Smelling the diagnosis: a review on the use of scent in diagnosing disease.

For centuries, our sense of smell has been used as a diagnostic tool in the practice of medicine, be it for recognising gas gangrene on the battle field or diabetic ketoacidosis in the emergency room. In recent decades, many scent detection studies have been performed with human, animal and electronic noses. The ability of humans to diagnose disease by smelling has only rarely been the subject of quantitative studies. Scent detection by animals, on the other hand, has been addressed in several diagnostic studies, which all suggest similar or even superior accuracy compared with standard diagnostic methods. Examples include, amongst many others, the use of dogs for the detection of lung cancer in breath samples, or rats for Mycobacterium tuberculosis detection in sputum. Studies using different types of electronic noses in conditions such as pulmonary disease and cancer have also shown promising results with high overall sensitivity and specificity. However, results of different types of noses are not easily generalisable and independent confirmation studies are generally lacking, which should be a focus for future research. In conclusion, scent detection by animals and electronic noses holds promise for the future and should receive higher priority in terms of research effort and funding.