What are considered acceptable spirometry results in pulmonary function testing?

Updated: May 14, 2020
  • Author: Kevin McCarthy, RPFT; Chief Editor: Nader Kamangar, MD, FACP, FCCP, FCCM  more...
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Characteristics of acceptable spirometry efforts are as follows:

  • The patient is vigorously coached to inspire rapidly to full inflation.

  • The patient shows minimal hesitation at the start of the forced expiration (extrapolated volume < 5% of FVC or 0.10 L, whichever is larger).

  • The patients shows an explosive start of the forced exhalation (rise time to peak flow no greater than 0.150 s). Rise time to peak flow is not available on all spirometers. If it not available, it is not part of the assessment of the acceptability of the start of the forced exhalation.

  • The patient shows no evidence of cough or artifact in the first second of forced exhalation.

  • The results meets one of three criteria that define a valid end-of-forced exhalation: (1) smooth curvilinear rise of the volume-time tracing to a plateau (plateau defined as < 0.025 L volume change in the last 1 s of expiration) of at least 1 second's duration; (2) if a forced test fails to exhibit an expiratory plateau, a forced expiratory time of 15 seconds; or (3) the FVC is within the repeatability tolerance of or is greater than the largest prior observed FVC.

  • Upon completing the forced exhalation, the patient is coached to rapidly (> 2 L/s flow) inhale to full inflation upon completing the forced exhalation providing a value for forced inspiratory vital capacity (FIVC). The maximum FIVC can be no more than 0.100 L or 5% of the FVC larger than the FVC (whichever is greater). If the maximum FIVC is more than 0.100 L or 5% of the FVC larger than the FVC, that effort is not acceptable and cannot be used for reporting of any parameters.

  • Repeatability of the largest FVC and FEV1 within 0.150 L (within 0.100 L if age < 6 y) is demonstrated in at least two efforts.

Example of an acceptable spirometry testing sessio Example of an acceptable spirometry testing session showing evidence 3 efforts that show evidence of an explosive start of forced exhalation that continues until empty and good repeatability of forced vital capacity (FVC) and forced expiratory volume in the first second of the forceful exhalation (FEV1), which usually indicates all efforts started from full inflation.

Comprehensive treatment of technical acceptability of spirometry test results is beyond the scope of this review. Readers are directed to Spirometry Quality Assurance: Common Errors and Their Impact on Test Results. A booklet can also be obtained from the Department of Health and Human Services. It provides examples of common spirometry performance errors and their impact on test results.

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