Certified Pulmonary Function Technologist (CPFT) Practice Exam

When performing DLCO testing, how closely must vital capacity (VC) align with the measured VC from spirometry?

1. 75%

2. 80%

3. 85%

4. 90%

The correct answer is: 85%

In the context of DLCO (Diffusing Capacity of the Lung for Carbon Monoxide) testing, the alignment of the measured vital capacity (VC) from DLCO testing with the VC obtained from spirometry is crucial for ensuring the reliability of the test results. A threshold of 85% is considered an appropriate standard for this alignment. When the vital capacity values closely match, it indicates that the lung volumes measured during the DLCO test are consistent with those measured during spirometry. This consistency enhances the validity of the diffusing capacity measurements, as significant discrepancies could suggest either technical errors in the testing or variations in lung function that might affect interpretation. If the measured VC during the DLCO procedure falls below 85% of the VC measured on spirometry, it raises concerns about the accuracy of the DLCO results. Therefore, having the VC align at or above this threshold ensures that the lung's ability to transfer gases is assessed under comparable conditions, thus yielding more reliable clinical information.