Anatomy of a Vet Visit (part three)

When the source of a patient’s problem isn’t clear after our time in the exam room is complete, diagnostic testing is usually needed. This requires analysis of a lab sample from the patient, such as blood or urine, or the capture of images using something like an x-ray or MRI.

Diagnostic testing is the only route to a solution for most of the problems seen at any medical facility, and a suitable foundation for treatment can usually be found after one or two tests. On the other hand, we must understand that appropriate testing doesn’t provide a guaranteed diagnosis, and that agreeing to these procedures is not the outright purchase of an answer. That’s because every health test has its limitations. Some tests have a very wide “gray zone” between the positive and negative, where the results can’t be easily categorized as one or the other. Some tests are only reliable when they come up negative (because they provide too many false positives), and others are only reliable when they are positive (because they produce too many false negatives). Look at this like asking a toddler whether she pilfered a cookie from the kitchen. If the answer is “yes,” then that’s virtually certain to be true. If the answer is “no,” you will probably have to employ a second test, such as a rigorous crumb check or follow-up interrogation. In the case of stolen cookies, there are just way too many false negatives.

It sometimes happens that a particular test is necessary, but functionally impossible. Some procedures will be deemed hazardous and unwise, because collection of the appropriate samples would be too invasive for an already fragile patient. Uncovering your pet’s exact diagnosis at the cost of his survival isn’t a smart bargain. Many of the more advanced tests can only be conducted at a few distant locations. Some take so long to conduct that the patient’s fate is already sealed by the time the results come in. Some tests are just too expensive for the average person’s finances to withstand. For many conditions, a test hasn’t even been invented.

I’m very often asked whether a blood test will reveal any cancer. Sadly, they almost never do (meaning that this test gives way too many false negatives when used to investigate a possible cancer). Any type of cell in the body can give rise to a cancer, and the only one visible on a blood test would be a cancer of the blood. It’s true that blood tests are used to measure cancer markers in human beings, but that type of highly specialized analysis is largely unavailable for animal patients.

The lab work and imaging phase of your vet visit is the final part in our series, but in a way it is just the beginning. Diagnostic testing is much like a puzzle with a handful of pieces missing, but we’ll work together using the other elements of your vet visit to get a glimpse of the big picture.

Dr. M.S. Regan