Interpreting Your Test
Part 1- The different types of cholesterol tests, and what they tell you
Most people have heard of cholesterol, and many of us have had our cholesterol measured before in one way or another. There are, however, many different ways to measure cholesterol and interpreting the results can be confusing. Here we will take a look at several different types of cholesterol testing and what information can be gleaned from each.
Before we do that though, lets take a brief detour to discuss why we even care about our blood levels of cholesterol in the first place. In other posts we discussed what cholesterol is and the ways cholesterol can harm our body. To review briefly, lipid
filled particles, also called lipoproteins, ferry cholesterol and triglycerides around in your bloodstream. Over time these particles can get stuck in the walls of your arteries, ultimately causing blockages (also known as atherosclerosis like what is shown in the drawing above), and eventually leading to heart attacks or strokes. These lipoprotein particles are named according to their density; in other words...how they float in water. The main particles that are at risk for getting stuck in the artery walls and leading to atherosclerosis are unimaginatively named: Low Density Lipoprotein (LDL), and Very Low Density Lipoprotein (VLDL), with the LDL particles being far more numerous. High Density Lipoprotein (HDL) particles do not get trapped in the artery wall and therefore do not contribute to overall risk. LDL particles have generally received the most attention, but studies have demonstrated without a doubt that VLDL particles are dangerous as well. And research has also clearly told us that the more particles (both LDL and VLDL) there are floating around the higher the risk of things like heart disease. This is ultimately why we measure cholesterol- to estimate risk of complications such as heart attack and stroke, and to help guide treatment decisions.
Broadly speaking, there are 2 pieces of information given by the various lipid tests: 1) How much cholesterol is contained in the particles, and 2) How many particles there are. To help visualize the difference, take a look at the cartoon of the different balloons shown here. If I were to describe the balloons only by telling you how much air is contained within them, you would be confused. You'd
have no idea if I was talking about the single ballon on the left which is filled with lots of air, or the couple balloons in the middle each of which have a moderate amount of air, or the numerous balloons on the right that each contain only a small amount of air. At the end of the day, each set contains the same total amount of air. The same concept applies to lipoprotein particles (balloons) and the cholesterol (air) contained within them. As it turns out, if your cholesterol particles look like the balloons on the right you are at far higher risk of heart attacks and strokes than a person represented by the balloon on the left. To get an accurate picture, sometimes more than one piece of information is needed... but you have to be willing to look a little deeper!
Your standard lipid profile contains the following information: Total cholesterol, HDL cholesterol, LDL cholesterol and Triglycerides. Let's take a look at what each of these means.
-Total Cholesterol: This is the amount of cholesterol that is held within all of the lipoprotein particles in a given amount of blood (typically 1/10th of a liter).
-Triglycerides: Just like the total cholesterol above, this is the amount of triglycerides that are held within all of the lipoprotein particles (mostly VLDL) in that same amount of blood.
-HDL Cholesterol: This is the amount of cholesterol that is held within just your HDL particles in a given amount of blood.
-LDL Cholesterol: This is the amount of cholesterol in just your LDL particles. Typically this is where most of your blood cholesterol resides. It is important to realize that this number is generally calculated rather than directly measured. While most of the time estimation works ok, there are many factors that can influence this calculation and make the results less reliable.
Many times the lipid profile will also include a VLDL cholesterol, which you may have guessed is the cholesterol contained within your VLDL particles. Like the LDL cholesterol, this value is calculated based on your triglyceride level.
Here we took a look at the reasons why it is good to know your cholesterol levels, as well as what is measured in a standard lipid profile. In part 2 we will examine in more depth how to interpret these numbers, their limitations, as well as some other tests which can sometimes give us additional information.