Evidence
has been building for several years that painless inflammation can cause heart
trouble and may even be more dangerous than high cholesterol. But until now,
doctors have had no formal guidelines to tell them how or when to look for
inflammation, which can be measured with a simple blood test
A
panel of experts convened by the American Heart Association and the Centers
for Disease Control and Prevention is recommending limited use of a new blood
test that has been widely promoted for assessing heart disease risk.
That recommendation and others regarding the role of the blood test are
published in last week’s Circulation: Journal of the American Heart
Association.
How
does inflammation relate to heart disease and stroke risk?
"Inflammation"
is the process by which the body responds to injury. Laboratory evidence and
findings from autopsy studies suggest that the inflammatory process plays an
important part in atherosclerosis (ath"er-o-skleh-RO'sis). That's the
process in which fatty deposits build up in the lining of arteries.
C-reactive
protein (CRP) is a protein in the body whose level increases when there's
inflammation of blood vessels. It's been suggested that CRP may provide a new
way to assess cardiovascular disease risk.
Researchers
have found that blood levels of CRP are elevated many years before a first
heart attack or stroke. One important study was published in the April 3,
1997, New England Journal of Medicine.
Using
a test called high-sensitivity testing for CRP, the researchers measured
baseline levels of CRP among 1,086 apparently healthy men participating in the
Physicians' Health Study. These men were then followed over an eight-year
period for future development of their first heart attack, stroke or venous
thrombosis (blood clot in a vein).
What
is the CRP test?
The
test is the highly sensitive C-reactive protein (hs-CRP) test. CRP is an
inflammatory marker found in the blood. Several studies have
demonstrated that increased concentrations of CRP appear to be associated with
increased risk for coronary heart disease, sudden death and peripheral
arterial disease.
Thomas
A. Pearson, M.D., Ph.D., co-chair of the AHA/CDC writing group, says there is
“no need for hs-CRP screening of the entire adult population as a
public-health measure.”
George
A. Mensah, M.D., co-chair of the writing group and chief of the cardiovascular
health program at the CDC, explains: “For clinicians and public health
practitioners, it is important to emphasize that although abnormal CRP values
identify high risk persons, we have no evidence that treatment strategies
based on CRP levels improve survival or reduce cardiovascular complications.
“Although
our statement identifies a subgroup of patients who may benefit from hs-CRP
testing, for most patients the emphasis must remain on detection, treatment,
and control of the major risk factors, such as high blood pressure, high blood
cholesterol, cigarette smoking and diabetes,” adds Mensah.
Pearson
says the test might be useful when a physician is undecided about a course of
treatment for a patient who is considered intermediate risk.
For
example, a person at intermediate risk may be someone considered to have a 10
percent to 20 percent risk for heart attack in the next 10 years based on his
or her current health status and history. “In those cases, an CRP test
might tip the scale to help a physician decide on moderate or more intensive
treatment,” he says.
CRP,
a chemical necessary for fighting injury and infection, is made in the liver
in response to inflammation somewhere in the body. While high cholesterol
causes fatty buildups in the blood vessels, heart attacks are triggered when
inflammation causes the deposits to break off and clog an artery.
The
AHA/CDC group reports that the results of CRP tests should be expressed as
milligrams per Liter (mg/L) with concentrations of less than 1.0 mg/L defined
as low risk, 1.0-3.0 mg/L as average risk and concentrations higher than 3.0
mg/L defined as high risk. People in the high-risk group have about a
two-fold increase in relative risk for cardiovascular disease compared to
those in the low-risk group.
CRP
can be lowered by the same strategies that decrease cholesterol -- exercising,
weight loss, stopping smoking and statin drugs. The first new blood test
accepted for assessing heart disease risk since cholesterol screening became
common 30 years ago, it costs a few dollars to perform, and labs and hospitals
charge $10 to $120.
The
guidelines recommend against testing people at very low risk, since they
likely wouldn't be put on heart treatment even if inflammation were found, and
those already diagnosed with heart disease, since they should already be
getting all standard treatments.
The
Recommendations
Pearson
says the new recommendations set down these evidence-based parameters for
using CRP:
No
need for CRP screening of the entire adult population as a public health
measure.
CRP
can, however, be an independent marker of risk and may be useful as a
discretionary tool for evaluating people with moderate risk.
There
is not enough evidence to suggest using CRP to track the efficacy of
treatment.
The
average CRP reading in this country is 1.5. The risk is dramatically higher
when the levels hit 3, studies show.
Another
study in last week’s Circulation suggests CRP levels may also help predict
heart attack risk in women with metabolic syndrome, a condition linked to
obesity, impaired metabolism of blood sugar, high blood pressure and high
levels of blood fats.
Women
with the syndrome and CRP levels 3 or higher are twice as likely to have a
cardiovascular event than those with CRP levels of 1, the study showed.
Both
Pearson and Mensah emphasize that the new recommendations are based on current
evidence, and may need to be changed as new clinical trial results become
available.
