Lipoprotein Subfraction Testing

Lipoprotein subfraction testing is not routinely ordered, but its use is growing. It may offer useful information in assessing risk in patients who have a personal or family history of early heart disease, especially if their total and LDL cholesterol values are not significantly elevated. LDL subfraction testing is more common than VLDL or HDL subfraction testing since LDL has been identified as the primary risk factor for heart disease and more research and development has focused on LDL measurement.

Subfraction testing is typically done along with a lipid profile. The subfractions are usually expressed as relative proportions or percents of the LDL, VLDL, and/or HDL.

Since subfractions may be affected by lipid treatment and/or lifestyle changes, LDL subfraction testing may also be occasionally ordered to monitor the effectiveness of treatment in decreasing the number of small dense LDL particles.

Lipoprotein subfraction testing may be ordered as part of an overall evaluation of cardiac risk when someone has a personal or family history of early CAD, especially when they don’t have typical cardiac risk factors, such as high cholesterol, high LDL, high triglyceride, low HDL, smoking, obesity, inactivity, diabetes, and/or hypertension.

When a patient with a large proportion of small dense LDL particles has undergone lipid lowering treatment or lifestyle changes, his doctor may order LDL lipoprotein subfraction testing, along with other lipid tests, to monitor the effectiveness of treatment.

Although it is not generally recommended as a screening test, a few doctors are ordering lipoproteins subfraction testing along with a battery of other cardiac risk tests when they are attempting to determine a patient’s overall risk of developing CAD.

In general, the result is interpreted within the framework of a lipid profile and its associated risk. If the patient has primarily small dense LDL, this finding will add to the risk of developing CAD above and beyond the risk associated with the total LDL. On the other hand, the presence of exclusively large fluffy LDL will add no additional risk. The interpretation of the VLDL subfraction is similar. The picture is more complex with HDL subfractions, however, and there is no consensus on how to include the findings in risk assessment, but in general the presence of large fluffy HDL is thought to offer more protection than small dense HDL.

It is important to remember that lipoprotein subfraction testing (and other lipid and cardiac risk factor testing) is not diagnostic. It attempts to evaluate a patient’s statistical risk of developing CAD, but it cannot predict the development or severity of CAD in a particular patient.

Results of lipoprotein subfraction testing reflect the method and reporting format used as well as the patient’s total LDL-cholesterol, VLDL, and/or HDL-cholesterol. Since different methods separate the subclasses based on different physical properties (size, density, and/or electrical charge), results may not be directly comparable method to method or laboratory to laboratory.