When we think of heart health, we often think about diet and how we can lower our cholesterol. For our patients, assessing their lipid profile helps determine their risk for cardiovascular disease. The lipid profile also helps to identify patients at risk for familial hypercholesterolemia, identify potential causes of pancreatitis, manage patients with atherosclerotic cardiovascular disease (ASCVD), and evaluate the effectiveness or compliance with lipid-lowering therapy and lifestyle modification (Sandeep, 2020). Let’s take a closer look at the lipid components in our blood.
There are five major lipoproteins in our blood: chlomicrons, very low-density lipoprotein (VLDL); intermediate-density lipoprotein (IDL); low-density lipoprotein (LDL), and high-density lipoprotein (HDL) (Rosenson, 2020). Each carries varying amounts of cholesterol and triglycerides. LDL carries most of the cholesterol and VLDL carries the majority of triglycerides. A typical blood lipid profile measures total cholesterol, HDL cholesterol and triglycerides. The LDL cholesterol is then estimated from these values.
The target range for cholesterol levels are (Centers for Disease Control and Prevention [CDC], 2020):
| Lipid Profile |
Normal Range |
| Total cholesterol |
< 200 mg/dL |
| LDL (“bad”) cholesterol [LDL-C] |
< 100 mg/dL |
| HDL (“good”) cholesterol [HDL-C] |
≥ 60 mg/dL |
| Triglycerides [TG] |
< 150 mg/dL |
LDL-C
LDL-C, or “bad” cholesterol, at high levels, can build up in the arteries and increase a person’s risk for heart attack, stroke, and peripheral artery disease (American Heart Association [AHA], 2017). LDL-C is often calculated using the Friedewald equation, Martin/Hopkins method or by direct measurement if total triglyceride level is greater than 400 mg/dL.
Friedewald equation
LDL cholesterol = Total cholesterol – VLDL cholesterol – HDL cholesterol
There are several drawbacks to the Friedewald equation. It is an estimation as the VLDL cannot be measured directly. VLDL is calculated by dividing the total triglycerides by 5. All values must be obtained from a patient in the fasting state and the formula cannot be used if a patient’s total triglyceride level is greater than 400 mg/dL.
The
Martin/Hopkin equation has been cited as more accurate than the Friedewald equation in patients with an LDL-C levels less than 70 mg/dL and triglyceride level > 150 mg/dL (Ferraro et al., 2019). This equation utilizes one of 180 adaptable ratios based on a patient’s individualized non-HDL-C and triglyceride values instead of the fixed ratio of five VLDL to TG. These ratios range from 3.1 to 119 and provide better reliability. Another advantage of this equation is that it does not require the patient to fast prior to testing.
The most accurate measure of LDL-C utilizes
ultracentrifugation, however this process is complex and costly.
Direct measurement using LDL-C assays or chemical-based methods are not reliable or standardized and may be less accurate than the Friedewald equation (Ferraro et al., 2019).
Non-HDL-C
Measuring
Non-HDL-C provides another method to estimate risk from atherogenic lipoproteins, those that tend to form fatty plaques in the arteries. It is calculated by subtracting HDL-C from total cholesterol and includes all cholesterol present in lipoprotein particles that are considered atherogenic, including LDL-C, lipoprotein (a), IDL, and VLDL. This value is useful in people with low or normal LDL-C but elevated triglycerides (≥ 200 mg/dL) and low HDL-C. Non-HDL-C is also a sensitive screening test of dyslipidemia in children (de Ferranti & Newburger, 2020).
HDL-C
HDL-C is considered the “good” cholesterol because it carries LDL cholesterol away from the arteries to the liver to be broken down and eliminated from the body (AHA, 2017). Only about a third or a fourth of the total LDL is carried by HDL. A healthy HDL cholesterol level may help decrease the risk of heart attack and stroke while low levels of HDL increase these risks (AHA, 2017), however a causal relationship has not been established.
Triglycerides
A high
triglyceride level combined with a high LDL or low HDL may cause fat build up within the arteries, increasing the risk of heart attack and stroke (AHA, 2017). Triglyceride levels help identify patients with other metabolic disorders such as diabetes, steatosis, or non-alcoholic fatty liver disease. High levels of triglycerides are also associated with development of pancreatitis.
Screening
Children with one or more risk factors for premature cardiovascular disease (CVD) should undergo selective screening (de Ferranti & Newburger, 2020). Children without CVD risk factors should be screened for dyslipidemia twice: between ages 9 and 11 years and again between 17 and 21 years (de Ferranti & Newburger, 2020). Adults who were not screened as children, should have a lipid profile drawn when they begin seeing an adult primary care practitioner (Sandeep, 2020) and then repeated every five years. More frequent screening is recommended for patients with a family history of premature ASCVD or when multiple risk factors are present. Specific lipid-related, “risk-enhancing” clinical factors in borderline and intermediate ASCVD risk adults include:
- LDL-C ≥ 160 mg/dL or non-HDL-C ≥ 190 mg/L
- Fasting triglycerides ≥ 175 mg/dL
- Lp(a) ≥ 50 mg/dL
- apolipoprotein B > 130 mg/dL
For more information on how lipids impact ASCVD risk and to learn about statin treatment recommendations, check out our blog summarizing the
guidelines on the primary prevention of cardiovascular disease. Advise your patients to eat a
heart healthy diet and exercise regularly to maintain a
normal weight in order to minimize their risk for ASCVD.
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