Testing for lipid-laden macrophages in bronchoalveolar lavage fluid to diagnose vaping-associated pulmonary injury. Are we there yet?

Vaping-associated pulmonary injury (VAPI) is a severe respiratory disorder associated with the inhalation of nicotine, tetrahydrocannabinol, cannabidiol, or other active substances through a personal vaporizer ("vaping"). Within 2 months after its description, the disease has reached epidemic proportion, affecting over 2000 people and resulting in a number of fatalities. The substance(s) responsible for the lung injury are still unknown, and the pathophysiology of the disease is still incompletely understood. The manifestations of the disease are protean, and the insidiously starting respiratory, gastrointestinal, and constitutional symptoms may initially resemble a viral flu-like illness. The disease may increase in severity, requiring hospitalization, and in more severe cases, mechanical ventilation. The diagnosis of VAPI currently relies on the identification of pulmonary infiltrates on imaging studies in patients who have used vaping products, after excluding infections and other plausible alternative diagnoses. Because VAPI is currently a diagnosis of exclusion, some authors have suggested the use of lipid-laden macrophages (LLM) as a diagnostic test to confirm the disease. We review the current state of the knowledge about the pathologic basis of VAPI, and the literature on the analytic performance of the LLM test to better understand the potential utility of this test in the diagnosis of VAPI. Our review finds little evidence to suggest the use of LLM in the diagnosis of VAPI, since its underlying pathology is acute lung injury, which is unrelated to LLM, and the frequency of their detection varies greatly in different reported series.