In veterinary medicine, as in other medical fields, diagnostic tests are essential for guiding treatment and predicting outcomes for various diseases. Both infectious and non-infectious diseases can be diagnosed by detecting the causative agent, clinical signs, pathological changes, biochemical changes, or evidence of past or present exposure to an agent (such as antibodies).
Many of the tests we use detect antibodies, but this raises the question: are the antibodies causing the current clinical signs, or are they from a past infection? Alternatively, could the reaction be a cross-reaction to another agent?
Often, we don't consider what specific information a test will provide, instead basing our recommendations on the prevalence of the disease in your practice area. This concept is known in epidemiology as the pre-test probability of the disease. Disease prevalence varies by region and differs between healthy and sick animals.
For healthy animals, we often screen groups to determine exposure or rule out disease, essentially proving they are healthy. In these cases, we prefer highly sensitive tests to minimize false negatives, making us more confident in a negative result. For sick animals, we want tests that confirm the animal is truly ill (rule-in disease). Therefore, we prefer highly specific tests to reduce false positives, increasing our confidence in a positive result.
These examples were compiled by Dr. William Saville, an Emeritus Assistant Professor and Extension Epidemiologist in the Department of Veterinary Preventive Medicine. Collaborators included Dr. William P. Shulaw, beef cattle and sheep Extension Veterinarian and Dr. Alecia Larew Naugle.
Raw milk, which has not been pasteurized or homogenized, is gaining popularity among those who prefer natural and farm-sourced foods. It is important to be aware of the potential risks associated with its consumption.