Interpreting labs in dyslipidemia and cardiovascular disease
Understand the common primary and secondary causes of dyslipidemia and how to tell them apart.
Differentiating between primary and secondary causes of dyslipidemia, in order to assess cardiovascular risk, is crucial to optimal patient management. In this video, from our Cardiology Lab Essentials course, we'll cover the common primary and secondary causes of dyslipidemia, their prevalence, and how to tell them apart based on clinical findings, genetic testing, and lab test results.
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[00:00:00] When your patient's lab report shows pathologic lipid and lipoprotein values, you should be aware of the differentials that could cause these abnormalities. So, what are some causes of dyslipidemia? We can begin by distinguishing between primary and secondary causes. Primary dyslipidemias are inherited or familial disorders. These can be caused by mutations in a single gene, which we call monogenic
[00:00:30] or they may result from mutations in two or more genes, which we call polygenic disorders. Let's look first at monogenic lipid disorders. The most prevalent monogenic lipid disorder is familial hypercholesterolemia, which is very common in its heterozygous form and affects about 1 in 200 to 300 individuals in Europe and the US. The functional mutation lies within one of several genes involved in LDL metabolism and affects the removal of LDL from the blood.
[00:01:00] This disorder is characterized by a higher risk for cardiovascular events than in the general population, especially before the age of 40. In the lab report, you will find extremely elevated LDL cholesterol levels usually above 190 mg / dL or 4.9 mmoL / L but HDL cholesterol and triglycerides will often be normal. However, if the patient has other risk factors such as obesity or
[00:01:30] diabetes, elevations in triglycerides may be present and do not rule out familial hypercholesterolemia. The extreme elevation of LDL, especially at an early age, should make you suspicious that your patient may have familial hypercholesterolemia. Clinically, cholesterol depositions in skin, tendons, and arteries are characteristic of this disorder. The depositions in skin and tendons are called xanthoma. When clinical findings and lab results
[00:02:00] suggest familial hypercholesterolemia, genetic testing may not contribute substantially to the diagnosis, as it's generally not needed. Genetic testing is more important in asymptomatic patients with a positive family history. However, the need for genetic testing should be discussed with a lipid specialist. There are a variety of polygenic lipid disorders. Polygenic hypercholesterolemia is very common. It can be hard to distinguish from monogenic familial hypercholesterolemia
[00:02:30] but characteristic xanthomas are usually missing. The genes that cause polygenic hypercholesterolemia are currently not entirely known, so the disorder is diagnosed based on clinical presentation and family history. Another common polygenic inherited lipid disorder is familial combined hyperlipidemia. Lipid abnormalities can vary, with patients showing elevated total and LDL cholesterol, elevated triglycerides or both.
[00:03:00] In almost all cases, apolipoprotein B levels are also increased. Clinical signs like xanthomas are usually missing but the incidence of cardiovascular disease is high. Genetic mutations that are responsible for this disease are still unknown so patients are normally diagnosed based on clinical presentation and family history. These are a few of the most common inherited genetic disorders that could increase your patient's risk of dyslipidemia, however,
[00:03:30] not everyone with the genetic predisposition is doomed to have dyslipidemia and cardiovascular disease. What often pulls the trigger is our lifestyle. An unhealthy diet combined with significant lack of physical activity is just perfect for our lipids to get out of hand. The good news, we can intervene by changing our lifestyle habits for the better. In contrast to primary dyslipidemia, which is inherited and genetic, secondary dyslipidemia develops as the result
[00:04:00] of the presence of another pathology. Secondary causes of dyslipidemia are not as common as primary ones, however, about one-quarter of patients referred to a lipid clinic will have one or more secondary causes to be dealt with. Common causes of secondary dyslipidemia include hypothyroidism, diabetes with characteristically high triglycerides, low HDL cholesterol and elevated LDL cholesterol, obesity with similar abnormalities, excessive
[00:04:30] alcohol consumption leading to elevated triglyceride levels, renal disorders like nephrotic syndrome or chronic renal failure, cholestatic liver disorders like primary biliary cholangitis, and the chronic use of drugs like steroids, beta- blockers, thiazide diuretics or anticonvulsants. Secondary causes of dyslipidemia that especially concern women include the use of oral estrogens, polycystic ovary syndrome, and transiently, pregnancy.
[00:05:00] Acute and transient secondary causes of dyslipidemia may also include acute trauma, surgery, burns or severe peculiar and viral infections. In these situations, it might be better to postpone lipid screening if clinically feasible. As you can see there are many reasons why a patient might show lipid abnormalities. The important thing is to check for treatable causes then to establish your patient's cardiovascular risk and act on it.