What is cholesterol and why is it important?
Cholesterol is a molecule in the body that is required for multiple bodily functions. Cholesterol serves as a building block of cell membranes, is essential for normal brain development and function, and is needed for production of bile acids and hormones including cortisol, estrogen, testosterone, and vitamin D. Because cholesterol is hydrophobic (i.e., insoluble in water), it cannot be transported on its own in water or blood. It instead needs to travel in a hydrophilic particle (one that is soluble in water), a lipoprotein. Lipoproteins are particles made up of protein and fat (lipids) and they enable absorption and transport of lipids by the small intestine, transport of lipids between the liver and peripheral tissues, and peripheral tissues and the intestine. Cholesterol and triglycerides are both lipids that are transported by lipoproteins.
Do we make our own cholesterol?
Approximately 25% of the cholesterol in the body comes from the food we eat, and approximately 75% comes from the cholesterol produced in the body.
How can I interpret the lipid panel labs that my doctor orders?
Total cholesterol measures the total cholesterol in the blood that includes HDL cholesterol, LDL cholesterol, and VLDL cholesterol (very low-density cholesterol).
Low density lipoprotein (LDL) carries 60-70% of the circulating cholesterol. LDL-C measures the amount of cholesterol estimated to be associated with LDL particles. LDL particles vary in size and density. The small, dense ones are associated with metabolic syndrome and are more atherogenic (i.e., more likely to lead to plaque formation in the arteries) than large LDL particles. While it is not a part of the basic lipid panel ordered, a panel may be ordered that assesses LDL particle size and number.
Very low-density lipoprotein (VLDL) is also associated with atherosclerosis.
Triglycerides are a type of lipid also carried in lipoproteins that are associated with atherosclerosis.
Apolipoprotein B 100 (ApoB) is synthesized in the liver and carries lipids including low-density lipoprotein (LDL), very low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), and lipoprotein (a). Each LDL particle contains one ApoB-100 molecule. High level of ApoB-100 is associated with atherosclerosis (plaque buildup in the artery walls).
Lipoprotein (a) – Lp(a) is a lipoprotein made by the liver. It is made up of ApoB100 and apolipoprotein(a). Lp(a) is thought to be atherogenic and thrombogenic (increases the risk of blood clots). High levels increase the risk of heart attack or stroke, blood clotting, or stiffening of the aortic valve in the heart. For more on Lp(a), you may read this article.
High density lipoprotein HDL-C measures the cholesterol associated with HDL particles that help to remove cholesterol from artery walls. Having a normal amount of HDL-C is favorable, while having low levels increases cardiovascular risk. Interestingly, extremely high levels of HDL-C have been associated with cardiovascular disease risk and increased mortality.
Hs-CRP stands for high sensitivity C-reactive protein, which is a measurement of inflammation in the body. While this is not a measure of cholesterol, it is an important cardiovascular risk factor, that should be ordered with a lipid panel in the context of assessing cardiovascular risk. Of note, CRP can also be elevated due to an infection, inflammation from an autoimmune condition, intestinal hyperpermeability (leaky gut), metabolic syndrome, or a dental condition such as gingivitis or periodontitis, so it is important to note that other conditions can be confounding factors to the measurement.
Lipoprotein-associated phospholipase A1 (Lp-PLA2) is an inflammatory enzyme that circulates bound to low density lipoproteins. It is located in atherosclerotic plaques. In clinical trials, it has been shown to be an independent predictor of coronary artery disease and stroke.
TMAO (trimethylamine N-oxide) is a metabolite resulting from consumption of foods such as red meat, certain types of seafood, egg yolk or full fat dairy. They contain nutrients including lecithin, choline and L-carnitine, which the gut bacteria metabolize to TMA. TMA is the transported to the liver and converted to TMAO. TMAO has been found to promote atherosclerosis. Mediterranean diet has been shown to inhibit TMAO production.
For a more detailed reference on lipids and lipoproteins, you may refer to this article.
When you have your blood work done, the lab will provide a reference range for components that are part of your lipid panel. While the reference ranges may be a helpful guide, it is important to interpret your values with your physician, in the context of your health, risk factors and goals. One of the important risk factors is family history. If you know your family history of cardiovascular disease (e.g., heart attack or stroke and the age of each relative when they had such events), it is important to share this information with your doctor, as this information may affect their recommendations.
Typical reference ranges:
Total cholesterol below 200mg/dL.
LDL cholesterol below 100mg/dL – or < 70mg/dL for individuals at high risk of heart attack or stroke, presence of cardiovascular disease or prior history of heart attack or stroke.
HDL cholesterol equal to or greater than 60mg/dL (if you have CardioIQ panel, you will see that according to their ranges, greater than 50mg/dL is optimal)
Non-HDL cholesterol below 130mg/dL or less than 100mg/dL for individuals at risk of heart attack or stroke.
Triglycerides below 100mg/dL (some labs note that below 150 is an acceptable range).
Apolipoprotein B below 80mg/dL (20th percentile) or less than 90mg/dL (CardioIQ); some reference ranges cite below 130mg/dL or 100mg/dL; note that some physicians advocate for much more aggressive control of <60mg/dL (5th percentile), depending on one’s age and risk factors.
Lipoprotein (a) – Lp(a) – optimal level is < 75nmol/L; this is highly genetically determined
Hs-CRP optimal value is < 1. Elevated CRP should be discussed and worked up with your physician.
Lp-PLA2 Activity < 123 nmol/min/mL is considered optimal.
TMAO < 6.2 microM is considered optimal.
Genetic make-up, nutrition, and lifestyle can contribute to high cholesterol. Common lifestyle factors that contribute to unfavorable lipid profile include include sedentary lifestyle, diet (high saturated fats and trans fats intake; for e.g., animal products including red meat, as well as commercially baked goods, fried foods, and processed food), alcohol consumption, smoking and stress.
What do I need to know before getting a lipid panel?
Discuss the above markers with your physician and whether it may be appropriate to order them. Additionally, in our practice, we typically recommend that a patient fasts before the lipid panel as triglyceride levels can significantly go up after a meal. A 9 hour fast will typically suffice. Alcohol consumption can also increase triglycerides, and it is generally not recommended to drink alcohol 24 hours before a fasting cholesterol.