Beyond Individual Acute Phase Protein Assessments: Introducing the Acute Phase Index (API) as a Prognostic Indicator in Dogs with Malignant Neoplasia

Acute phase proteins (APPs) are part of the innate immune response, changing during inflammation. An Acute Phase Index (API) is a calculated value that combines multiple APPs. In human medicine, the introduction of APIs has improved outcome monitoring. In veterinary medicine, APIs have been evaluated in livestock and dogs with Leishmaniasis. This study aimed to calculate an API and evaluate its significance in cancer-bearing dogs. Sera were collected from 55 dogs, which were classified by neoplastic category and survival times (> or < than 30 and 90 days). For 32 dogs, multiple samples were available. The API included C-Reactive Protein (CRP) and haptoglobin as positive APPs, and albumin and Paraoxonase-1 (PON-1) as negative APPs. An alternative API excluding PON-1 was calculated. PON-1 levels were lower in round-cell tumors, suggesting increased oxidative stress. Moreover, API increased and PON-1 activity decreased in the last sample in dogs that died before the end of the study. Dogs with shorter survival times showed increased APIs and CRP levels. APIs with and without PON-1 greater than 0.049 and 0.202 at the first sampling were associated with a 3.7- and 4.4-fold higher probability of death, respectively. These results suggest a potential prognostic value of API in dogs with neoplasia.