Vitamin A is obtained from foods of animal origin, such as eggs, milk, butter, and liver. Its precursor, carotene, a yellowish pigment, is obtained from yellow or orange vegetables and fruits and from leafy green vegetables.

Vitamin A promotes normal vision by permitting visual adaptation to light and dark, and it prevents night blindness (xerophthalmia). It also contributes to the growth of bone, teeth, and soft tissues; supports the formation of thyroxine; maintains epithelial cellular membranes; aids in spermatogenesis; and maintains the integrity of skin and mucous membranes as barriers to infection.

• Pregnancy and oral contraceptive use can lead to falsely elevated levels, as can hyperlipidemia, hypercholesterolemia of diabetes, myxedema, and nephritis.
• Excessive ingestion of mineral oil, low-fat diets, and liver disease may lead to decreased levels.
• Failure to follow dietary and drug restrictions before the test may alter results.
• Excessive exposure of the sample to light may alter results.

• Evaluation of skin disorders, with vitamin A deficiency a possible cause
• Support for diagnosing xerophthalmia (night blindness) as indicated by decreased levels
• Suspected vitamin A deficiency caused by fat malabsorption or biliary tract disease
• Support for diagnosing excessive vitamin A or carotene ingestion, or both, as indicated by elevated blood levels

Nursing Care Before the Procedure

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

• For this test, the client should fast for 8 hours before the study. Water is not restricted.
• Vitamin supplements containing vitamin A should be withheld for at least 24 hours before the test.

A venipuncture is performed and the sample collected in a red-topped tube. The sample should be covered to protect it from light, which may alter test results; handled gently to avoid hemolysis; and sent promptly to the laboratory.

Nursing Care After the Procedure

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

• Resume usual diet.
• Vitamin supplements may be resumed pending test results.
• Decreased level: Note and report symptoms of deficiency or decreased level. Administer ordered vitamin A supplement orally, and instruct client to eat foods high in vitamin A to correct deficiency.
• Increased level: Note and report symptoms of excesses or increased level. Discontinue the oral or topical medication administered for acne or other skin conditions.