Olfaction as a diagnostic instrument - a review of current, and future medical applications

The olfactory sense has evolved to provide environmental and physiological cues through the detection of volatile organic compounds. While historically a clinician's sense of smell was used to assist in diagnosing illness, with some notable exceptions, this has fallen out of favour with the advent of analytical tools. Recently, world events have shown that olfactory methodologies can be highly useful for diagnostic purposes. The emergence of the SARS-CoV-2 virus (causing COVID-19) presented a number of logistical issues with regards to establishing fast and accurate diagnosis-while the idea of detection dogs was proposed at the time, little in the way of routine clinical application was accomplished for this disease. The reasons for this are multifactored, but the use of olfaction as a diagnostic tool can be efficacious, provided appropriate methodological considerations are met. Here, the use of olfaction within a medical diagnostic framework is discussed; with olfactory diagnosis having the potential of very high sensitivity and specificity, but with a low diagnostic cost in terms of expense, time, and patient discomfort. This review will also discuss the ways in which olfactory medical diagnosis can be accomplished using humans, dogs, as well as other animals. Finally, this paper will outline recommendations of how future olfactory diagnostic options can be researched and implemented to ensure best practice.