Doctor Debate: Wellness testing—good medicine or not?
Be sure to read the other side of this debate, Doctor Debate: Wellness testing--More important than ever! by Dr. Fred Metzger.
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Although the ability to do wellness testing has been around for years, it has only been recently that practitioners have emphasized its role in veterinary medicine. I think there are four reasons for this.
First, wellness testing has financial rewards. Over the years, veterinarians have wrestled with innovative ways of increasing their practice revenue. Wellness testing accomplishes this. Not only can wellness testing increase the utilization of other testing modalities in a practice, it also helps reduce the burden of vaccines for practice profit. It is important for veterinary practices to be financially healthy, but the way we achieve this should not supplant good medicine and should be in the best interest of our patients.
Second, veterinarians often do wellness testing out of a need to protect themselves against lawsuits—so-called defensive medicine. Some veterinarians think it's always a good thing to look for things to be wrong. While many clients also demand routine tests, they are often bolstered by advertisements, veterinary information online, and veterinarians. To some extent, veterinarians have taught their clients to demand these things. And as a profession we've systematically exaggerated the benefits of early diagnosis, which doesn't always improve survival, and, at the same time, we don't always tell our clients there might be downsides to testing.
Third, and most important, is that wellness testing "screens" for disease and, therefore, is good medicine. If we are using the term wellness testing interchangeably with screening, then we need to examine the statistical merits of doing so. The optimal screening tests should be cost-effective, easy to perform, and have high sensitivity (correctly detect most patients with a disease) and specificity (correctly identify most patients that do not have a disease). It is also important to realize that normal test values are usually arbitrarily defined as those occurring within two standard deviations from the mean, thereby ensuring that 5% of healthy pets that have a single screening test will have an abnormal result. As more tests are ordered, the likelihood of a false positive result increases. Therefore, a screening panel containing 20 independent tests in a patient with no disease will yield at least one abnormal result 64% of the time.
Then there is the lead-time bias phenomenon.1 This bias refers to a spurious increase in longevity associated with screening. In other words, the screening test could discover a disease before the patient feels ill, but it does not extend the patient's life. This early detection can artificially inflate survival time by moving up the diagnosis date, making the test appear to be useful even though mortality doesn't change.
And what about the scientific evidence in support of wellness testing being a good disease screening tool? In human medicine, the literature is replete with research showing the flaws with wellness testing.2-5 But in veterinary medicine there is a lack of evidence-based research showing that patients benefit from wellness testing. Recently, two studies in veterinary medicine addressed the issues of wellness testing. Both studies looked at preanesthetic testing and whether the test results affected the way we anesthetize patients. The first study, out of Germany, concluded, "The changes revealed by preoperative screening were usually of little clinical relevance and did not prompt major changes to the anesthetic technique."6 The second study, out of South Africa, concluded that 1) screening of geriatric patients is important and that subclinical disease could be present in nearly 30% of these patients, and 2) the value of preanesthetic screening in veterinary anesthesia still needs to be evaluated in terms of appropriate outcome variables.7 So based on two studies, at least one type of wellness testing (preanesthetic) may not be justified.