LDL Particle Testing (LDL-P)
When you have a personal and/or family history of CVD at an early age; when the result of your low-density lipoprotein (LDL) cholesterol test is within a healthy range, but your healthcare provider thinks that you may have an increased risk of developing heart disease; sometimes to help monitor the effectiveness of lipid-lowering treatment and/or lifestyle changes
A blood sample drawn from a vein in your arm
You may need to fast for 9-12 hours before this test; only water is permitted. Follow any instructions you are given.
Lipoproteins are particles that transport fats throughout the body. These particles are essential and carry a combination of proteins, vitamins, cholesterol, triglyceride, and phospholipid molecules. The composition of a lipoprotein particle changes as it circulates in the blood. Some molecules are removed and others are added, resulting in lipoprotein particles with variable amounts of cholesterol.
Low-density lipoprotein particles (LDL-P) are bi-products of fat transport that remain in circulation for an extended time. While in circulation, LDL-P can penetrate the artery wall and get stuck, forming a fatty plaque. These plaques can build over time and lead to blockages, resulting in heart attacks and strokes. The likelihood of an LDL-P getting trapped in the artery wall increases when more LDL-P are in the blood.
Traditional lipid testing measures the amount of LDL cholesterol (LDL-C) present in the blood, but it does not evaluate the number of LDL particles (LDL-P). LDL-P is often used to get a more accurate measure of LDL due to the variability of cholesterol content within a given LDL. Studies have shown that LDL-P more accurately predicts risk of cardiovascular disease than LDL-C. Researchers think that increased LDL-P could be one of the reasons that some people have heart attacks even though their total cholesterol and LDL cholesterol levels are not particularly high.
How is the test used?
Low-density lipoprotein particle (LDL particle or LDL-P) testing evaluates LDL particles according to their concentration in the blood. It may provide useful information for assessing your cardiac risk if you have a personal or family history of heart disease at a young age, especially if your total cholesterol and LDL cholesterol (LDL-C) values are not significantly elevated.
While for many people, the standard LDL-C test is a good indicator of risk of cardiovascular disease (CVD), research has found that some people with healthy levels of LDL-C still have increased risk of CVD. Similarly, individuals with some chronic conditions such as diabetes may have increased risk even though their LDL-C is at a healthy level. For these populations, it has been suggested that the number of LDL particles might be an additional factor to consider when determining their CVD risk. In these cases, LDL-P testing may be used to further evaluate an individual's CVD risk.
LDL-P may also be occasionally ordered to monitor the effectiveness of treatment.
LDL subfraction testing is typically done along with LDL-P, however, subfraction information should not guide decision-making. Laboratories use a variety of methods to determine lipoprotein subfractions, including ultracentrifugation, polyacrylamide gradient gel electrophoresis, and NMR spectroscopy. None of these methods are harmonized, nor do they agree on the definitions of large versus small subfractions. None of the LDL subfraction methods in clinical use have sought Food and Drug Administration (FDA) clearance for subfractionation of LDL.
The National Lipid Association (NLA) has specifically called out the terms "large and fluffy LDL" as potentially misleading as it should be emphasized that all LDL is able to form arterial plaques. Importantly, patients with Familial Hypercholesterolemia, who develop heart attacks at an extremely young age, have "large and fluffy" LDL.
Data do not support routine testing for lipoprotein subfractions. Nevertheless, LDL subfraction testing has been used in clinical settings. No medical society has endorsed the use of lipoprotein subfractions. The National Lipid Association, the National Academic of Clinical Biochemistry, the American College of Cardiology, and the American Heart Association have all published guidelines specifically recommending against the use of LDL subfractions. The guidelines cite a lack of sufficient evidence to support LDL subfraction measurement for initial clinical assessment or on-treatment management decisions.
When is it ordered?
This testing may be ordered as part of an overall evaluation of cardiac risk when you have a personal or family history of early cardiovascular disease (CVD), especially when you don't have typical cardiac risk factors, such as high cholesterol, high LDL cholesterol, high triglyceride, low HDL cholesterol, smoking, obesity, inactivity, diabetes, and/or hypertension.
Your healthcare practitioner may order LDL-P testing, along with other lipid tests, after you have made lifestyle changes and/or been treated with lipid-lowering medications to determine whether treatment is working.
Although it is not generally recommended as a screening test, a few healthcare providers are ordering LDL-P along with a battery of other cardiac risk tests when they are attempting to determine someone's overall risk of developing CVD.
What does the test result mean?
LDL-P test results are typically reported according to the testing method the laboratory uses. The report will usually include results for your total cholesterol, LDL-C and LDL-P. Additional values might include very low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), LDL-C and/or HDL cholesterol, particle and size. Since different lab methods separate the subclasses based on different physical properties (particle number, size, density, and/or electrical charge), results cannot be directly compared between methods or laboratories.
In general, the result is interpreted within the framework of a lipid profile and its associated risk. If you have an increased LDL-P, this finding will add to your risk of developing cardiovascular disease above and beyond the risk associated with LDL cholesterol.
Is there anything else I should know?
It is important to remember that LDL subfraction testing is not diagnostic, not endorsed by any medical societies, and not approved by the FDA. It attempts to evaluate your risk of developing CVD, but it cannot predict the development or severity of disease in a particular person. For this reason, LDL subfraction results should not be considered when making decisions about treatment or lifestyle changes.
How can I decrease my LDL-P?
LDL-P can be altered by adopting a reduced-calorie diet, losing excess weight, and exercising regularly. The use of lipid-lowering drugs such as statins and PCSK9-inhibitors will significantly reduce LDL-P.
How long will it take for my results?
It depends on the laboratory performing the test. Not every lab performs LDL-P testing as it requires specialized instruments. Your sample may be sent to a reference laboratory for testing, so it may take several days before results are available.