ATS Pulmonary Function Laboratory Manual

ATS Pulmonary Function Laboratory Management & Procedure Manual | 3rd Edition

Measurement Precision 1.1. Precision (repeatability) describes the laboratory’s ability to get the same result when testing a biologic control or using another type of control (e.g., known-volume syringe). 1.1.1. Precision standards defining a “repeatable” result for individual pulmonary function tests have been established by the American Thoracic Society (ATS) and European Respiratory Society (ERS) (3–5). They are also included in the specific testing chapters in this manual. 1.1.2. Demonstrating repeatability requires at least the following number of acceptable trials for the specific test(s) for which the precision range is being determined: 1.1.2.1. Dl CO : • ≥ 2 acceptable trials • Repeatability: within 3 ml CO/min/mm Hg of each other, or within 10% of highest value. 1.1.2.2. Functional residual capacity (FRC) using body plethysmograph: • >3 acceptable trials • Repeatability: within 5% (i.e., difference between the highest and lowest acceptable value divided by the mean is < 0.05). 1.1.2.3. Airway resistance (Raw): • >3 acceptable trials • Repeatability: within 10% of the mean (6) 1.1.2.4. Gas dilution FRC (i.e., FRC He , FRC N2 ): • 1 or 2 acceptable trials • Repeatability (if appropriate): within 10% 1.1.2.5. Spirometry: • 3 acceptable trials • Repeatability: FVC within 0.150 L , FEV 1 within 0.150 L; for those with an FVC of ≤ 1.0 L, both these values are 0.100 L. Quality Control Analysis 1. Quality control analysis evaluates an acceptable/repeatable test result versus a standard. Standards can be calibrating syringes, biological controls, or control material(s). 2. In a stable laboratory environment the distribution of the results of the same calibration syringe, biologic control, or control material(s) analyzed a number of times is a Gaussian (normal) distribution. 2.1. In a normal distribution 2.1.1. approximately 65% of the values will be between ±1 SD of the mean 2.1.2. approximately 95% of the values will be between ±2 SD of the mean 2.1.3. approximately 99% of the values will be between ±3 SD of the mean 3. For each quality control parameter you have chosen to use (e.g., spirometer volume with a calibrated syringe, Dl CO measurements on a biologic control, etc.), the laboratory should establish a database of mean values and SD by repeated testing of the standard. This generally requires at least 10–20 measurements on different days. An example of a data reporting form is in Appendix 5.1.

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