The following information is from Mason, Murray and Nadel’s Textbook of Respiratory Medicine, 5th ed. 2010. I have abstracted and edited it. I would stress the following:
This is a technically complex test that requires an experienced technician and good laboratory quality control.
The test result should be interpreted in the context of other laboratory, X-ray and clinical information.
There are physiologic causes, other than lung disease that can result in a low diffusion capacity; e.g., heart failure (your ejection fraction of 40 noted) and anemia.
There is a wide range of predicted “normal” values.
A low diffusing capacity, when due to pulmonary disease, can be secondary to disease of the bronchial tubes, the lung substance (emphysema) or the blood vessels. In this regard, the CT Scan and other normal pulmonary function tests are very reassuring, despite the nodules, that are probably of no clinical significance.
I suggest that you not request a second opinion, at this time, but rather that you have a conversation with your Pulmonary specialist, ask if any of the information below might be relevant to your condition and ask him/her for his/her interpretation of the reduced diffusion capacity, in the context of the normal PFT’s, and if any further studies (pulmonary or cardiac) might be warranted. You might also want to ask the pulmonologist and/or the cardiologist if the cardiac catheterization ruled out pulmonary hypertension and, given the thickened pericardium, if it ruled out constrictive pericarditis.
Diffusing capacity is often abnormal in patients with interstitial lung disease, pulmonary vascular disease, and COPD, but can be erroneously low for technical reasons.
The measurement of the single-breath DlCO measurement is more complex than spirometry. It requires a higher level of commitment and expertise for test performance, maintenance, and quality control. Gas analyzer instability is a frequently unrecognized technical source of increased variability. As with all PFTs, the first step in interpreting a DlCO study is to review and comment on test quality and repeatability. The results from two acceptable tests should be within 3 mL CO (STPD)/min/mm Hg of each other and the mean value reported. Adjustments for hemoglobin and carboxyhemoglobin should be reported. The test is judged abnormal if it is below the lower 5th percentile of the reference population.
Physiologic sources of variability may be more difficult to control than technical sources of variability but must be considered when interpreting changes in an individual's DlCO. Reduced hemoglobin (anemia) results in a reduction in DlCO and an adjustment for hemoglobin concentration is important for interpretation. Other physiologic conditions can affect DlCO. Current and former cigarette smokers have small reductions in DlCO compared with never smokers that is proportional to the number of pack-years.
Diffusing capacity interpretation is most clinically useful when it is performed in conjunction with measurements of spirometry and lung volumes. A low DlCO with normal spirometry suggests the presence of pulmonary vascular disease, early interstitial lung disease, anemia (reduced hemoglobin), or elevated carboxyhemoglobin level (usually secondary to cigarette smoking, but can also be secondary to exposure to increased carbon monoxide in the ambient air.) Pulmonary vascular diseases such as idiopathic pulmonary artery hypertension, pulmonary embolism, chronic thromboembolic pulmonary hypertension, and pulmonary vasculitis should be considered in a patient with a significant reduction in DlCO and normal spirometry and lung volumes. Early interstitial lung disease can cause mild to moderate reductions in DlCO before the development of abnormal spirometry and lung volumes. Emphysema with a concomitant restrictive process such as idiopathic pulmonary fibrosis, amiodarone-induced interstitial lung disease, and hypersensitivity pneumonitis has been associated with a reduced DlCO and normal spirometry and lung volumes.
I just wanted to comment that the Pulmonologist didn't think there was anything to worry about even though I had the low DLCO and the "ground glass nodule". I wanted to know regarding that info if I should seek another opinion, perhaps with NJH? Thanks.