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Scientific evidence on medical detection dogs

A dog’s sense of smell can detect stable concentration thresholds of 1–2 parts per trillion ^[1], this is comparable to detecting a teaspoon of sugar in two Olympic sized swimming pools. Apart from having more scent receptors in their nose (300 million compared to 5 million in humans), dogs use a larger proportion of their brain to analyse scent and can, therefore, distinguish much more details (see also A Dogs Nose, for more information).

Many industries make use of this sensitive sense of smell by training dogs to detect drugs, explosives, money or food, track missing persons or find specific bird species. The first scientific publication on a dog detecting a disease was reported in 1989 by Williams and colleagues (The Lancet, 1989) ^[2]. This and further anecdotal and published case reports prompted investigations into establishing what odour the dogs can smell as well as setting up diagnostic studies to determine the accuracy and clinical potential of dogs detecting diseases.

While it is still unclear what exact markers dogs identify, it has now been established that changes in the cell’s metabolism due to a variety of diseases leads to the release of volatile organic compounds (VOC) that are distinct from VOC released by healthy cells ^[3]. Medical detection dogs can be trained to distinguish these VOCs in urine, breath and tissue samples of patients with the disease (e.g. cancer) from samples of healthy individuals.

The first robust and successful clinical investigation into the training of dogs to detect cancers was conducted by Cornu and colleagues in 2011 ^[4]. The team trained a Belgian Malinois shepherd to detect prostate cancer in urine samples from patients and reported a sensitivity and specificity of 91% in a double-blind, randomised diagnostic trial comprising 66 samples. Since then, similar promising results have been published for a variety of cancer types, that included a larger and more diverse patient population. A few examples are:

• a Japanese study reporting the successful detection of colorectal cancer in faecal and breath samples (sensitivity 97%, specificity 99%) ^[5],
• a series of Swedish studies reporting the successful detection of ovarian cancer in tissue and blood samples (sensitivity 97% specificity 99%) ^[6–8] and
• a German study showing the successful detection of lung cancer in breath samples (sensitivity 71% specificity 93%) ^[9].

Apart from detecting cancer, medical detection dogs have also been trained to detect other diseases, such as detecting bacteria causing urinary tract infection in urine samples ^[10], and research has just started to train dogs to detect Parkinson’s disease from skin swabs.

References:

_{1. Walker DB, Walker JC, Cavnar PJ, Taylor JL, Pickel DH, Hall SB, et al. Naturalistic quantification of canine olfactory sensitivity. Appl Anim Behav Sci. 2006 May 1;97(2–4):241–54.}

_{2. Williams H, Pembroke A. Sniffer dogs in the melanoma clinic? Lancet. 1989 Apr 1;333(8640):734.}

_{3. Filipiak W, Mochalski P, Filipiak A, Ager C, Cumeras R, Davis CE, et al. A Compendium of Volatile Organic Compounds (VOCs) Released By Human Cell Lines. Curr Med Chem. 2016;23(20):2112–31.}

_{4. Cornu J-N, Cancel-Tassin G, Ondet V, Girardet C, Cussenot O. Olfactory Detection of Prostate Cancer by Dogs Sniffing Urine: A Step Forward in Early Diagnosis. Eur Urol. 2011 Feb 1;59(2):197–201.}

_{5. Sonoda H, Kohnoe S, Yamazato T, Satoh Y, Morizono G, Shikata K, et al. Colorectal cancer screening with odour material by canine scent detection. Gut. 2011 Jun 1;60(6):814–9.}

_{6. Horvath G, Järverud G af K, Järverud S, Horváth I. Human Ovarian Carcinomas Detected by Specific Odor. Integr Cancer Ther. 2008 Jun 27;7(2):76–80.}

_{7. Horvath G, Andersson H, Paulsson G. Characteristic odour in the blood reveals ovarian carcinoma. BMC Cancer. 2010 Dec 24;10(1):643.}

_{8. Horvath G, Andersson H, Nemes S. Cancer odour in the blood of ovarian cancer patients: a retrospective study of detection by dogs during treatment, 3 and 6onths afterwards. BMC Cancer. 2013 Dec 26;13(1):396.}

_{9. Ehmann R, Boedeker E, Friedrich U, Sagert J, Dippon J, Friedel G, et al. Canine scent detection in the diagnosis of lung cancer: revisiting a puzzling phenomenon. Eur Respir J. 2012 Mar 1;39(3):669–76.}

_{10. Maurer M, McCulloch M, Willey AM, Hirsch W, Dewey D. Detection of Bacteriuria by Canine Olfaction. Open forum Infect Dis. 2016 Mar;3(2):ofw051.}