ADVANCED LIPID TESTING

Advanced lipid testing is a more comprehensive and detailed method of evaluating cardiovascular disease (CVD) risk compared to traditional lipid panel testing. Traditional lipid panel testing typically measures total cholesterol, low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), and triglycerides. While these tests are useful in assessing risk, they may not capture the full picture of an individual's lipid profile and CVD risk.

Advanced lipid testing aims to provide a better understanding of an individual's lipid profile by measuring additional markers that can help identify and manage high-risk individuals. These advanced tests can include:

1. Apolipoprotein B (ApoB): A protein found in LDL particles, ApoB is a more direct measure of the number of atherogenic (plaque-forming) particles in the blood. Higher levels of ApoB are associated with an increased risk of CVD.
2. Apolipoprotein A1 (ApoA1): A protein found in HDL particles, ApoA1 is a marker of the number and functionality of HDL particles. Higher levels of ApoA1 are generally associated with a lower risk of CVD.
3. ApoB/ApoA1 ratio: This ratio compares the levels of atherogenic (ApoB) and protective (ApoA1) particles, providing a more comprehensive assessment of CVD risk. A higher ratio indicates a greater risk of CVD.
4. Lipoprotein(a) [Lp(a)]: Lp(a) is a type of LDL particle with an additional protein called apolipoprotein(a). Elevated levels of Lp(a) are associated with an increased risk of CVD, especially in those with a family history of early heart disease.
5. LDL particle number (LDL-P): This test measures the actual number of LDL particles, rather than just the cholesterol contained within them. Elevated LDL-P levels are associated with an increased risk of CVD, even if the LDL-C levels are normal.
6. LDL particle size and subclasses: Some individuals have smaller, denser LDL particles that are more easily oxidized and can penetrate the arterial wall more easily, increasing the risk of plaque formation. Advanced lipid testing can measure the size and distribution of LDL particles, which can help in assessing an individual's CVD risk.
7. High-sensitivity C-reactive protein (hs-CRP): While not a lipid marker, hs-CRP is an inflammatory marker that can help predict the risk of CVD. Elevated hs-CRP levels are associated with an increased risk of heart disease and stroke.

Advanced lipid testing can be particularly useful for individuals with a family history of early heart disease, those with borderline or high traditional lipid levels, and individuals with other risk factors for CVD, such as diabetes, obesity, or a history of smoking. By providing a more detailed lipid profile, these tests can help healthcare providers better tailor treatment plans and preventive measures to reduce CVD risk.

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Advanced lipid testing refers to more comprehensive blood tests to assess your cardiovascular disease risk. Standard lipid panels only measure total cholesterol, LDL or "bad" cholesterol, HDL or "good" cholesterol, and triglycerides. Advanced lipid testing provides more details about the quality and quantity of lipids in your blood. It can help determine the best ways to reduce your risk of heart disease and monitor the effectiveness of treatment.

Some of the advanced lipid tests available include:

• Lipoprotein particle testing: Measures the number and size of LDL and HDL particles. Having more small, dense LDL particles increases heart disease risk even if your LDL cholesterol is normal. Larger HDL particles seem to offer more protection.
• Lp(a) testing: Measures lipoprotein(a) levels. Elevated Lp(a) is an independent risk factor for heart disease. Standard lipid panels do not check Lp(a). Lowering Lp(a) often requires medication beyond just diet and lifestyle changes.
• Apolipoprotein testing: Measures the levels of apolipoproteins like apoB and the apoB/apoA1 ratio. Apolipoproteins are proteins that carry cholesterol and triglycerides in your blood. High apoB and a high apoB/apoA1 ratio signify increased plaque buildup in the arteries.
• Triglyceride/HDL ratio: Provides an assessment of insulin resistance and cardiovascular risk. A ratio less than 2 is ideal, while 3-4 signifies increased risk and over 5 is high risk. Lifestyle changes and medication can help lower a high ratio.
• Non-HDL cholesterol testing: Measures total cholesterol minus your HDL. This includes all the pro-atherogenic lipoproteins like LDL, Lp(a), and triglyceride remnants. A high non-HDL cholesterol level is a strong predictor of cardiovascular disease, especially if over 130 mg/dL.
• VLDL cholesterol testing: Measures very low-density lipoprotein (VLDL) which carries triglycerides. High VLDL is a risk factor for atherosclerosis and often linked to insulin resistance and metabolic syndrome. Lifestyle interventions and medication like statins or fibrates may be needed to lower high VLDL.
• Oxidized LDL testing: Measures the level of oxidized LDL particles which are more harmful than normal LDL. While still largely a research tool, oxidized LDL may identify people at higher risk even with normal LDL levels. Antioxidants and other strategies can help lower oxidized LDL.

Advanced lipid testing is often ordered when standard cholesterol tests do not fully assess someone's risk, or when heart disease is suspected despite normal or only mildly abnormal cholesterol levels. The results can guide treatment and help reduce the risk of cardiovascular events. Discuss advanced lipid testing options with your doctor if you have concerns about your heart health.

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Topic Highlights:-

• Cardiovascular risk factors extend beyond cholesterol to include small proteins and lipoprotein subtypes.
• Cardiovascular risk is better assessed by identifying measurable lipid risk factors using newer techniques.
• The kinds of lipids and their functions, the risk factors associated with abnormal lipid levels, the advanced lipid testing methods, and the role of these methods in clinical assessment are discussed in detail in this presentation.

Transcript:-
Lipid-related cardiovascular risk factors include not only cholesterol but also lipoproteins and their subtypes. Cardiovascular risk is best assessed by identifying measurable lipid risk factors. Advanced lipid testing, therefore, plays a crucial role in clinical practice. This presentation discusses in detail the kinds of lipids and their functions, the risk factors associated with abnormal levels of lipids, and the role of advanced lipid testing in clinical assessment.

Atherosclerotic cardiovascular disease (CVD) is a major cause of mortality and morbidity. Its main acute clinical manifestations are myocardial infarction and stroke. The treatment of risk factors is the most important, urgent, and effective way to prevent these diseases. Various forms of dyslipidemia (disorders of blood lipids) are important causative risk factors for atherosclerotic CVD. Other significant risk factors that are easily determined in clinical practice are smoking, overweight/obesity, hypertension, and diabetes.

Lipid testing is used here in the context of “determination of lipids in blood for the evaluation of a person’s cardiovascular risk status.” Lipid testing began early in the 20th century when the Lieberman–Burchard reaction for cholesterol was devised, making it possible to determine the concentration of plasma cholesterol, which soon led to the discovery that plasma cholesterol is often high in patients with myocardial infarction. In the mid-1960s, the prospective Framingham study demonstrated that cholesterol is a risk factor for the development of coronary heart disease (CHD). Soon after, researchers realized that cholesterol and other lipids in the blood are bound to proteins called apolipoproteins (apo) and are part of large complexes called lipoproteins.

Classification of Lipoproteins Using physicochemical methods, plasma lipoproteins have been classified into three major groups:

• very low density lipoprotein (VLDL), estimated from triglyceride values
• low-density lipoprotein (LDL), measured as LDL cholesterol (LDL-C)
• high-density lipoprotein (HDL), measured as HDL cholesterol (HDL-C)

Of these groups, LDL carries a major part of plasma cholesterol and is the most atherogenic lipoprotein class; hence, LDL-C is called “the bad cholesterol.” In contrast, HDL-C protects against atherosclerosis and is hence called “the good cholesterol.” Therefore, both high levels of LDL-C and low levels of HDL-C are risk factors for CHD.

Lipid Profile Presently, most laboratories provide clinicians with the following lipid profile:

• total cholesterol
• triglycerides
• LDL-C
• HDL-C
• non-HDL-C
• ratios of LDL-C to HDL-C or LDL-C to total

In addition to this standard lipid profile, many laboratories also determine the major apo components of LDL, VLDL, and HDL:

• apo B
• apo A-I
• ratios of LDL-C to HDL-C or LDL-C to total

Apo B reflects the amount of LDL plus VLDL, and apo A-I indicates the amount of HDL. There is presently an ongoing discussion if the apo’s and their ratios are better predictors of CHD than the lipid profile. Advanced lipid testing measures the following:

• cholesterol content of the subclasses of the major lipoprotein classes
• size and number of lipoprotein particles in the various subclasses
• other lipoprotein species such as Lp(a)

Both LDL and HDL are heterogeneous lipoprotein classes consisting of lipoprotein particles varying in size, composition, and atherogenicity.

Small and dense LDL (sdLDL) particles, an LDL subclass, are more atherogenic than the larger, more buoyant LDL particles because they are smaller (penetrate easier into the arterial wall), more prone to modification by oxidation, and therefore more rapidly taken up by the scavenger receptors of the macrophages, which then turn into foam cells, a characteristic feature of atherosclerotic lesions. sdLDL is now recognized as a strong risk factor for CHD both in Western and Japanese populations. This observation is becoming more and more evident that it is important to pay attention not only to LDL-C, but also to sdLDL and its significance in the evaluation of a patient’s risk for CHD and in the prevention of CHD.

The protective HDL is also a heterogeneous lipoprotein class, the subclasses of which have been ascribed different atheroprotective potentials. Attention is directed toward the larger HDL, particularly the large HDL2 subclass, which appears to be the most protective HDL subclass. HDL2 is actively engaged in reverse cholesterol transport, the process by which cholesterol can be transported away from atherosclerotic lesions to the liver for excretion from the body via the bile. Lp(a) is a distinct genetic form of LDL that contains apo(a) in addition to apo B. Apo(a) has a structural similarity to plasminogen . Lp(a) is a strong risk factor for clinical atherosclerosis. Unlike LDL, Lp(a) does not respond to treatment with diet or statins. However, its concentration is markedly reduced by nicotinic acid.

Several methods are available for the determination of lipoprotein subclasses, and these methods are still mostly used in research or clinical trials. However, with the increasing awareness of the importance of various subclasses in the reverse cholesterol transport of atherosclerosis and as risk factors for CVD, these methods will undoubtedly be used more frequently in clinical practice. This development will be in response to clinicians’ demands to obtain more advanced lipid profiles in which lipoprotein subclasses are also determined. Since the groundbreaking work of John Gofman with analytical ultracentrifugation in the 1990s, human plasma lipoproteins have been well established as a very heterogeneous group of proteins or particles, greatly varying in size, density, and composition. The different characteristics of the subclasses have made it possible to separate and quantify these proteins or particles by physicochemical methods, such as electrophoresis and ultracentrifugation.

Polyacrylamide gradient gel electrophoresis has been used for 25 years as a practical method for the separation and analysis of lipoproteins of different sizes, such as HDL and LDL particles that vary in diameter (7–12 nm and 21–28 nm, respectively). Polyacrylamide gels have pores of decreasing size in the direction of the electrophoretic mobility, preventing lipoproteins of a certain size from moving further on in the gel in the electric field.

To analyze HDL subfractions, a gradient in the range of 4%–30% polyacrylamide concentration is used. With this technique, HDL is separated into five distinct subclasses.

To determine LDL subclasses, 2%–16% polyacrylamide gel is generally applied. Gradient gel electrophoresis of LDL has identified seven subclasses. There is, however, no standard nomenclature for these subclasses. At present, the most useful terms for LDL subclasses are the two phenotypes of LDL described by Austin. Phenotype A contains large LDL, while phenotype B consists of sdLDL. The determination of sdLDL is the most significant measurement of LDL subclasses for the evaluation of a person’s risk for CHD.

In ultracentrifugation, the density of lipoproteins is due to their lipid content; that is, the lipid/protein ratio determines the separation and identification of the various subclasses. Analytical ultracentrifugation is the standard for a quantification of lipoprotein classes, but it is too laborious and expensive for routine use. The recently developed SVAP method is a single vertical spin density gradient ultracentrifugation combined with cholesterol analysis of the separated lipoprotein classes. The advantages of SVAP are the use of small plasma samples, short centrifugation time, and determination of an advanced quantitative lipoprotein subclass spectrum.

The determination of plasma lipoprotein subclasses by nuclear magnetic resonance (NMR) spectroscopy started in the 1990s. A plasma sample is placed in the NMR analyzer, and a spectrum is recorded within a minute. By computer analysis of the spectrum, the amounts of large, medium, and small particle subclasses of VLDL, LDL, and HDL are estimated.

Studies of the subclasses of both LDL and HDL have revealed important clinical and metabolic differences between the subclasses. Several prospective epidemiological studies have shown that sdLDL is a very important risk factor for the development of atherosclerotic CVD. According to some studies, sdLDL is an even better indicator of CHD risk than LDL-C. For example, in a prospective Quebec study comprising more than 2000 men free of CHD, the subjects with high levels of sdLDL but normal concentrations of LDL-C had a fourfold increased risk for new events of CVD. High levels of sdLDL are common in hypertriglyceridemia, which is often present in type 2 diabetes and metabolic syndrome. The concentration of sdLDL can be reduced by lifestyle improvements and by pharmacological treatment with statins, nicotinic acid, and fibrates.

Both progression and severity of coronary atherosclerosis are inversely proportional to the large HDL2b subclass, which appears to have a more protective effect against atherosclerosis than other HDL subclasses. There is a pronounced difference in the distribution of HDL subclasses between men and women. Particularly noteworthy is that men have lower levels of protective HDL2, which partly explains the higher incidence of CHD in males than in females at a younger age. Fibrates and statins increase HDL-C by about 5%–20%, and nicotinic acid increases HDL-C by 20%–40%. The pharmacological treatment with statins, nicotinic acid, and fibrates also decreases the HDL2 subclass by about 100% and the HDL3 subclass by 20%, which further illustrates the importance of evaluating the subclasses of the major lipoprotein classes by advanced lipid testing.

Given the prevalence of CHD and CVD, tests to obtain detailed profiles of lipid subclasses are a necessity. Advanced lipid testing, though not recommended for routine screening, is important in identifying individuals at high risk of CHD or CVD, especially those with a family history of premature CHD, individuals with an intermediate risk for CHD, and postmenopausal women. These tests will facilitate early identification, more effective treatments, and an overall reduction in the occurrence of atherosclerotic CVD.