LDL Cholesterol: Reference Range, Interpretation, Collection and Panels

Sections

Reference Range

Normal blood test findings for low-density lipoprotein cholesterol (LDL-C) are as follows^[1]:

Adult - < 130 mg/dL
Children - < 110 mg/dL

Interpretation

LDL-C is one of the major culprits in the development of atherosclerotic heart disease.^[2]

Goal LDL (to prevent atherosclerotic plaque formation) is between 50-70 mg/dL. A higher value confers increasing risk for the development of coronary artery disease and needs to be remedied.^[3]This is based on The Framingham Heart Study, which was the first study to reveal a positive association between total cholesterol and coronary artery disease (CAD).^[4]

Achieving the LDL value of less than 100 mg/dL is especially important in patients who have other risk factors that will accelerate the development of CAD. These risk factors are cigarette smoking, hypertension, low high-density lipoprotein (HDL), and a family history of CAD.

In examining information from over 4200 adults with atherosclerotic cardiovascular disease (ASCVD), as culled from the National Health and Nutrition Examination Survey (NHANES) database, Vega and Grundy found what they described as a probable association between increased statin use and decreased levels of LDL-C. According to the study, between 1999-2000 and 2013-2014, LDL-C levels in the cohort fell by 24%, while the use of cholesterol-lowering drugs increased from 37% in 1999-2000 to 69% in 2015-2016.^[5]

A literature review by Schoeneck and Iggman indicated that certain foods affect LDL-C levels. For example, at least moderate reductions (0.2-0.4 mmol/L) in LDL-C were seen in correlation with foods that were high in unsaturated fatty acids and low in saturated and trans-fatty acids, as well as those with added plant sterols/stanols and foods with a high soluble fiber content. Small reductions (< 0.2 mmol/L) were associated with soy protein, tomatoes, flaxseeds, and almonds, while a moderate to large increase was attributed to the consumption of unfiltered coffee.^[6]

Collection and Panels

LDL-C is a calculated value and is part of the lipid profile recommended by the Adult Treatment Panel (ATP) III of the National Cholesterol Education Program (2001).

Blood is drawn after a 9-hour to 12-hour fast. The rationale behind fasting is to eliminate chylomicrons in the blood. If a patient doesn’t fast, it can cause an underestimation of the LDL value.

The sample is usually drawn in either a red-top or green- top tube and is part of the lipid profile. Early morning specimens are preferable. Patients should have been on a stable diet for 3 weeks for the results to be accurate.

Also note that in cases of recent myocardial infarction or stroke, lipid levels may be lower than what they actually are, and they normalize in 12 weeks. Checking a lipid panel 12 weeks after the acute insult is wise.

Description

About 60-70% of cholesterol in the body is carried as low-density lipoprotein cholesterol (LDL-C) in the blood.

The standard lipid profile, as recommended by the ATP III, consists of direct measurement of total cholesterol, HDL-C, and triglycerides, with a calculated LDL-C, obtained after a 9-hour to 12-hour fast. The Friedewald formula used to calculate the LDL level in the blood is as follows:

LDL = Total cholesterol − HDL − (Triglycerides/5)

Lipoproteins are required for the transportation of cholesterol, which in turn is required for the biosynthesis of bile acids, steroid hormones, and vitamin D.

Two main sources of cholesterol exist: One is dietary intake and the other is endogenous hepatic production.

Metabolism of ingested cholesterol yields very–low-density lipoprotein (VLDL) and intermediate-density lipoprotein (IDL). Further metabolism of the VLDL results in the cholesterol rich LDL, which is the key ingredient for the development of an atherosclerotic plaque.