What Is Serum Cholesterol and Why Is It Important?

Cholesterol is often associated with heart disease. That’s because low-density lipoproteins (LDL) can build up in your arteries and restrict or block blood flow. Your body still needs a little cholesterol for healthy digestion and to make vitamin D and certain hormones.

Cholesterol is a type of fat. It’s also called a lipid. It travels through your bloodstream in tiny molecules wrapped inside proteins. These packages are called lipoproteins. LDL is one of the main types of lipoproteins in your blood. The other main type is high-density lipoproteins (HDL). A third type of lipid, called a triglyceride, also circulates in your blood.

Measuring your LDL (“bad” cholesterol), HDL (“good” cholesterol), and triglycerides will give you a number called your total blood cholesterol, or serum cholesterol. Your serum cholesterol levels can help your doctor figure out your risk for developing heart disease in the next 10 years.

Your serum cholesterol is measured with a simple blood test. A doctor draws blood from your arm — enough to fill one or more little vials. The blood samples are sent to a lab for analysis. Before your blood draw you’ll need to fast for at least eight hours.

A healthy adult should have a blood test that includes a serum cholesterol check every four to six years. As you get older, your doctor may advise you to have your cholesterol, and other markers of health like your blood pressure, checked every year. This is especially true if you have risk factors for cardiovascular disease. These factors include:

• obesity
• smoking
• family history of heart disease

If you start a new medication or change medications meant to manage your cholesterol, you’ll probably have more frequent cholesterol checks. Serum cholesterol tests can show whether the medication is working.

It usually takes several days or even a few weeks to get your blood test results back. Your lab report will show your serum cholesterol levels in milligrams per deciliter (mg/dL). Your serum cholesterol includes:

• LDL level
• HDL level
• 20 percent of your triglyceride level

The lower the LDL level and the higher the HDL level, the better. LDL is the type of cholesterol that forms waxy plaque on the inside wall of an artery. Too much plaque can limit blood flow through that artery.

Plaque can also rupture, spilling its contents of cholesterol, fats, and waste products into the blood vessel. As platelets rush to the injury, a blood clot can form. Platelets are a type of cell found in blood. If the clot is in an artery in the heart, called a coronary artery, a heart attack can occur. If the clot travels to the brain and blocks blood flow, the result is a stroke.

HDL cholesterol can help control your LDL cholesterol. HDL lipoproteins help move LDL particles out of the bloodstream. Higher levels of HDL are associated with better cardiovascular health. As for triglycerides, lower is better. When you eat, your body converts calories you don’t need for energy into triglycerides. Fat cells store the unused triglycerides. Consuming more calories than you burn will lead to weight gain and, often, higher triglyceride levels.

Calculating serum levels

Add your HDL and LDL cholesterol levels, plus 20 percent of your triglycerides, to calculate your serum cholesterol levels. If you have an LDL of 150 mg/dL, HDL of 35 mg/dL, and triglycerides of 180 mg/dL, your serum cholesterol would be 221 mg/dL. That’s considered a borderline high level. Your doctor would see that number as a warning sign and work with you on making changes that will bring your numbers down.

Here’s what you should look for in your results: