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Test ID: LDLD    
LDL Cholesterol (Beta-Quantification), Serum

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Useful For Suggests clinical disorders or settings where the test may be helpful

Evaluation of cardiovascular risk

 

Assessment of low-density lipoprotein C (LDL-C) in patients with hypertriglyceridemia, type III hyperlipoproteinemia/dysbetalipoproteinemia, high concentrations of lipoprotein(a), or intermediate-density lipoprotein, and/or when an accurate gold standard determination of LDL-C is required.

 

Diagnosis of abetalipoproteinemia

 

Diagnosis of hypobetalipoproteinemia

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Low-density lipoprotein cholesterol (LDL-C) is widely recognized as an established cardiovascular risk marker predicated on results from numerous clinical trials that demonstrate the ability of LDL-C to independently predict development and progression of coronary heart disease. In the United States, LDL-C remains the primary focus for cardiovascular risk assessment and evaluation of pharmacologic effectiveness based on treatment target goals. There have been considerable educational efforts invested and directed towards physicians, laboratorians, allied health staff, and the general public regarding LDL-C and strategies to lower LDL-C for reduction of cardiovascular risk.

 

Low-density lipoproteins are a heterogeneous population of lipid particles classically defined as having a density of 1.006 to 1.063 kg/L obtained by preparative ultracentrifugation. The gold standard beta-quantification (beta-quant or BQ) method combines ultracentrifugation with precipitation and yields a collective quantitative measurement of LDL-C, intermediate-density lipoprotein cholesterol (IDL-C), and lipoprotein(a) cholesterol (Lp(a)-C). In practice, LDL-C is most commonly reported using the Friedewald equation (LDL-C=TC-HDL-TG/5), which yields a fair estimation of LDL-C compared to beta-quantification.

 

Importantly, there are significant shortcomings and limitations to the Friedewald equation, particularly with the accuracy which require multiple fasting samples to be tested prior to initiation or modification of therapy and recommendations against reporting a calculated LDL-C in patients who are nonfasting, have triglycerides greater than 400 mg/dL, or have type III hyperlipoproteinemia. The equation is particularly inaccurate once the triglycerides are above 200 mg/dL or at low LDL-C concentrations. Furthermore, beta-quantification is an effective method for removal of triglyceride-rich very low- density lipoprotein (VLDL) particles and chylomicrons which often interfere with routine measurement of high-density lipoprotein cholesterol (HDL-C) and calculation of LDL-C.

 

Homogenous or "direct" LDL-C assays were designed to circumvent the issues with calculating LDL-C in specimens with triglycerides over 400 mg/dL. Clinical laboratories may utilize direct LDL-C assays for that purpose, however recent studies clearly indicate these methods, like lower calculated LDL-C, are unable to adhere to the National Cholesterol Education Program (NCEP) total error goal of <12% for LDL-C and are particularly unsuitable for use in a dyslipidemic population.

 

There are 2 genetic disorders which cause low LDL-C concentrations, termed abetalipoproteinemia and hypobetalipoproteinemia, and are collectively referred to as familial hypobetalipoproteinemia. Abetalipoproteinemia is a rare recessive disorder caused by a mutation in the MTP gene which encodes for microsomal triglyceride transfer protein. Mutations in MTP result in apolipoprotein B-48 and B-100 deficiencies, which cause impaired absorption of dietary lipids, lipoproteins, and cholesterol in the intestines and a variety of vitamin deficiencies. Individuals will have very low total cholesterol and diminished or absent LDL-C, apolipoprotein B (apoB) and very low-density lipoprotein cholesterol (VLDL-C).  Abetalipoproteinemia may be a cause of polyneuropathy.

 

Hypobetalipoproteinemia is associated with mutations occurring at a variety of genetic loci but primarily involve mutations in the apoB gene. Individuals with hypobetalipoproteinemia exhibit clinical signs and symptoms of intestinal fat malabsorption, hepatosteatosis, and fat soluble vitamin deficiencies although the severity of their symptoms is much less than individuals with abetalipoproteinemia. Patients with hypobetalipoproteinemia have very low concentrations of plasma apoB and LDL-C (<fifth percentile of age- and sex-specific values; LDL-C levels between 25 and 40 mg/dL), as well as decreased VLDL-C concentrations. 

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

The National Cholesterol Education Program (NCEP) has set the following guidelines for LDL-C in adults (ages 18 years and up):

Optimal: <100 mg/dL*

Near optimal: 100-129 mg/dL

Borderline high: 130-159 mg/dL

High: 160-189 mg/dL

Very high: > or =190 mg/dL

*In patients with a history of heart disease and/or diabetes an LDL-C goal of <70 mg/dL should be considered

 

The National Cholesterol Education Program (NCEP) has set the following guidelines for LDL-C in children and adolescents (ages 2-17 years):

Desirable: <110 mg/dL

Borderline high: 110-129 mg/dL

High: > or =130 mg/dL

Interpretation Provides information to assist in interpretation of the test results

Evaluation of low-density lipoprotein cholesterol (LDL-C)-related cardiovascular risk is based on the following range of values established by the National Cholesterol Education Program (NCEP) in adults (ages 18 years and up):

 

Optimal: <100 mg/dL*

Near optimal: 100-129 mg/dL

Borderline high: 130-159 mg/dL

High: 160-189 mg/dL

Very high: > or =190 mg/dL

*In patients with a history of heart disease and/or diabetes an LDL-C goal of <70 mg/dL should be considered

 

The NCEP has set the following guidelines for LDL-C in children and adolescents (ages 2-17 years):

Acceptable: <110 mg/dL

Borderline high: 110-129 mg/dL

High: > or =130 mg/dL

 

Decreased values may indicate hypobetalipoproteinemia.

 

Undetectable LDL-C is highly suggestive of abetalipoproteinemia. Related polyneuropathy may exist in affected individuals.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Patients should fast for 12 to 14 hours before the blood is drawn. The patient can take water and prescription drugs if necessary. Alcohol should be avoided for at least 24 hours before specimen draw.

Clinical Reference Provides recommendations for further in-depth reading of a clinical nature

Executive Summary of the Third Report of the National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III), JAMA 2001;285:2486-2497