You try to be a good patient. You schedule your general physical with your primary doctor every year. Your doctor sends you for blood work, which you have done. Once the results are available, you log into your patient portal. There they are, your lab results. However, you are confused. What do all those initials mean? What do the numbers mean? Which ones are relevant? Which ones should you ignore? Here is a general primer on how to read your lipid panel blood test.
Before we look at some test results, we need some definitions. Lipids are a broad group of molecules that include cholesterol, triglycerides, fatty acids and others. Lipids are involved in many biologic functions. Lipids don’t dissolve in the blood and have to be transported from where they enter the body (or are stored) to the site where needed. Apolipoproteins carry out the transportation of lipids.
Now, let’s walk through some typical lipid panel results. We’ll start with the panel pictured above. The first line is Total Cholesterol, which in this case is 121 mg/dl. In general, cholesterol levels should be below 200 mg/dl. Total cholesterol is a marginally useful number. The next line shows the triglycerides, which are 46 mg/dl. Triglycerides are the fat in the blood. When we eat food, any excess calories are turned into triglycerides and stored in fat cells. When extra energy is required by the body, the triglycerides are released and used. Triglycerides and cholesterol are different types of lipids. Triglycerides are used for energy while cholesterol is used to build cells and proteins. A normal triglyceride level is less than 150 mg/dl. An elevated triglyceride level (over 150 mg/dl) is associated with excess risk for heart artery disease, heart attack and cardiac death. The next line is HDL Cholesterol at 67 mg/dl. HDL stands for High Density Lipoprotein. It is the “good” cholesterol. HDL transports excess cholesterol in the body back to the liver where it is metabolized and excreted. HDL is important. Low levels of HDL have consistently been associated with heart artery disease. However, the converse is not true; high levels of HDL do not protect against heart artery blockage, contrary to the urban myth that it does. Many patients when asked why they are not on medication for their high cholesterol state that it is because they have a high HDL. HDL levels above 39 mg/dl are ideal. Many studies involving many different medications have been tried to raise HDL. Unfortunately, no pharmacologic therapy has been proven to raise HDL and reduce cardiac outcomes. The next line is VLDL Cholesterol Cal at 11 mg/dl. VLDL stands for Very Low Density Lipoprotein and these particles travel with triglycerides. The VLDL value is not measured but calculated (thus the ”Cal”) as trigylcerides divided by 5. It is not a clinically useful value and can be ignored.
The next line is the most important, LDL Chol Calc (NIH) at 43 mg/dl. LDL is Low Density Lipoprotein and this can be reported in two different ways. It can be measured directly, which not the usual case as it is difficult. Most of the time, it is a calculated value. There are at least three different formulas for calculating LDL. The simplest is the Friedewald equation where LDL= total cholesterol- (HDL+triglycerides/5). Other equations are the NIH (which is the one used in the example) and Martin-Hopkins formula. There are differences in the equations, but a recent study found that the differences are small and not clinically significant. Excess LDL builds up in the artery wall, forming plaque and leading to blockage which results in a heart attack or stroke. As the average LDL level rises, the chance of atherosclerosis/plaque goes up and the number of sites affected goes up as well. In general, the LDL should be less than 100 mg/dl. In patients who have had a heart attack or stroke or had a stent or heart bypass, the LDL goal is less than 70 mg/dl or even lower. The last line is the LDL/HDL ratio. This number is irrelevant and can be ignored; just concentrate on the actual numbers, especially LDL, HDL and triglycerides.
So, this is how to interpret the basic lipid panel. What about advanced tests? What is available? What is useful? There is a test called the NMR Lipoprofile. It reports more in-depth parameters such as particle size and density. While there is some slight incremental value in these numbers in terms of cardiac risk evaluation, no cardiac society recommends it. The consensus is that the standard lipid panel is good enough to estimate and follow risk. One test that may be beneficial is Apo B. Remember that apolipoproteins transport cholesterol in the blood. Apo B is one of those transport proteins and it carries all of the atherogenic lipids: LDL, VLDL and Lipoprotein a (more about this in a bit). So, measuring Apo B gives a very good sense of how much risk of atherosclerosis is present. Apo B is a more accurate marker of cardiac risk than LDL or non HDL cholesterol. The difference may or may not be clinically relevant. Currently, Apo B is not routinely checked but that may change in the future. Lipoprotein a is a lipid particle that is 5 times more atherogenic than LDL. It runs in families and it is estimated that one in five people have an elevated lipoprotein a level. A lipoprotein a level should be checked if there is a strong family history for premature heart artery disease or if a patient has recurrent heart attacks despite low levels of LDL. Lipoprotein a levels less than 75 mg/dl are considered normal.
In summary, the basic lipid panel provides enough information for risk assessment and for following progress in the prevention of coronary artery disease. The important numbers to pay attention to, in order, are: LDL, HDL, Triglycerides, non HDL cholesterol and finally total cholesterol.
Additional resources:
LDL:
http://sportscardiology.blogspot.com/2022/03/cholesterol-years.html
HDL:
http://sportscardiology.blogspot.com/2022/10/how-high-is-too-high.html
Triglycerides:
http://sportscardiology.blogspot.com/2023/11/the-trouble-with-triglycerides.html
Lipoprotein a:
http://sportscardiology.blogspot.com/2021/04/
