Date: October 1st, 2002
Cholesterol checks, mammograms, prostate exams-all these screenings have become routine as science discovers ways to detect disease at its earliest and most treatable stages. So what about new tests that have been gaining attention in news reports lately? Are they more hope, or just hype?
The truth is, some of both. There may be promising new blood tests on the horizon to help physicians determine which patients are at risk for developing heart disease. The increasingly widespread use of diagnostic imaging to screen for abnormalities, on the other hand, is being discouraged by public and private health agencies.
Here, we discuss a few of the tests doctors and patients are talking about. But first, a little background on how the medical community decides what screening procedures to recommend.
How do doctors decide what tests to administer?
Dr. Barbara Messinger-Rapport is a geriatrician at Cleveland Clinic Foundation and assistant professor of medicine at Case Western Reserve University. She says that the decision to use a particular procedure to screen for disease involves several criteria.
First, there should be a large enough incidence of the disease to merit spending the time and effort screening for it. Any recommended test also should be accurate and safe, Messinger-Rapport said, as well as well-tolerated and affordable to the patient. By the same token, it should have been proven effective in helping to fight a disease successfully. This last point is often the reason tests are not recommended for widespread use-yet.
High-sensitivity C-reactive protein blood test
C-reactive protein (CRP) is a substance the body produces in response to inflammation or infection. Scientists believe inflammation is directly related to arteriosclerosis, the accumulation of fatty build-up in the arteries.
Studies have found that a slightly elevated level of CRP in the blood may indicate a risk for this cardiovascular disease. The inflammation associated with arteriosclerosis produces very low levels of CRP. Normal CRP tests, which physicians may use to monitor other inflammatory diseases such as arthritis, do not measure levels of CRP this low. When screening patients for risk of heart disease, doctors will order a high-sensitivity CRP test.
The fact that inflammation is not unique to arteriosclerosis is one issue that threatens this test's usefulness in screening for heart disease.
"The C-reactive protein has long been associated with heart disease," Messinger-Rapport said. "However, it is also associated with hormone replacement, inflammatory arthritis, the common cold, and multiple other problems."
High-sensitivity CRP tests are not yet routinely used to measure cardiac risk, because the studies are preliminary and the exact role of CRP in relation to cardiovascular health has not yet been determined.
Homocysteine blood test
Homocysteine is an amino acid that the body produces when it breaks down proteins. Although a certain amount of homocysteine in the blood is normal, elevated levels of it have been associated with an increased risk of heart disease.
One exciting fact about homocysteine is what appears to be our ability to regulate it. The levels of this substance in the body are controlled by the B-complex vitamins, according to Dr. Jeffrey Blumberg, Professor of Nutrition at Tufts University.
By ensuring that our diets contain enough of these vitamins, we can regulate our levels of homocysteine. Studies are underway to determine whether using diet to lower levels of homocysteine will also lower the risk of heart disease.
Like CRP, there are no guidelines for screening for homocysteine because the studies are still in progress.
"They haven't yet done the study where you lower the level of homocysteine in people with elevated levels and show that they don't get heart disease," Blumberg said. "There are over a dozen clinical trials going on now. In five to fifteen years, the results of those studies will give you the definitive evidence."
Whole-body CT scans
Computerized tomography (CT) scanning, also known as CAT scanning, has been used for nearly 30 years as a diagnostic tool. It uses x-rays to generate images of cross-sections of the body.
Some medical imaging facilities are now promoting the use of CT scanning as a way to take a look inside the entire body and detect any abnormalities, such as tumors, at their earliest stages.
This may sound promising, but this use of CT scanning is not currently recommended by public or private health agencies. Several groups, including the U.S. Food and Drug Administration (FDA) and the American College of Radiology, have issued statements discouraging this use of CT scanning.
One reason is that the findings of the test may not be accurate. "Normal" findings, in which the scan detects no abnormalities, may be misleading and falsely reassure patients that nothing is wrong even if they begin to have symptoms, according to the FDA's statement.
On the other hand, CT scans sometimes pick up suspicious findings that then require further tests, many of which may be invasive, but turn out to be nothing but scar tissue or other benign abnormalities. This causes unnecessary anxiety, expense, and inconvenience to the patient.
CT scanning also subjects the patients to radiation exposure because of its use of x-rays. The benefits of using CT scans to diagnose a person with symptoms generally outweigh the risks; however, a person with no symptoms may simply be exposing themselves to radiation unnecessarily.
Finally, the FDA points out that no studies have proven that whole-body CT screening provides any certain benefit. Messinger-Rapport agrees with this assessment: "Whole body scans have not been demonstrated to reduce morbidity or mortality of any particular disease," she said.