Reported significant changes in forced vital capacity(FVC), forced expiratory volume in one second (FEV1), mid-expiratory flow (MEF25–75%) and carbon monoxide diffusing capacity (DL,CO) over time
| FVC | FEV1 | MEF25–75% | DL,CO | |
| Within a day | ||||
| Normal subjects | ≥5 | ≥5 | ≥13 | >7% |
| COPD patients | ≥11 | ≥13 | ≥23 | |
| Week to week | ||||
| Normal subjects | ≥11 | ≥12 | ≥21 | >6 units |
| COPD patients | ≥20 | ≥20 | ≥30 | >4 units |
| Year to year | ≥15 | ≥15 | >10% |
The variables are the same as in tables 6⇑ and 8⇑. Results for spirometry are rounded to the nearest integer 25, 128. The within-day DL,CO variability is from a study of diurnal variation in healthy nonsmokers 133. The week-to-week coefficient of repeatability (CR) is given for DL,CO in units of mL·min−1·mmHg−1, as calculated from CRs originally stated in units of mmol·min−1·kPa−1 138. The year-to-year variability of healthy adults is given using a 95% confidence interval 139. CRs from repeatability testing performed in your own laboratory should be substituted for the values in this table. COPD: chronic obstructive pulmonary disease.