A physician associated with my PFT lab has become an investigator for a device study intended for patients with severe COPD. One of the major criteria for patients to be able to enroll in this study is a severely elevated Residual Volume (RV). Patients who have met this criteria at other PFT labs in New England have been referred to this study but when they have been re-tested in my lab their Residual Volumes are coming out lower and almost none of these patient have met this criteria. We have been asked why this is the case because they are now having difficulty finding patients that qualify for the study.
We have not been given access to the original PFT reports for these patients and have not been able to actually compare results on a case by case basis. For this reason we can only offer two possible reasons. First, that my lab may not be using the same reference equations for RV that other labs are. Second, that these patient’s RV’s may have been overestimated at other labs because of errors in testing.
To compare predicted RV’s I was able to find a dozen different reference equations for RV in adult males and females. These equations are mostly for Caucasian populations, but I was also able to find at least one reference equation each for Black, Asian, Indian, Iranian and Brazilian populations as well.