Phospholipids consist of one or more fatty acid molecules and one phosphoric acid radical, and they usually have a nitrogenous base. The three major types of body phospholipids are the lecithins, the cephalins, and the sphingomyelins. In addition to diet as a source of phospholipids, nearly all body cells are capable of forming these lipids. Most endogenous phospholipids are formed, however, in the liver and intestinal mucosa. The phospholipids are transported together in circulating blood in the form of lipoproteins.

Phospholipids are important for the formation of cell membranes and for the transportation of fatty acids through the intestinal mucosa into lymph. Phospholipids also serve as donors of phosphate groups for intracellular metabolic processes and may act as carriers in active transport systems. Saturated lecithins are essential for pulmonary gas exchange, whereas the cephalins are major constituents of thromboplastin, which is necessary to initiate the clotting process. Sphingomyelin is present in large quantities in the nervous system and acts as an insulator around nerve fibers.²⁴

Phospholipids may be measured as part of an overall lipid evaluation, but the significance of altered levels is not completely understood. A direct relationship between elevated phospholipids and atherosclerotic cardiovascular disease has not been demonstrated.

Alterations in phospholipid levels may be seen in situations similar to those in which serum triglycerides and cholesterol also are abnormal. For example, elevated levels are associated with diabetes mellitus, nephrotic syndrome, chronic pancreatitis, obstructive jaundice, and early starvation. Decreased levels are seen in clients with primary hypolipoproteinemia, severe malnutrition and malabsorption syndromes, and cirrhosis. Antilipemic drugs (e.g., clofibrate) may lower phospholipid levels, and epinephrine, estrogens, and chlorpromazine tend to elevate them.

Another clinical application of phospholipid data is the use of the lecithin:sphingomyelin (L:S) ratio in estimating fetal lung maturity, with adequate lung maturity indicated by lecithin levels greater than those for sphingomyelin by a ratio of 2:1 or greater (see Chapter 10 - Amniotic Fluid Analysis).

Note: Values may vary, depending on the laboratory performing the test and the age of the client.

• Ingestion of alcohol 24 hours before and food 12 hours before the test may falsely elevate levels.
• Ingestion of drugs known to alter phospholipid levels within 12 hours before the test may alter results unless the test is being conducted to evaluate such effects.
• Antilipemic drugs (e.g., clofibrate) may lower phospholipid levels.
• Epinephrine, estrogens, and chlorpromazine tend to elevate phospholipid levels.

• Known or suspected disorders that cause or are associated with altered lipid metabolism:
  • Altered phospholipid levels are seen in situations similar to those in which serum triglycerides and cholesterol also are altered (see Tables 5-12 and 5-13).
  • Elevated levels are associated with diabetes mellitus, nephrotic syndrome, chronic pancreatitis, obstructive jaundice, and early starvation.
  • Decreased levels are seen in primary hypolipoproteinemia, severe malnutrition, malabsorption syndromes, and cirrhosis.
• Support for identifying problems related to fat metabolism and transport:
  • Phospholipid formation parallels deposition of triglycerides in the liver, and severely decreased levels result in low levels of lipoproteins that are essential for fat transport.
• Abnormal bleeding of unknown origin, with decreased cephalin (a type of phospholipid), a possible contributor to low levels of thromboplastin
• Suspected neurological disorder, which may be associated with decreased levels of sphingomyelin (a type of phospholipid)

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 abstain from alcohol for 24 hours and from food for 12 hours before the study.
• Water is not restricted.
• It also is recommended that drugs that may alter phospholipid levels be withheld for 12 hours before the test, 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 foods and any drugs withheld before the test.