Spirometry Repeatability Criteria (ATS/ERS)

Acceptable Repeatability Thresholds

• The two largest forced vital capacity (FVC) values must differ by ≤ 0.150 L and the two largest forced expiratory volume in 1 s (FEV₁) values must differ by ≤ 0.150 L; when a patient’s FVC is ≤ 1.0 L, both thresholds are reduced to ≤ 0.100 L. 1

Minimum Number of Acceptable Maneuvers

• At least three acceptable maneuvers (i.e., meeting all within‑maneuver quality criteria) are required before assessing repeatability. 1, 2
• If repeatability is not achieved after three maneuvers, additional trials should be performed, up to a maximum of eight maneuvers (optional stopping point). 1, 3, 4

Selection of Maneuvers for Repeatability Assessment

• Only acceptable maneuvers—those without start‑of‑test errors or coughs—are used to evaluate repeatability; such erroneous maneuvers must be discarded. 1, 2, 5
• Maneuvers that terminate early or include a Valsalva effort may still be considered when selecting the largest FVC and FEV₁ values. 1, 2, 5

Stopping Rules for the Test Session

• The session may be concluded when both repeatability criteria are met (FVC and FEV₁ within the specified thresholds). 1
• Alternatively, testing may stop after eight maneuvers have been performed, or when the patient is unable or should not continue. 6

Patient Fatigue and Variability

• Large variability among trials is frequently caused by incomplete inhalations rather than insufficient effort. 1, 2
• Providing a brief rest period between maneuvers can improve repeatability. 1, 2
• After several forced expiratory attempts, fatigue may reduce performance, making further maneuvers of limited value. 3, 4, 6

Safety Consideration

• Testing must be terminated immediately if a progressive decline in FEV₁ or FVC results in a cumulative drop exceeding 20 % of the initial value, to protect patient safety. 3, 4, 6

Clinical Interpretation Caveats

• The repeatability criteria are minimum requirements for determining when additional maneuvers are needed; they should not be used to exclude results from clinical reports or to disqualify subjects from research studies. Poor repeatability should be documented but the best‑available results must still be reported. 1, 2, 5

Result Selection After Repeatability Assessment

• The largest FVC value is selected from all acceptable curves, regardless of which curve it originates from. 3, 4, 5, 6
• The largest FEV₁ value is similarly selected from all acceptable curves. 3, 4, 5, 6
• The selected FVC and FEV₁ do not need to come from the same curve. 3, 4, 5, 6
• Volume‑time or flow‑volume curves from at least the three best FVC maneuvers should be retained for review. 1, 2