Cholesterol, which your body needs to function normally, is found throughout your body in many different tissues. However, too much cholesterol in the body leads to a buildup of a wax-like substance in blood vessels. Cholesterol buildup can block the flow of blood through the arteries and may lead to heart disease. Cholesterol tests will tell you if your cholesterol levels are in the normal healthy range or unhealthy ranges, which may require treatment.
Types of Cholesterol
Cholesterol tests differ based on the type of cholesterol being tested. Commonly tested cholesterol types include total cholesterol; high-density lipoprotein, or HDL; and low-density lipoprotein, or LDL. HDL and LDL are the two types of cholesterol that transport fat through the bloodstream and together they make up total cholesterol. HDL is composed of fat, a large amount of protein and a small amount of cholesterol. LDL is made of fat, a large amount of cholesterol and a small amount of protein. HDL is considered "good" cholesterol because it is removed from the body by the liver. In contrast, LDL is considered "bad" cholesterol because it is gets deposited in blood vessel walls.
Types of Cholesterol Tests
The most common types of cholesterol tests are the non-fasting tests to measure total cholesterol and HDL cholesterol levels. This test is accurately able to measure these types of cholesterol because these values do not change very much when you eat. Another type of cholesterol test is the indirect fasting LDL cholesterol test. This test has to be conducted after you have fasted for nine to 12 hours because LDL cholesterol levels change after eating. In this test, LDL cholesterol is measured indirectly by subtracting HDL and 0.2 x triglycerides from total cholesterol. More recently, a direct LDL test has been developed that measures LDL cholesterol, and these tests do not require fasting. However, the direct LDL cholesterol test is much more expensive then indirect fasting tests.
Getting the Test
Cholesterol is tested from blood sampled from a vein, often the vein located inside the elbow. The nurse first increases the volume of blood in the vein by tying an elastic band around the upper arm, and then disinfects the skin with an antiseptic swab. The nurse takes the blood sample by inserting a needle-tipped syringe into the vein, and the blood is collected into a sterile tube. The blood sample is then sent to the lab and tested according to the type of cholesterol test ordered.
Interpreting the Results
Depending on whether total, HDL or LDL cholesterol is being tested, different results are desirable. It is healthiest for total cholesterol to be below 200 mg/dL and LDL cholesterol to be below 100 mg/dL. In contrast, a desirable HDL cholesterol level is above 40 mg/dL.
