A new formula to calculate "bad" cholesterol or low-density lipoprotein (LDL) cholesterol - which can increase the risk of heart attack and stroke - has been developed.
If confirmed and adopted by medical laboratories that routinely calculate blood cholesterol for patients, the researchers say their formula would give patients and their doctors a much more accurate assessment of LDL cholesterol.
"The standard formula that has been used for decades to calculate LDL cholesterol often underestimates LDL where accuracy matters most - in the range considered desirable for patients at high risk for heart attack and stroke," said Seth S Martin, a cardiology fellow at the Johns Hopkins Ciccarone Center for the Prevention of Heart Disease.
Many studies have shown that higher levels of LDL cholesterol signal greater risk of plaque accumulating in heart arteries.
Since 1972, a formula called the Friedewald equation has been used to gauge LDL cholesterol. It is an estimate rather than a direct measurement.
However, physicians use the number to assess their patients' risk and determine the best course of treatment.
That equation, the researchers say, applies a one-size-fits-all factor of five to everyone; a more accurate formula would take specific details about a person's cholesterol and triglyceride levels into account.
Using a database of blood lipid samples from more than 1.3 million Americans that were directly measured with a traditional and widely accepted technique known as ultracentrifugation, the researchers developed an entirely different system and created a chart that uses 180 different factors to more accurately calculate LDL cholesterol and individualise the assessment for patients.
"We believe that this new system would provide a more accurate basis for decisions about treatment to prevent heart attack and stroke," said Martin.
The researchers compared samples assessed using the Friedewald equation with a direct calculation of the LDL cholesterol.
The lipid profiles used for the study were from a laboratory in Birmingham, which provides a detailed analysis of samples sent in by doctors across the country.
That database was almost 3,000 times larger than the sample used to devise the Friedewald equation 43 years ago.
The study was published in the Journal of the American Medical Association.
