Total Cholesterol: There’s a Cholesterol Formula for That

Your cholesterol level tells a lot about your risk for heart problems, but your total cholesterol depends on a formula involving different types of blood fats. And those individual numbers may be even more important.

According to the American Heart Association (AHA), the formula for calculating total cholesterol is simply adding up levels of HDL (high-density lipoprotein, the "good" cholesterol), LDL (low-density lipoprotein, the "bad" cholesterol) and 20 percent of your triglycerides. Triglycerides are a type of blood fat that contributes to the risk for cardiovascular disease, so a portion of this number is included in your total cholesterol.

Your total cholesterol number, however, is no longer useful by itself. "Total cholesterol is not as important as it used to be," says Luke Laffin, MD, a cardiologist in the preventive cardiology and rehabilitation section of the Cleveland Clinic's Heart and Vascular Institute. "It is no longer used in making a decision about your risk for heart attack or stroke, or used to make a decision about starting you on a cholesterol-lowering medication.

According to Johns Hopkins Medicine, cholesterol is a waxy substance that builds up inside your arteries, the blood vessels that carry blood away from your heart, creating growths called plaques. These plaques can narrow arteries and slow down or block blood flow. That, says the Centers for Disease Control and Prevention, is the main cause of cardiovascular disease that leads to a heart attack or stroke.

Cholesterol is not free-floating. It needs to be carried by proteins, and these proteins determine if cholesterol is good or bad, says Johns Hopkins. HDL proteins carry cholesterol away from your arteries, so HDL cholesterol is good and should be high. LDL proteins leave cholesterol in arteries, so this type of cholesterol is bad, Hopkins explains, and should be low.

Read more: What Is Cholesterol and Why Does Your Body Need It to Function Properly?

"Since new guidelines came out in 2013, we have moved away from using any single cholesterol number to make decisions about cardiovascular risk," Dr. Laffin says. "Numbers are now put into a 10-year risk calculator along with other risk factors like age, family history and high blood pressure."

The AHA says the best way to learn about your cardiovascular risk is to have a blood test every four to six years after age 20. If you have a history of cardiovascular disease or if you have risk factors, your doctor may want you to be tested more frequently. You should fast for nine to 12 hours before the test to get accurate results. To calculate your risk, the number from your test results will be plugged into a 10-year risk calculator.

The American College of Cardiology Risk Estimator Plus includes the following information:

• Age, sex and race.
• Blood pressure and if you take blood pressure medications.
• Total, HDL and LDL cholesterol numbers.
• History of diabetes.
• History of treatment with statin medications or low-dose aspirin.
  

The results of your risk evaluation will give you and your doctor a good idea of your chances of having a heart attack or stroke in the next 10 years and whether you need a treatment plan, according to Dr. Laffin.

Back when total cholesterol was thought to be an important number, home cholesterol kits were invented for people to check or calculate their total cholesterol at home.

"These home test kits are not needed because cholesterol numbers change slowly," says Dr. Laffin. "Cholesterol is not like blood sugar or blood pressure numbers that should be checked frequently. Even if you are on cholesterol medication, your cholesterol only needs to be checked once or twice a year. There is no need for frequent checks at home."

The AHA offers a cholesterol risk calculator you can use if you have your cholesterol numbers checked at a health fair or clinic. However, at-home calculations are not a substitute for a discussion with your doctor

Read more: The Truth About How Your Diet Affects Your Cholesterol