redOrbit Staff & Wire Reports – Your Universe Online
The formula currently used to calculate an individual´s “bad” cholesterol levels is often inaccurate, sometimes underestimating low-density lipoprotein (LDL) levels in those most at risk, researchers from the Johns Hopkins University School of Medicine have discovered.
Their study, published online in the Journal of the American College of Cardiology, explains that the Friedewald equation — which has been used to gauge a patient´s LDL levels since 1972 — is an estimate and not an exact measurement. It is currently used by doctors to assess a patient´s risk of having a heart attack due to the accumulation of plaque in arteries, but the new research calls its accuracy into question.
“In our study, we compared samples assessed using the Friedewald equation with a direct calculation of the LDL cholesterol. We found that in nearly one out of four samples in the ℠desirable´ range for people with a higher heart disease risk, the Friedewald equation had it wrong,” Seth Martin, lead author and clinical fellow at the hospital´s Ciccarone Center for the Prevention of Heart Disease, said in a statement. “As a result, many patients may think they achieved their LDL cholesterol target when, in fact, they may need more aggressive treatment to reduce their heart disease risk.”
“In patients with heart disease, we want to get their LDL level below 70 — that is the typical goal,” added Steven Jones, senior author and director of inpatient cardiology at The Johns Hopkins Hospital. Based on their findings, however, many people may falsely believe that their cholesterol targets have been met — especially those with high levels of triglycerides (a type of lipid or fat in the blood that can increase a person´s risk of cardiovascular disease).
Martin, Jones and their colleagues analyzed detailed lipid profiles for more than 1.3 million US adults dating from 2009 through 2011. The LDL cholesterol and blood lipid components in those samples had been measured using ultracentrifugation, a technique which uses a centrifuge to separate the particles so that they can be examined. They were then also evaluated using the Friedewald equation, and the results of each method were compared.
The Friedewald equation calculates LDL cholesterol using a specific formula — total cholesterol minus HDL cholesterol minus triglycerides divided by five, the researchers said. The result is then expressed in milligrams per deciliter. The Johns Hopkins team suggests an alternative method which they claim will be more accurate — the use of non-high-density lipoprotein (HDL) levels, in which the so-called “good” cholesterol is subtracted from total cholesterol.
The revised calculation would include not only LDL, but also very low density lipoprotein (VLDL) particles, which are also known to cause plaque in a person´s heart arteries. On average, the non-HDL reading would be approximately 30 points higher than LDL cholesterol readings calculated using the Friedewald method, the researcher said. That number could vary, though, and Martin believes it could provide a better measurement as to whether or not a patient needs to make specific lifestyle changes or alter his/her medications.
“Non-HDL cholesterol is a much better target for quantifying risk of plaques in coronary arteries,” Jones said. “Looking at non-HDL cholesterol would make it simpler and more consistent, and would enable us to provide our patients with a better assessment.”
In addition to Martin and Jones, authors of the study included Michael J. Blaha, Mohamed B. Elshazly, John W. McEvoy, Parag H. Joshi, Peter O. Kwiterovich, Andrew P. DeFilippis and Roger S. Blumenthal from Johns Hopkins; Eliot A. Brinton from the Utah Foundation for Biomedical Research and Utah Lipid Center; Peter P. Toth from the University of Illinois College of Medicine at Peoria; and Krishnaji R. Kulkarni and Patrick D. Mize from Atherotech Diagnostics Lab in Birmingham, Alabama.