• Clinical pathology;
  • Decision support;
  • Evidence-based medicine;
  • Oncology diagnosis;
  • Uncertainty

Background: Cytology often is used to obtain a diagnosis, such as that of malignant neoplasia. When a diagnosis is uncertain, pathologists often express probability using qualitative terms, such as “probable,” that have imprecise meanings.

Hypothesis: Terms expressing probability are interpreted variably by veterinary practitioners and affect decisions regarding treatment and euthanasia.

Animals: None.

Methods: An online survey of members of the Veterinary Information Network was conducted. Veterinarians were asked to assign percentage probabilities to 18 modifiers of a diagnosis of lymphoma. They also were asked to select their most likely clinical action based on a diagnosis of lymphoma qualified one of 4 modifiers. Results were analyzed using descriptive and nonparametric methods. Percentage probabilities were analyzed by ANOVA after variance stabilization.

Results: For 871 valid surveys, probabilities assigned to the 18 modifiers overlapped substantially, with medians (interquartile range) of 50% (50–70%) for “possible,” 66% (66–85%) for “probable,” and 70% (70–90%) for “consistent with.” More (P < .001) veterinarians (50.4%) chose to initiate treatment with a diagnosis of “consistent with lymphoma” as compared with “probable” (14.6%) or “possible” (1.6%) lymphoma. For clients considering euthanasia if the diagnosis was cancer, more (P < .001) veterinarians recommended euthanasia with a diagnosis of “consistent with lymphoma” (62.5%) as compared with “probable” (35.3%), or “possible” (2.0%) lymphoma.

Conclusions and Clinical Importance: Probability expressions are interpreted variably yet have a major impact on clinical decision-making, including the decision to recommend euthanasia. Standardized terminology could improve decision-making and enhance clinical outcome.