Lipoprotein Metabolism Profile
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Levels of total cholesterol and triglycerides are dependent on age, sex, diet, physical activity profile, and the presence or absence of inheritable and nonheritable metabolic problems. Abnormalities in the serum lipoprotein profile can suggest various problems in metabolism, liver function, and renal function, in addition to being reflections of problems in lipid transport.
Increased levels of low-density lipoprotein (LDL) and cholesterol-rich, small-particle, very low-density lipoprotein (VLDL), which are seen in type III hyperlipoproteinemia, are risk factors for atherosclerotic disease. Increased high-density lipoprotein (HDL) levels are considered favorable in relation to atherosclerotic disease.
While serum total cholesterol and HDL cholesterol values may be adequate for evaluation of some patients, for many patients an adequate evaluation can be accomplished only with examination of the entire lipoprotein profile. Analysis of serum lipoproteins may be of use if the patient's cholesterol, triglycerides, HDL, or LDL are abnormal (ie, outside the guidelines established by the National Cholesterol Education Program). In these patients, measurement of only total cholesterol or triglycerides does not provide sufficient information and may be misleading.
Care must be taken in the interpretation of apparent hypercholesterolemia (increased total cholesterol), since it can reflect an increased LDL with an increased risk for atherosclerotic disease, or a high level of HDL with a reduced risk. While hypercholesterolemia is often considered to be an expression of an increased concentration of LDL (type IIa hyperlipoproteinemia), in some patients increased total cholesterol levels reflect increased levels of other lipoproteins (eg, HDL, VLDL, or chylomicrons). In addition, hypercholesterolemia can reflect the presence of "LP-X," the abnormal lipoprotein complex associated with cholestasis or anomalous conditions. Hypercholesterolemia can best be identified through the combination of electrophoretic screening and quantitative testing, with the quantitative method determined by the forms of lipoproteins that are prominent in the electrophoretogram.
Identification of patients with type III hyperlipoproteinemia may be helpful for optimal patient management; analysis of VLDL particles is necessary to identify these patients. VLDL and HDL contain varying amounts of cholesterol, triglycerides, and phospholipids; the cholesterol and triglyceride content in these fractions has clinical significance. A definitive analysis must include establishing the presence of an increased population of cholesterol-rich VLDL particles of sizes that are much smaller than the primary VLDL particles; evaluation of the cholesterol:triglyceride ratio in the isolated total VLDL fraction is a necessary step in diagnosis.
A high level of HDL may or may not reflect a healthy status. In a person free of liver disease or intoxication of any form, a high level of HDL is an indication of a healthy metabolic system and probably indicates a relatively low risk for atherosclerotic disease. Otherwise, a high level of HDL may reflect the existence of an early stage of primary biliary cirrhosis, chronic hepatitis, alcoholism, or some other form of chronic intoxication. This interpretational problem is readily resolvable through simple quantitative testing involving ultracentrifugation, selective precipitation, or a combination of these methods.
Classifying the hyperlipoproteinemias into phenotypes has limited value for the evaluation of genetic traits, but does place disorders that affect plasma lipid and lipoprotein concentrations into convenient groups for evaluation and treatment. A clear distinction must be made between primary (inherited) and secondary (liver disease, alcoholism, metabolic diseases) causes of dyslipoproteinemia.
Determining the existence and type of dyslipoproteinemia
Quantitation of cholesterol and triglycerides in VLDL, LDL, HDL, Lp(a), and any other significant lipoprotein fractions
Classifying hyperlipoproteinemias (lipoprotein phenotyping)
Evaluating patients with abnormal lipid values (cholesterol, triglyceride, HDL, LDL)
Quantifying Lp(a) cholesterol
For discussion of various lipoprotein fractions, see Clinical Information.
For a discussion of Lp(a), see LPAWS / Lipoprotein (a) Cholesterol, Serum
For treatment recommendations, see Lipids and Lipoproteins in Blood Plasma (Serum), National Cholesterol Education Program Guidelines, in Special Instructions.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Reference values are based on fasting collections; it is essential that the patient fasts 12 to 14 hours before the test.
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 lipids (total cholesterol, triglycerides, HDL, and LDL cholesterol) in adults ages 18 and up:
Desirable: <200 mg/dL
Borderline high: 200-239 mg/dL
High: > or =240 mg/dL
Normal: <150 mg/dL
Borderline high: 150-199 mg/dL
High: 200-499 mg/dL
Very high: > or =500 mg/dL
Low: <40 mg/dL
Normal: 40-59 mg/dL
High: > or =60 mg/dL
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
The National Cholesterol Education Program (NCEP) and National Health and Nutrition Examination Survey (NHANES) have set the following guidelines for lipids (total cholesterol, triglycerides, HDL, and LDL cholesterol) in children ages 2-17:
Desirable: <170 mg/dL
Borderline high: 170-199 mg/dL
High: > or =200 mg/dL
Normal: <90 mg/dL
Borderline high: 90-129 mg/dL
High: > or =130 mg/dL
Low: <40 mg/dL
Borderline low: 40-59 mg/dL
Normal: > or =60 mg/dL
Desirable: <110 mg/dL
Borderline high: 110-129 mg/dL
High: > or =130 mg/dL
Males and females > or =18 years: 48-124 mg/dL
Desirable: <3 mg/dL
Values > or =3 mg/dL may suggest increased risk of coronary artery disease.
Also see age- and sex-adjusted reference values in Lipid Reference Values for Lipoprotein Profile in Lipids and Lipoproteins in Blood Plasma (Serum) in Special Instructions.
Clinical References Provides recommendations for further in-depth reading of a clinical nature
1. Schriver CR, Beaudet AL, Sly WS, Valle D: Lipoprotein and lipid disorders. In The Metabolic Basis of Inherited Disease. Sixth edition. Edited by JB Stanbury, JB Wyngaarden, DS Frederickson. New York, McGraw-Hill Book Company, 1989, pp 1129-1302
2. Grinstead GF, Ellefson RD: Heterogeneity of lipoprotein Lp(a) and apolipoprotein(a). Clin Chem 1988;34:1036-1040