Lipids are transported in the blood as lipoproteins—complex molecules consisting of triglycerides, cholesterol, phospholipids, and proteins. Lipoproteins exist in several forms that reflect the different concentrations of their constituents. These forms, or fractions, are classified according to either their densities or their electrophoretic mobility.

The lipoprotein fractions in relation to density are (1) chylomicrons, (2) very-low-density lipoproteins (VLDL), (3) low-density lipoproteins (LDL), and (4) high-density lipoproteins (HDL). The least dense lipoproteins—chylomicrons and VLDL—contain the highest levels of triglycerides and lower amounts of cholesterol and protein. LDL and HDL contain the lowest amounts of triglycerides and relatively higher amounts of cholesterol and protein (see Table 5-10).

Lipoprotein densities correspond to the electrophoretic mobility patterns of the several lipo-protein fractions. The two main fractions of lipoproteins, as identified by electrophoresis, are and . -Lipoproteins, which approximate the HDL (₁), migrate with the -globulins. The -lipoproteins, which reflect the VLDL (pre-) and the LDL (), migrate with the -globulins. Chylomicrons remain at the origin.

The cholesterol content of the HDL and LDL fractions also can be determined by measuring total cholesterol remaining after one fraction has been removed. Note, however, that HDL cholesterol does not correlate well with the total cholesterol concentration, is higher in women than in men, and tends to be inversely proportional to triglyceride levels. High HDL cholesterol and low LDL cholesterol levels are predictive of a reduced risk of cardiovascular disease, whereas high LDL cholesterol and low HDL cholesterol levels are considered risk factors for atherosclerotic cardiovascular disease. Further, many health-care providers believe that an adequate lipid assessment need include only (1) total cholesterol, (2) HDL cholesterol, (3) serum triglycerides, and (4) estimate of chylomicron concentration.

Specific conditions associated with altered levels of lipoprotein fractions are listed in Table 5-14.

	Conventional Units	SI Units
Total lipoproteins	400-800 mg/dL	–
Chylomicrons	–	–
VLDL or pre-	3-32 mg/dL	–
LDL or	38-40 mg/dL	0.98-1.04 mmol/L
HDL or 1	20-48 mg/dL	0.51-1.24 mmol/L

Note: HDL cholesterol values are normally lower in men than in women, with an average range of 22 to 68 mg/dL.

• Failure to follow usual diet for 2 weeks before the test may yield results that do not accurately reflect client status.
• Ingestion of alcohol 24 hours before and food 12 hours before the test may alter results.
• Excessive exercise 12 hours before the test may alter results (regular exercise has been found to lower HDL cholesterol levels).
• Numerous drugs may alter results, including those that are known to alter lipoprotein components (see Tables 5-12 and 5-13).

• Serum cholesterol levels of greater than 250 mg/dL, which indicate high risk for cardiovascular disease and the need for further evaluation and possible treatment
• Estimation of the degree of risk for cardiovascular disease:
  • Individuals with LDL cholesterol levels greater than 160 mg/dL are considered to be at high risk.
  • Individuals at or above the upper reference range for HDL cholesterol have half the average risk, whereas those at or near the bottom have two, three, or more times the average risk.
• Known or suspected disorders associated with altered lipoprotein levels (see Table 5-14)
• Evaluation of response to treatment for altered levels and support for decisions regarding the need for drug therapy (LDL cholesterol levels may decrease with dietary modification alone; if not, drug treatment is recommended.)

Nursing Care Before the Procedure

General client preparation is the same as that for any procedure involving collection of a peripheral blood sample (see Appendix I).

• For this test, the client should ingest a normal diet, such that no weight gain or loss will occur for 2 weeks before the study, and should abstain from alcohol for 24 hours and from food for 12 hours before the test.
• Water is not restricted.
• The client also should avoid excessive exercise for at least 12 hours before the test.
• It also is recommended that drugs that may alter lipoprotein components be withheld for 24 to 48 hours before the test (see Tables 5-12 and 5-13), although this practice should be confirmed with the person ordering the study.

A venipuncture is performed and the sample collected in a red-topped tube. The sample should be sent promptly to the laboratory.

Nursing Care After the Procedure

Care and assessment after the procedure are the same as for any study involving the collection of a peripheral blood sample.

• Resume food and any drugs withheld before the test, as well as usual activities.
• Abnormal values: Note and report increased or decreased levels indicating atherosclerosis and high risk for heart disease. Administer ordered medications. Provide information about a low-fat, low-cholesterol, and low-calorie diet, if needed.