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The page below is a sample from the LabCE course Emerging Cardiovascular Risk Markers. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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ApoB/ApoA1: The Test

Measuring ApoB to quantitiate LDL particles and using ApoA1 to quantitate HDL particles is newer way to try and assess cardiovascular risk. ApoB and ApoA1 can be performed using standard immunoassay techniques. Nephelometry assays for these proteins are popular as are ELISA-based methods that are performed on automated chemistry analyzer platforms.

The power of the ApoB/ApoA1 ratio as a cardiovascular risk marker has been slowly getting more attention. An individual with seemingly normal LDL-C may in fact have high ApoB concentrations. When this individual has his or her ApoB/ApoA1 ratio calculated, this risk is unmasked. Studies have also shown that patients with metabolic syndrome and type-2 diabetes can also easily be identified with the ApoB/ApoA1 ratio, whereas these patients cannot always be identified by measuring LDL-C and HDL-C.

In 2004, the global INTERHEART study of risk factors for acute myocardial infarction concluded that the ApoB/ApoA1 ratio was the most important risk factor in all geographic regions. The ApoB/ApoA1 ratio is easy to use because the risk is integrated into a single number that indicates the balance between atherogenic and antiatherogenic particles.

There have been many studies concerning the predictive power of the ApoB/ApoA1 ratio. One study, which involved thousands of patients who were followed for an average of 10 years, showed that the ApoB/ApoA1 ratio was a strong predictor of stroke in addition to other cardiovascular events. Due to the evidence presented in studies like these, the National Academy of Clinical Biochemistry (NACB) has recommended that the ApoB/ApoA1 ratio be used as an alternative to the usual total cholesterol (TC)/HDL cholesterol ratio when determining lipoprotein-related risk for cardiovascular disease. Some believe that ApoB/ApoA1 testing will eventually replace traditional LDL-C and HDL-C measurements. Another advantage is that the ApoB and ApoA1 tests are cheaper and less complex than most detergent-based cholesterol assays. So why hasn't this test replaced LDL-C and HDL-C in the US? The reason is that all or our practice guidelines, medication doses, screening recommendations and insurance reimbursements are based on decades of experience with LDL-C and HDL-C measurements. Cholesterol management, patient education and decades of established treatment algorithms represent a very large ship; it is no small thing to turn a ship that large.