FVC Quality Categories
A = At least 3 acceptable curves with one-second plateau or > 15 s duration and repeatable within 150 mL
B = At least 2 acceptable curves with one-second plateau or > 15 s duration and repeatable within 150 mL
C = At least 2 acceptable curves with one-second plateau or > 15 s duration and repeatable within 200 mL
D = At least 2 acceptable curves with one-second plateau or > 15 s duration and repeatable within 250 mL
F = No acceptable curves
FEV1 Quality Categories
A = At least 3 acceptable curves repeatable within 150 mL
B = At least 2 acceptable curves repeatable within 150 mL
C = At least 2 acceptable curves repeatable within 200 mL
D = At least 2 acceptable curves repeatable within 250 mL
F = no acceptable curves
Acceptable Curve Definitions
Free from artefacts
No cough during the first second of exhalation
No glottis closure or abrupt termination that influences the measurement
No early termination or cut-off
Effort that was maximal throughout the maneuver
No obstructed mouthpiece
A good starts: extrapolated volume < 5% of FVC or 150 mL, whichever is greater (FVC and FEV1 grades)
For FVC and FEV1 grades calculations, an acceptable curve's FVC or FEV1 should not differ by more than 300 mL from the largest observed FVC or FEV1, otherwise it is considered unacceptable due to an incomplete inhalation.