Repeatable FVC and FEV1
In 2005, ATS/ERS tightened the level of consistency to be achieved among test results: additional maneuvers should be attempted if the difference between the largest and second largest values of the FVC or FEV1 exceeds 0.15 L (150 mL) among the acceptable curves. This difference between the largest and second largest values is now called “repeatability,” it was formerly termed “reproducibility,” and many spirometers label it “variability.” It is recommended that technicians strive to meet this goal during testing, attempting up to eight efforts, unless the subject is unable to continue with the test. Failure to achieve repeatability needs to be taken into account during the interpretation of results.
In the screening spirometry setting, lack of repeatability is often caused by a failure to inhale maximally to total lung capacity before each maneuver (Fig. 9). However, when FVC or FEV1 repeatability is very poor, for example, more than 0.50 L (500 mL), sensor contamination or zero-flow errors are also likely (Figs. 2 and 3). In the absence of these technical problems, failure to achieve repeatability does not rule out interpretation of results, since it may also be caused by hyperresponsive airways or other respiratory disorders. The lack of repeatability needs to be documented and taken into account during the interpretation process.
The American College of Occupational and Environmental Medicine recommends that occupational spirometry tests strive to meet ATS/ERS criteria for a valid test, that is, recording three or more acceptable curves, with FVC and FEV1 repeatability of 0.15 L (150 mL) or more. Failure to achieve repeatability in screening spirometry tests is often caused by inhalations that are not maximal. However, when flow-type spirometers are in use, very poor repeatability may indicate sensor contamination or zero-flow errors.
The largest FVC and largest FEV1 from all acceptable curves are reported as the test results even if they are drawn from different curves.4 The FEV1/FVC is calculated using these two values. To permit a thorough review of a spirometry test, it is recommended that complete results from all acceptable curves also be shown on the spirometry report. As discussed later, ATS/ERS continues to strongly discourage evaluating the forced expiratory flow (FEF) rates, but if reported, all FEF, except for the peak expiratory flow, are to be drawn from one acceptable curve with the highest sum of (FEV1 + FVC). The highest peak expiratory flow recorded from among all acceptable curves is to be reported.
The American College of Occupational and Environmental Medicine recommends that occupational spirometry test reports include values and curves from all acceptable curves and that the largest FVC and largest FEV1 be interpreted, even if they come from different curves. Default spirometer configurations need to be examined and, if possible, adjusted to meet these recommendations.
Quality Assurance Reviews
In addition to emphasizing technician training, recent ATS/ERS and ATS spirometry standardization statements strongly recommend that spirograms be reviewed periodically to provide regular feedback on the quality of each technician's testing.3,14 Quality assurance reviews can be performed on electronically saved tracings or on copies of spirograms. It is recommended that samples of randomly selected tests, all invalid tests, and tests with abnormally low or improbably high results (FEV1 or FVC > 130% of predicted) be reviewed. Because of their profound impact on test results, figures illustrating some of the technical errors that can affect spirometry test results are presented in the 1994 ATS spirometry update16 and included in Figs. 2 to 12 in this statement.
The American College of Occupational and Environmental Medicine highly recommends that facilities performing occupational spirometry tests establish on-going programs that provide quality assurance review of spirograms on a regular basis. The frequency of such reviews needs to be at least quarterly, and more often if technicians are inexperienced or if poor technical quality is observed. As recommended by the California Department of Public Health, the goal of such reviews is to maintain the technical quality of spirometry tests at a high level, assuring that 80% or more of an occupational health program's spirometry tests are technically acceptable. It is recommended that reviews be conducted by those experienced in recognizing and correcting flawed spirometry tests results.11
COMPARING RESULTS WITH REFERENCE VALUES
After establishing the technical validity of a test, spirometry results are usually evaluated at each measurement date as well as longitudinally, comparing a worker's current results with previous test results. Most available spirometer software performs a traditional (“cross-sectional”) evaluation at the time of the test, comparing the worker's results with the reference range expected for his/her current demographic characteristics. Recommendations for this approach are summarized in this section. Fewer spirometers evaluate change over time or “trending,” and criteria for longitudinal abnormality are less well established. Recommendations for longitudinal interpretation are summarized in the following section.
Three critical aspects of traditional pulmonary function evaluation influence the interpretation: (1) the source of the reference values used; (2) how the reference values are adjusted when a worker's race/ethnicity differs from the reference study subjects’; and (3) selection of the interpretation algorithm used to categorize pulmonary function as normal or abnormal, that is, the choice of lung function parameters to be evaluated and the sequence in which they are examined.
The American College of Occupational and Environmental Medicine's 2000 spirometry statement identified normal, obstructive, and restrictive impairment patterns, as well as grading the severity of those impairments. However, since 2005, several conflicting schemes are now recommended for grading severity.5,17,18 Since the most critical concern of occupational screening spirometry is to separate abnormal from normal, this ACOEM statement focuses only on that task, for which there is strong consensus. Choice of a severity-grading scheme will be left to the practitioner's discretion, depending upon the circumstances in which they are conducting spirometry tests.
Reference values define the expected average and lower boundary of the reference range for individuals with the same demographic characteristics as the worker being tested. Reference values are generated from research studies of asymptomatic never smokers of varying ages and heights, both genders, and sometimes varying ethnic/racial backgrounds. Subject ethnic/racial group is based on self-report, and height in stocking feet needs to be measured periodically. The relationships of pulmonary function parameters with these four demographic variables are summarized in regression equations, which produce average “predicted” values and fifth percentile lower limits of normal (LLN). Since predicted values and LLNs describe the average and the bottom of the reference range based on a single research study, both indices need to be drawn from a single source of reference values.5,19
Many reference value studies have been conducted in a single geographical location,20,21 but ATS/ERS,5 ACOEM,1 and the sixth edition of the American Medical Association (AMA) Guides to the Evaluation of Permanent Impairment 18 recommend using reference values generated from the 3rd National Health and Nutrition Examination Survey (NHANES III).22 The 3rd National Health and Nutrition Examination Survey studied a random sample of never smokers from across the United States, using spirometry testing of high technical quality, and including three ethnic/racial groups. Therefore, race-specific NHANES III reference equations are available for whites, African Americans, and Mexican-Americans. If the NHANES III reference values are not available on older spirometers, the Crapo reference values20 are closer to the NHANES’ values than other available prediction equations.23
The American College of Occupational and Environmental Medicine, along with ATS/ERS and the AMA guides sixth edition, endorses use of the NHANES III (Hankinson) reference values in the occupational setting, unless a regulation mandates another specific set of reference values. National Health and Nutrition Examination Survey reference values can be calculated for individuals, using a reference value calculator at www.cdc.gov/niosh/topics/spirometry/RefCalculator.html. Tables of NHANES III predicted values, but not LLNs, can be obtained at www.cdc.gov/niosh/topics/spirometry/nhanes.html. If NHANES III reference values are not available on a spirometer, ACOEM now recommends selecting the Crapo prediction equations, and only using the Knudson 1983 equations if the Crapo equations are not available. Since reference values vary significantly and may strongly affect the percent of predicted values, the selected reference values need to be documented on the spirometry printout.
Race Adjustment of Predicted Values and Lower Limits of Normals
If a worker's self-reported race/ethnicity is the same as that of the reference value group, no adjustment of the worker's reference values is required. Since NHANES III reference values were generated specifically for whites, African Americans, and Hispanics, the predicted values and LLNs are not adjusted when workers of these race/ethnicity groups are tested. However, when Asian workers (ie, Chinese, Japanese, East Indian, or Pakistani) are tested, race-specific NHANES reference values are not available. Though less desirable than race-specific values,24 white-predicted values and LLNs for FVC and FEV1 need to be multiplied by a scaling factor to account for the larger thoracic cages observed in whites when compared with Asians of the same age, height, and gender. The scaling factor recommended by ATS/ERS in 2005, 0.94, was based on two small studies5 and there is recent evidence that this factor may not be optimal. Studies reported since 2005 indicate that the previously used scaling factor of 0.88 may still be the most appropriate choice for Asians as well as for African Americans.25,26
If NHANES III reference values are not available to evaluate an African American's pulmonary function, and the only available reference values are drawn from studies of whites, for example, Crapo20 or Knudson21 predicted values, the white predicted values and LLNs for FVC and FEV1 need to be multiplied by 0.88 to obtain appropriate predicted values and LLNs for the African American employee.1,5 The single exception to this recommendation is for cotton-exposed workers for whom the Knudson 197627 prediction equations and a scaling factor of 0.85 must be used for African American workers, as mandated by OSHA.12
The American College of Occupational and Environmental Medicine and ATS/ERS recommend that race-specific NHANES III reference values be used whenever possible, basing the worker's race/ethnicity on self-report. To evaluate Asian workers, ACOEM continues to recommend that white predicted values and LLNs for FVC and FEV1 be multiplied by a scaling factor of 0.88 to obtain appropriate Asian reference values. If NHANES III reference values are not available when African American workers are tested, and white-predicted values need to be used, ACOEM recommends applying a scaling factor of 0.88 to the white-predicted values and LLNs for FVC and FEV1, unless other practices are mandated by an applicable regulation. Note that FEV1/FVC predicted values and LLNs are not race-adjusted.
For two decades, ATS has consistently recommended applying a stepwise algorithm to three pulmonary function parameters to interpret spirometry results.5,19 The American College of Occupational and Environmental Medicine endorsed this approach in its 2000 statement.1 Since consensus exists on how to distinguish normal from abnormal results, and which measurements identify obstructive or restrictive impairment, these determinations are presented in Fig. 13.
In contrast to the determination of normal/abnormal, recommendations for grading severity of impairment are now quite disparate,5,17,18 and so this statement's interpretation algorithm shown in Fig. 13 does not grade severity of impairment. As noted later, practitioners need to choose an impairment-grading scheme that is most appropriate for their specific needs.
Lower Limit of Normal Defines Abnormality
Since 1991, the ATS has officially endorsed using the fifth percentile, the point below which 5% of nonexposed asymptomatic subjects are expected to fall, as the lower limit of the reference range (LLN).19 Though two older cutoff points for abnormality have re-emerged in some chronic obstructive pulmonary disease screening recommendations, that is, 80% of the predicted value, and an observed FEV1/FVC ratio less than 0.70,28 the ATS/ERS official recommendations continue to explicitly discourage use of these definitions.5,19 As pulmonary function declines with age, the fifth percentile LLN also declines, labeling only 5% of normal individuals in each age group as “abnormal.” In contrast, as age increases, increasing proportions of nonexposed healthy individuals fall below 80% of predicted or a measured FEV1/FVC ratio of 0.70, creating an increasing pool of false positives in an aging workforce.19,29,30 These fixed definitions of abnormality also yield some false negatives in young workers. As recommended by the ATS since 1991,5,19 using the fifth percentile LLN to define abnormality for the major spirometry measurements avoids these problems. As described later, the LLN is used to identify both obstructive and restrictive impairment patterns.
As shown in Fig. 13, the first step in interpreting spirometry test results is to determine whether a valid test has been performed or if more maneuvers may be needed. Once test validity has been established, Step 2 shows that the FEV1/FVC is the first measurement to be evaluated, to “distinguish obstructive from nonobstructive patterns.”19 When the FEV1/FVC and FEV1 are both less than their LLNs, airways obstruction is present. However, when FEV1/FVC is less than LLN, but FEV1 is more than its LLN, borderline obstruction or a normal physiologic variant may exist. The ATS/ERS cautions that an FEV1/FVC below the LLN combined with FVC and FEV1 more than 100% of predicted is “sometimes seen in healthy subjects, including athletes” and may be due to dysanaptic growth of the alveoli. This pattern is labeled as a possible “normal physiologic variant,”5,19 and is not unusual among physically fit nonsmoking emergency responders, firefighters, and police. However, if these healthy workers are exposed to known hazardous substances, the possibility of obstructive impairment needs to be considered when a reduced FEV1/FVC is observed.
Though not included in Fig. 13, all grading schemes for severity of airways obstruction rely on the FEV1 percent of predicted, applying one of several definitions, whose “number of categories and exact cutoff points are arbitrary.”5,17,18 Widely used schemes are based on the 1986 ATS respiratory impairment categories, which define an FEV1 down to 60% of predicted as mild obstruction, an FEV1 between 41% and 59% of predicted as moderate obstruction, and an FEV1 of 40% or less of predicted as severe obstruction, as was done in the 2000 ACOEM statement.1,17 These cut points from the 1986 ATS statement are consistent with those used in OSHA's cotton dust standard12 and they largely overlap those employed in the sixth edition of the AMA guides.18 However, these cut points are lower than the sample method presented by the ATS/ERS in 2005.5
In the absence of airways obstruction (FEV1/FVC ≥ LLN), Step 3 of Fig. 13 evaluates the FVC, to determine whether restrictive impairment may exist. If FVC is less than LLN, restrictive impairment is possible, and it may need to be confirmed using additional tests of pulmonary function, such as lung volume measurements. In the presence of airways obstruction (FEV1/FVC < LLN), FVC less than LLN indicates a possible mixed impairment pattern, and its restrictive component may also need to be confirmed by additional PFTs.
In 2005, ATS/ERS recommended grading restrictive impairment, as well as airways obstruction, using the FEV1% of predicted.5 From a practical standpoint, this may be reasonable since both the FVC and FEV1 are reduced as restrictive impairment progresses, and the common technical problems of early termination of maneuvers and zero-flow errors are less likely to impair the accuracy of the FEV1 than the FVC. However, for workers with mixed impairment patterns, grading the restrictive impairment using FEV1% of predicted might slightly overstate the severity of restriction due to the coexisting obstructive reduction of the FEV1.
By relying on the FEV1% of predicted, the ATS/ERS 2005 definitions of restrictive impairment severity now differ significantly from those presented in the AMA guides sixth edition.18 The AMA guides remains closer to the ATS 1986 respiratory impairment definitions, labeling mild restriction as FVC between 60% and 69% of predicted, moderate restriction as FVC between 51% and 59% of predicted, and severe restriction as an FVC between 45% and 50% of predicted.
Forced Expiratory Flow Rates
Because of the wide variability of the FEF25%–75% and the instantaneous flow rates, both within and between healthy subjects, ATS/ERS continues to strongly discourage their use for diagnosing small airway disease in individual patients5,19 or for assessing respiratory impairment. Interpretation of FEF25%–75% and other flow rates is not recommended if the FEV1 and the FEV1/FVC are within the reference range, although the flow rates may be used to confirm the presence of airways obstruction in the presence of a borderline FEV1/FVC.5,19
The American College of Occupational and Environmental Medicine continues to strongly recommend that occupational medicine practitioners follow the ATS/ERS algorithm for separating normal from abnormal test results. Presence of airways obstruction is indicated by an FEV1/FVC below the worker's LLN, and presence of possible restrictive impairment is indicated by an FVC less than LLN. Practitioners need to remember that an FEV1/FVC that is barely abnormal, in the presence of both FEV1 and FVC more than 100% of predicted, may indicate a normal physiologic variant pattern in healthy nonsmoking populations, such as emergency responders. However, if such healthy workers are exposed to known respiratory hazards, it is recommended that the possibility of airways obstruction be also considered when an abnormal FEV1/FVC is observed.
The goal of evaluating change over time in medical surveillance programs is to identify pulmonary function that may be declining faster than expected over time. Confirmation of an excessive decline then needs to trigger referral for further medical evaluation to determine whether possible injury or harm has been caused by workplace or other exposures. Finding excessive declines also needs to prompt interventions such as removal from hazardous exposures, smoking cessation, initiation of appropriate respiratory protection, or identification of new hazardous exposures. Large short-term declines have served as important early indicators of respiratory disease in some food flavorings manufacturing workers.31–36 In contrast, small short-term lung function declines are variable,37–40 though long-term excessive loss of pulmonary function may predict increased respiratory disease and mortality.41,42
Longitudinal evaluation is particularly important for many healthy workers whose baseline pulmonary function is above average (>100% predicted). Since such workers start off so far above average, they can experience significant lung function decline without falling below the cross-sectional LLN and being labeled “abnormal” on any single PFT. If high-quality serial spirometry tests are recorded over an adequate length of time, longitudinal evaluation may reveal deterioration earlier than repeated traditional cross-sectional evaluations.2,9,43 Factors other than workplace exposures that influence lung function change over time include technical aspects of test performance, weight gain,44–46 other lung conditions (eg, asthma), and personal habits (eg, smoking). The American College of Occupational and Environmental Medicine has discussed some of these issues in detail.2
The importance of conducting valid tests, maintaining high technical quality, and using spirometers that exceed minimum standards for accuracy and precision cannot be overstated when evaluating change over time.2,11 As discussed earlier, both over- and under-recording of results can be caused by errors in technique, flawed spirometer calibration, or sensor problems that occur during the subject test. Such problems can bias the estimates of change, for example, making declines appear “excessive” if a baseline is falsely elevated, or conversely, masking a true loss if the baseline is under-recorded or follow-up results are over-recorded.
Of particular concern in the occupational setting is the variation in technical quality and testing protocols that occurs when occupational health vendors, spirometers, or both are changed frequently. Such inconsistency makes it difficult to accurately measure a worker's change in pulmonary function over time. On-going quality assurance (QA) reviews of spirometry test results are critical in such situations. As an adjunct to a QA program, public domain software, Spirola (Centers for Disease Control and Prevention/NIOSH, Atlanta, GA),47 is available to help users examine the variability of their serial pulmonary function data, which is often increased by poor technical quality. However, users need to remember that some respiratory diseases also cause increased variability over time, and that technical errors, which are consistent over time may bias spirometry results without increasing their variability.
Occupational medicine practitioners need to determine whether monitoring decline in pulmonary function has been shown to be effective in screening for a particular outcome disease of interest. There is general consensus that early detection of accelerated pulmonary function decline in flavoring and microwave-popcorn manufacturing workers should trigger comprehensive medical evaluation and workplace interventions.11 However, the effectiveness of monitoring longitudinal pulmonary function is less clearly demonstrated in other occupational settings. Therefore, practitioners need to regard the finding of a possible excessive decline as an opportunity to further assess an individual's health, and not use it as a label or to stigmatize a worker. Such inappropriate labeling may negatively impact the worker's employment status while not gaining him/her any improvement in respiratory health.
Clinicians have accumulated many decades of experience in the traditional evaluation of patient spirometry test results relative to the cross-sectional reference range. In contrast, relatively little evaluation of lung function loss over time has occurred. Since 1991, ATS has recommended that a year-to-year change in healthy individuals needs to exceed 15% before it is considered as clinically meaningful, so that “changes” in lung function are not likely to be caused only by measurement variability.5,19 In 1995, NIOSH adopted this definition48 and recommended that an age-adjusted percent decline from baseline be calculated, with medical referral if the FEV1 declined by 15% or more after taking aging effects into account.
To provide some guidance for occupational medicine practitioners, ACOEM adopted these definitions and approaches when it defined its longitudinal normal limit in 2004.2 A worker's longitudinal normal limit is derived specifically from his/her baseline results, and corresponds to a 15% drop from the baseline, after allowing for expected average loss due to aging. Falling below the longitudinal normal limit means that the worker has lost more lung function than was expected due to aging and measurement variability. After a low value is confirmed, medical referral is recommended. In 2007, the California Department of Public Health recommended using the cutoff of a 15% decline to trigger a medical evaluation for flavor manufacturing workers.11 This cutoff was chosen to avoid the false positives that are likely to occur when pulmonary function is measured in many non-standardized, real-world clinic situations.
And finally, NIOSH researchers have been working to expand the practice of longitudinal evaluation of pulmonary function, developing public domain software, Spirola, for this purpose, and analyzing several large standardized databases, to determine how tightly the longitudinal lower limit of normal might be set when high quality test results are evaluated over time.8,47 The National Institute for Occupational Safety and Health estimates of abnormal longitudinal change, obtained from good quality results for normal healthy workers, are generally smaller than the 15% recommended by ACOEM, ATS/ERS, and the 1995 NIOSH criteria document, and so a range of cutoffs for excessive pulmonary function declines may emerge as clinical experience with these measurements accumulates. For now, the recommendation of a NIOSH Health Hazard Evaluation may be generally appropriate for longitudinal evaluations of pulmonary function: “... workers with FEV1 falls of about 10% to 15% (depending on spirometry quality) [emphasis added] from baseline should be medically evaluated.”49
The American College of Occupational and Environmental Medicine strongly recommends that the interpretation of pulmonary function change over time requires both an evaluation of the technical quality of the tests and an adequate length of follow-up. When high-quality spirometry testing is in place, ACOEM continues to recommend medical referral for workers whose FEV1 losses exceed 15%, after allowing for the expected loss due to aging. Smaller declines of 10% to 15%, after allowing for the expected loss due to aging, may be important when the relationship between longitudinal results and the endpoint disease is clear. These smaller declines must first be confirmed, and then, if the technical quality of the pulmonary function measurement is adequate, acted upon.
Pre- to Postbronchodilator Changes in Pulmonary Function
There is general agreement that a pre- to postbronchodilator increase in FEV1 (and/or FVC) needs to be at least 12% of the initial value and 0.2 L to be called significant, that is, a bronchodilator response that is suggestive of airways hyperre-activity.5,50–52 Percent change from the initial value is calculated as [(initial value – postbronchodilator value)/initial value] × 100. However, failure to achieve such a response to bronchodilators does not completely exclude the possibility of reversible airways disease, and testing may have to be repeated more than once. Attention focuses first on changes in the FEV1 and then, secondly, on the FVC because changes in the FVC may be produced by varying lengths of expiration recorded before or after the bronchodilator.
The American College of Occupational and Environmental Medicine continues to recommend that a pre- to postbronchodilator increase in FEV1 (and/or FVC) be 12% or more of the initial value and at least 0.2 L to be considered suggestive of reversible obstructive airways disease. The American College of Occupational and Environmental Medicine also concurs with the ATS and the AMA that determinations of permanent impairment need to use a worker's best values for FVC and FEV1, whether recorded before or after bronchodilator administration.
1. Equipment Performance
The American College of Occupational and Environmental Medicine recommends that facilities performing occupational spirometry tests maintain a procedure manual documenting equipment type, spirometer configuration, manufacturer's guidelines, calibration log, service and repair records, personnel training, and standard operating procedures. Such a manual will permit troubleshooting if problems arise with test results.
- Spirometer specifications
- The American College of Occupational and Environmental Medicine recommends that spirometers of all types meet or exceed recommendations made by ATS/ERS 2005 and, eventually, by ISO 26782:
It is also recommended that spirometers which will be used in the occupational setting:
- Performance-based criteria for spirometer operation, including, for example, accuracy, precision, linearity, frequency response, expiratory flow impedance, and other factors;
- Minimum sizes and aspect ratios for real-time displays of flow-volume and volume-time curves and graphs in hard-copy printouts (see the Appendix); and
- Standard electronic spirometer output of results and curves.
Validation testing of spirometers If spirometers are purchased for use in the occupational health setting, ACOEM strongly recommends that:
- Store all information from up to eight maneuvers in a subject test session;
- Permit later editing and deletion of earlier flawed test results;
- Be capable of including all flow-volume and volume-time curves and all test results from at least the three best maneuvers, and preferably from all saved efforts, in the spirometry test report;
- Provide computer-derived technical quality indicators;
- Provide a dedicated routine for verifying spirometer calibration; and
- Save indefinitely a comprehensive electronic record of all calibration and calibration verification results.
Spirometer accuracy checks The American College of Occupational and Environmental Medicine recommends that:
- The manufacturer needs to provide written verification that the spirometer successfully passed its validation testing, preferably conducted by an independent testing laboratory, and that the tested spirometer and software version correspond with the model and software version being purchased; and
- The spirometer needs to meet the ATS/ERS recommended minimum real-time display and hardcopy graph sizes for flow-volume and volume-time curves and ISO minimum aspect ratios for these displays, as well as providing a standard spirometer electronic output (see the Appendix).
Avoiding sensor errors during subject tests
- Spirometer accuracy be checked daily when in use, following the steps outlined in this document;
- Tracings and records from these checks be saved indefinitely;
- A log is kept of technical problems found and solved, as well as all changes in protocol, computer software, or equipment; and
- Spirometers purchased for use in the occupational setting have dedicated calibration check routines (as noted earlier).
- Users of flow-type spirometers need to recognize the flawed curves and test results that may be caused by sensor contamination or zero-flow errors (Figs. 2 to 5); and
- Protocols need to be established and used to prevent these errors from occurring and to correct the errors if they do occur. See the text for specific suggestions.
2. Conducting Tests
- Technician training All technicians conducting occupational spirometry tests should successfully complete a NIOSH-approved spirometry course initially, and a NIOSH-approved refresher course every 5 years.
- Conducting the test
Testing goal for a valid test
- Technicians need to explain, demonstrate, and actively coach workers to perform maximal inspirations, hard and fast expiratory blasts, and complete expirations.
- Testing should be conducted standing, positioning a sturdy chair without wheels behind the subject, unless the subject has previously experienced a problem with fainting.
- Record test posture on the spirometry record and use the same posture for all serial tests over time.
- Disposable nose clips are recommended.
- To achieve a valid test, occupational spirometry should attempt to record 3 or more acceptable curves, with FVC and FEV1 repeatability of 0.15 L (150 mL) or less. A poster portraying many unacceptable curves has recently been published by NIOSH.53 See the text for definitions of terms.
- Failure to achieve repeatability is often caused by submaximal inhalations, though very poor repeatability (eg, > 0.50 L) may indicate sensor contami-nation or zero-flow errors.
- Failure to achieve repeatability needs to be taken into account during the interpretation of results.
Quality assurance reviews
- Spirometry test reports need to present results and curves from all acceptable maneuvers to permit technical quality to be fully evaluated.
- The largest FVC and largest FEV1 are interpreted, even if they come from different curves. Note that many currently available spirometers fail to meet this ATS/ERS and OSHA requirement.
- Test reports need to list the source of the reference values used as well as displaying the LLNs for clinician evaluation.
- Default spirometer configurations need to be examined and often adjusted, if possible, to meet these requirements and recommendations.
- The American College of Occupational and Environmental Medicine recommends that facilities performing occupational spirometry tests need to establish on-going programs providing QA reviews of spirograms.
- Reviews need to be conducted at least quarterly, and more often if technicians are inexperienced or if poor technical quality is observed.
- The goal of such reviews is to assure that 80% or more of an occupational health program's spirometry tests are technically acceptable.
- It is recommended that QA reviewers be experienced in recognizing and correcting flawed spirometry test results.
3. Comparing Results With Reference Values
- Reference values
Race-adjustment of predicted values and lower limits of normal
- The American College of Occupational and Environmental Medicine recommends that the NHANES III (Hankinson) reference values be used unless a regulation mandates another specific set of reference values.
- If NHANES III reference values are not available on older spirometers, ACOEM recommends using the Crapo prediction equations, and only using the Knudson 1983 equations if neither NHANES nor Crapo equations are available.
- Use NHANES III race-specific reference values, basing a worker's race/ethnicity on self-report.
- Apply a scaling (“race-adjustment”) factor of 0.88 to white-predicted values and LLNs for FVC and FEV1 to obtain appropriate reference values for Asian workers.
- If NHANES III reference values are not available when testing African American workers, apply a scaling factor of 0.88 to white-predicted values and LLNs for FVC and FEV1, unless other practices are mandated by an applicable regulation.
- The predicted FEV1/FVC and its LLN are not race adjusted.
- To separate normal from abnormal test results, first examine the FEV1/FVC to determine whether obstructive impairment is present, and then evaluate the FVC to determine whether restrictive impairment may exist. The FEV1 is examined if the FEV1/FVC indicates possible obstructive impairment, as shown in Fig. 13.
- All three indices of pulmonary function are considered abnormal if they fall below their fifth percentile LLN. Fixed cutoff points for abnormality such as 80% of the predicted value or an observed FEV1/FVC ratio less than 0.70 should not be used in the occupational health setting.
- An FEV1/FVC that is barely abnormal, in the presence of FEV1 and FVC more than 100% of predicted, may indicate a normal physiologic variant pattern in healthy nonsmokers. However, if such healthy workers are exposed to known respiratory hazards, clinical judgment is needed to evaluate the possibility of early airways obstruction.
4. Evaluating Results Over Time
- Longitudinal interpretation
Pre- to postbronchodilator changes in pulmonary function
- Evaluate technical quality of the spirometry tests and the adequacy of the follow-up period before interpreting change in pulmonary function over time.
- The American College of Occupational and Environmental Medicine recommends that FEV1 losses exceeding 15% since baseline, after allowing for the expected loss due to aging, trigger further medical evaluation when spirometry is of high technical quality.
- The American College of Occupational and Environmental Medicine recommends that a confirmed FEV1 decline of 10% to 15% since baseline, after allowing for the expected loss due to aging, would trigger further medical evaluation, when loss of FEV1 is known to be related to an endpoint disease and test quality is adequate.
- A pre- to postbronchodilator FEV1 or FVC increase of 12% of the initial value and 0.2 L is suggestive of reversible obstructive airways disease.
- Determinations of permanent impairment need to be based on a worker's best values for FVC and FEV1, whether recorded before or after a bronchodilator.
The committee thanks, first and foremost, the many members of the occupational health community who for decades have generously shared their interest, questions, and perspectives on occupational spirometry testing. Second, the committee thanks Drs John Hankinson and Philip Harber for their support and insightful comments during the development of this position statement. This guidance statement was reviewed by ACOEM Council of Scientific Advisors, and approved by ACOEM Board of Directors on January 23, 2010.
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