severity classification has been
adapted from earlier guidelines and modernized by reducing the number of distinct categories.
References:
1. Stanojevic S, Kaminsky DA, Miller MR, et al. ERS/ATS technical standard on interpretive strategies for routine lung function
tests. Eur Respir J 2022; 60:2101499.
2. Pellegrino R, Viegi G, Brusasco V, et al. Interpretative strategies for lung function tests. Eur Respir J 2005; 26:948.
Graphic 139645 Version 3.0
Contributor Disclosures
David A Kaminsky, MD Other Financial Interest: MGC Diagnostics Inc [Speaker/faculty
cardiorespiratory diagnostics course]. All of the relevant financial relationships listed have been
mitigated. Meredith C McCormack, MD, MHS Consultant/Advisory Boards: Aridis [Pulmonary function
testing]; Boehringer Ingelheim [COPD and asthma]; Celgene [Asthma]; GlaxoSmithKline [Chronic
obstructive pulmonary disease]; MGC Diagnostics [Pulmonary function testing]; NDD Medical
Technologies [Pulmonary function testing]. All of the relevant financial relationships listed have been
mitigated. Paul Dieffenbach, MD No relevant financial relationship(s) with ineligible companies to
disclose.
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