Periodontal disease (PD) is one of the most prevalent clinical conditions in dogs, representing a considerable concern in veterinary practice, not only because of its local effect, but also because of its significant systemic impact, which is reflected by its association with other comorbidities such as endocarditis, hepatitis, and chronic kidney disease. Haematological ratios (HR), easily obtained from complete blood counts (CBC), have emerged as promising indicators of systemic inflammation in both human and veterinary medicine. These HR integrate the interaction of different cell lines and provide a more comprehensive view of the inflammatory response compared to isolated counts of the various cell lines. However, their role in canine PD has not yet been widely investigated, and to date there are no studies evaluating their potential as inflammatory biomarkers at different stages of canine PD and in a single dog breed.

Therefore, the objective of this retrospective study was to assess the clinical significance of five HR - neutrophil/lymphocyte ratio (NLR), platelet/lymphocyte ratio (PLR), mean platelet volume/platelet count ratio (MPV/PLT), monocyte/lymphocyte ratio (MLR), and platelet/neutrophil ratio (PNR) - in 80 Portuguese Podengo dogs. The animals were classified according to their PD status: clinically healthy (n = 24), gingivitis (n = 26) and periodontitis (n = 30).

The analysis revealed statistically significant differences in three of the five ratios. NLR was lower in dogs with periodontitis compared to the healthy and gingivitis groups, reflecting the increased role of lymphocytes in the chronic phase of the disease, characteristic of an adaptive immune response. The PLR was significantly reduced in both gingivitis and periodontitis compared to controls, which once again reflects the lymphocyte predominance that occurs with disease progression. The PNR was lower in gingivitis than in healthy dogs, a result that may be a direct consequence of the increase in the number of neutrophils characteristic of acute inflammatory responses. In contrast, MPV/PLT and MLR showed no significant differences between groups, rendering them unsuitable as inflammatory biomarkers of canine PD.

Analysis of the receiver operating characteristic (ROC) curve indicated weak discriminatory power for all indices, with areas under the curve (AUC) between 0.5 and 0.7. Nevertheless, PNR performed best in distinguishing between gingivitis and healthy individuals (AUC = 0.692). However, this weak discriminatory power makes it impossible to use these HR exclusively for diagnosing the different stages of canine PD, and their application should be complemented with a detailed stomatological-dental examination. In conclusion, this study demonstrates that PD induces measurable systemic changes in HR, particularly NLR, PLR, and PNR. Although their diagnostic accuracy is limited, these indices are simple, inexpensive, and non-invasive tools that can complement clinical evaluation and dental examination. In the future, studies involving larger samples and substaging periodontitis should be developed in order to understand the possible evolution that these HR may present following periodontal treatment.