Canine olfaction as a disease detection technology: A systematic review

Capitalizing on canine olfactory capacity is a promising strategy for detecting and diagnosing human, animal, and plant diseases. The purpose of this review was to assess the extent of current research in canine disease detection and to identify factors impacting detection success. In this systematic review and meta-analysis, multiple databases were searched for studies in which dogs were trained to detect diseases or health conditions for both plants and animals. Following PRISMA guidelines, 2109 non-duplicate studies were screened and 58 relevant studies identified. Most studies (n = 33, 57%) took place in Europe. Across all studies, 192 unique detection dogs were tested. The most numerous breed was Labrador Retrievers (n = 27, 14%). The median number of dogs per study was 2 (range: 1–20). To analyze experimental design and results, studies including multiple test paradigms were divided into sub-studies (n = 105). Lung cancer (n = 11, 22%) and prostate cancer (n = 14, 13%) were the most frequently studied conditions. Urine (n = 27, 26%) and breath (n = 15, 14%) were the most common sample materials. In 86% of sub-studies (n = 90), dogs were presented with sets of samples and 72% (n = 76) reported a constant number of samples per trial. The median number of samples per trial was 6 (range: 2–100). Of the sub-studies reporting a fixed number of positive samples (range: 1–10; n = 65), 91% (n = 59) presented one positive sample per trial. A plurality of sub-studies (n = 47, 45%) presented samples in a lineup. Sensitivity (median: 0.90; range: 0.17–1.0; n = 90) and specificity (median: 0.96; range: 0.08–1.0; n = 81) were the predominant measures of detection success. In some cases, study design may have influenced results. There was a positive relationship between specificity and the likelihood of a true negative response based on the number of samples per trial, and specificity was higher in studies that did not include a double blinded test than those that did. Dogs appear to have the capacity to detect disease via olfaction; yet the nascent nature of this discipline yields inconsistency in methodology and reporting.