Evidence-Based Approach to Medicine Improves Patient Care

That recommendation to try lowering your cholesterol level with drugs is an example of evidence-based medicine. The guidelines were changed based on the findings of five clinical trials that tested the results of cholesterol-lowering drugs in higher risk patients.

Another example of a laboratory test that has evidence-based guidelines delineating its correct use is the test for hemoglobin A1c, or glycosylated hemoglobin, which is used in diabetes management. By measuring glucose bound to hemoglobin, the test gives a picture of the average amount of glucose in the blood over the last two to three months.

A five-year study called the Diabetes Control and Complications Trial (DCCT) demonstrated that strict control of glucose levels through aggressive treatment and monitoring reduces the incidence of the damaging complications that can make diabetes such a debilitating disease.

The hemoglobin A1c test has long been an important part of diabetes management, but with the findings of the DCCT, the test’s ability to track long-term glucose control became even more significant. It is now a key component in managing the disease. This recognition led to guidelines on the frequency of testing and target levels that are reviewed regularly and occasionally updated, which is why target levels can change.

Laboratory tests such as cholesterol play a key role in medicine, but the information they provide is only one part of the clinical process that is designed to deliver improved outcomes. Cholesterol results are not considered alone, but in the context of your other risk factors.

Researchers are constantly looking for new and better tests, but often when a test is introduced, we lack a complete picture of its clinical context, and it can take time to know the correct way to apply the information it provides. This uncertainty can lead to problems when the media picks up on the latest great new test, and patients ask their physicians about it.

“There are...tests that have been really popular but we really don’t know where they fit,” said Robert Flaherty, a primary care physician who teaches about evidence-based medicine at Montana State University. “One is homocysteine. High levels of homocysteine are associated with increased risk of heart disease. But what we find is that if you decrease homocysteine levels, it does not seem to lower your risk.”

Flaherty draws a distinction between “treating a number,” such as a cholesterol level or a homocysteine level, and treating a patient. The ultimate reason for taking a cholesterol-lowering drug is to lower your risk of heart attack, and the clinical trials found the drugs were in fact lowering heart attack risk. But the context of the homocysteine test is still unclear.

“We have to realize what the lab test is telling us, and usually it is telling us of an association of a particular chemical and a disease,” said Flaherty. “So what we then need to do is to look to see whether treating that value and returning it to normal actually reduces the incidence of the disease.”