At a glance
Also known as
LDL Subclasses; LDL Subfractions; HDL Subclasses; HDL Subfractions
Why get tested?
To help evaluate your risk of developing coronary artery disease (CAD)
When to get tested?
This type of testing is only available through research or other specialised laboratories in Australia and is rarely used at present
A blood sample drawn from a vein in your arm
Test preparation needed?
You may need to fast for 9-12 hours before this test
What is being tested?
Lipoprotein subfraction tests separate the commonly measured lipoprotein fractions LDL (Low Density Lipoprotein, often called the bad cholesterol) – into subfractions based on the size, density, and/or electrical charge. Rarely testing may also identify subfractions of VLDL (Very Low Density Lipoprotein, also considered to be a bad cholesterol) or HDL (High Density Lipoprotein, often called good cholesterol).
Lipoproteins are a group of particles that are responsible for transporting lipids throughout the body. Each particle contains a combination of , cholesterol, triglyceride, and molecules. The composition of the particles change as they circulate in the blood; some molecules are removed and others are added. The result of this dynamic process is a spectrum of LDL, HDL, and VLDL lipoprotein particles that vary from large and fluffy (those with a high proportion of triglycerides) to small and dense (those with a high proportion of cholesterol).
Some studies have shown that small dense LDL particles are more likely to cause than light fluffy LDL particles. Researchers think that the presence of small dense LDL could be one of the reasons that some people have heart attacks. This may be the main reason is why LDL is referred to as the bad cholesterol. Small dense VLDL particles (known as remnants) are also thought to increase risk of atherosclerosis. However, the data are not clear on whether testing for subfractions provides additional information compared to an ordinary lipid profile about a person’s cardiac risk or whether results from such testing should affect decisions about treatment.
The number of small dense LDL, VLDL, and HDL particles a person has is partially genetically determined, partially due to gender (males tend to have more small LDL and HDL than females), and partially due to lifestyle and a person’s general state of health. Certain diseases and conditions, such as diabetes and hypertension, are associated with increased levels of small dense LDL.
Patient who have diabetes or obesity often have elevated triglycerides and low HDL and these findings are predictive of small dense LDL.
A variety of methods are used to determine lipoprotein subfractions in research laboratories. These include ultracentrifugation (separation by density), electrophoresis (separation by charge and size), and NMR (nuclear magnetic resonance) spectroscopy (which counts the number of particles in each subfraction). Until recently, these methods were too expensive and technically demanding to be used on a commercial basis and in Australia, LDL subfraction testing is not covered by Medicare.
A summary of draft guidelines on Emerging Biomarkers of Cardiovascular Disease and Stroke from The National Academy of Clinical Biochemistry states “Lipid subclasses, especially the number or concentration of small dense LDL particles, have been shown to be related to the development of initial coronary heart disease events, but the data analyses of existing studies are generally not adequate to show added benefit over standard risk assessment. There is insufficient data that measurement of lipid subclasses over time is useful to evaluate the effects of treatments.”
Although less is known about HDL subclasses, some initial studies have shown that large fluffy HDL particles may provide more protection against atherosclerosis than small dense HDL particles.
More clinical research is needed to determine whether there is value in testing for lipoprotein subfractions and how the results may be used.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
Is any test preparation needed to ensure the quality of the sample?
Fast for 9-12 hours prior to the test or as requested by your doctor.