Understanding the Essentials of Blood Lipid Metabolism

Kori J. Kingsbury, RN, MSN, Greg Bondy, MD, FRCPC

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In This Article

The Pathology of Dyslipidemia

"Dyslipidemia" refers to an abnormality within the lipid profile, encompassing a variety of disorders relating to elevations in total cholesterol, LDL, or TG, or conversely, lower levels of HDL. The dyslipidemia may present as a single disorder affecting only one lipoprotein parameter, or may represent a combination of lipoprotein abnormalities, such as elevated TG and low HDL.

A dyslipidemia may be the result of over-production or lack of clearance of the lipoprotein particles, or related to other defects in the apolipoproteins or enzyme deficiencies. The pathways and means of lipid metabolism in the human body reflect complex processes, and genetics, certain medical conditions, medications, and/or environmental factors may influence lipoprotein metabolism in some capacity, resulting in a dyslipidemic condition. In the clinical setting, a primary dyslipidemia typically refers to a genetic defect in the lipid metabolism as a cause of the problem. For example, familial hypercholesterolemia is a cause of primary dyslipidemia. It is characterized by a genetic mutation, resulting in impaired clearance of LDL from the circulation due to a lack of LDL receptors. The frequency of heterozygous familial hypercholesterolemia is about 1 in 500; homozygous familial hypercholesterolemia occurs in approximately 1 in 1 million.[23] In familial hypercholesterolemia patients, levels of LDL are significantly elevated, perhaps even at birth, and the impaired clearance of LDL frequently results in superfluous deposition of cholesterol in the arteries, skin, tendons, and corneas. A secondary dyslipidemia may be attributed to another cause. For example, environmental factors (such as a diet rich in saturated fat or a sedentary lifestyle), diseases (such as diabetes, hypothyroidism, obstructive liver disease), and medications (such as thiazide diuretics, progestins, or anabolic steroids) may result in a secondary dyslipidemia, which could be potentially resolved by correcting the underlying condition. In the clinical setting, a complete history and physical exam is key to assisting the clinician in establishing a dyslipidemia diagnosis and template for treatment. National guidelines recently published in Canada and the United States address risk stratification and intervention based on individual lipid profiles and risk factors.[5,6]

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