"Although the pathophysiological significance of these lipid-laden macrophages and their relation to the cause of this syndrome are not yet known, we posit that they may be a useful marker of this disease.3-5 Further work is needed to characterize the sensitivity and specificity of lipid-laden macrophages for vaping-related lung injury, and at this stage they cannot be used to confirm or exclude this syndrome. However, when vaping-related lung injury is suspected and infectious causes have been excluded, the presence of lipid-laden macrophages in BAL fluid may suggest vaping-related lung injury as a provisional diagnosis."There, we outlined the two questions about their significance: 1.) any relation to the pathogenesis of the syndrome; and 2.) whether, after characterizing their sensitivity and specificity, they can be used in diagnosis. I am not a lung biologist, so I will ignore the first question and focus on the second, where I actually do know a thing or two.
We still do not know the sensitivity or specificity of LLMs for VALI, but we can make some wagers based on what we do know. First, regarding sensitivity. In our ongoing registry at the University of Utah, we have over 30 patients with "confirmed" VALI (if you dont' have a gold standard, how do you "confirm" anything?), and to date all but one patient had LLMs in excess of 20% on BAL. For the first several months we bronched everybody. So, in terms of BAL and LLMs, I'm guessing we have the most extensive and consistent experience. Our sensitivity therefore is over 95%. In the Layden et al WI/IL series in NEJM, there were 7 BAL samples and all 7 had "lipid Layden macrophages" (that was a pun). In another Utah series, Blagev et al reported that 8 of 9 samples tested showed LLMs. Combining those data (ours are not yet published, but soon will be) we can state the following: "Given the presence of VALI, the probability of LLM on Oil Red O staining (OROS) is 96%." You may recognize that as a statement of sensitivity. It is unusual to not find LLMs on OROS of BAL fluid in cases of VALI, and because of that, their absence makes the case atypical, just as does the absence of THC vaping. Some may go so far as to say their absence calls into question the diagnosis, and I am among them. But don't read between the lines. I did not say that bronchoscopy is indicated to look for them. I simply said that their absence makes the case atypical and calls it into question.
