Thymidine Kinase Type 1 and C‐Reactive Protein Concentrations in Dogs with Spontaneously Occurring Cancer

Background Serum thymidine kinase type 1 ( TK 1) and canine C‐Reactive Protein ( cCRP ) might be useful in detecting dogs with cancer. Algorithms combining biomarkers are sometimes more accurate than results of individual tests. Objectives The aim of this study was to compare serum TK 1 and cCRP and Neoplasia Index ( NI ) in healthy and tumor‐bearing dogs. Animals Client‐owned dogs with (n = 253) and without (n = 156) cancer. Methods Retrospective case–control study. Dogs with cancer were identified after submission of samples for commercial assay and case details were retrospectively collected. Healthy dogs (control) were identified through breed groups and health status was confirmed by health questionnaire for a minimum of 6 months. Serum TK 1 activity was measured using a quantitative chemiluminescent assay and serum cCRP was measured using a quantitative ELISA assay. Results TK 1 activity in the cancer (n = 253) and control group (n = 156) were 7.0 μ/L (median, range <0.5 to >100) and 1.8 μ/L (median, range 0.4 to 55.3), respectively ( P  < .001). cCRP concentrations in the cancer and control group were 6.0 mg/L (median, range <0.5 to >50) and 1.6 mg/L (median, range 0.09 to >50), respectively ( P  < .001). The NI in the cancer and control group were 6.4 (median, range 0–9.9) and 0.9 (median, range 0–7.6), respectively ( P  < .001). ROC AUC s of the NI and TK 1 for all cancers were greater than 0.8, highest for lymphoma and histiocytic sarcoma. Conclusions and Clinical Importance Increased concentrations of TK 1 and cCRP , when present in dogs with cancer, might be useful in confirming a diagnosis and monitoring response to treatment.