Vitamin B₁₂ (cyanocobalamin) and folic acid (pteroylglutamic acid) are essential for the production and maturation of erythrocytes. Both must be present for normal DNA replication and cell division. In humans, vitamin B₁₂ is obtained only by eating animal proteins, milk, and eggs, which places strict vegetarians at risk for developing cobalamin deficiency; hydrochloric acid (HCl) and intrinsic factor are required for absorption. Folic acid (or folate) is present in liver and in many foods of vegetable origin such as lima beans, kidney beans, and dark-green leafy vegetables. Note that canning and prolonged cooking destroy folate. Normally functioning intestinal mucosa is necessary for absorption of both vitamin B₁₂ and folic acid.

Vitamin B₁₂ is normally stored in the liver in sufficient quantity to withstand 1 year of zero intake. In contrast, most of the folic acid absorbed goes directly to the tissues, with a smaller amount stored in the liver. Folate stores are adequate for only 2 to 4 months.

• Determination of the cause of megaloblastic anemia:
  • Diagnosis of pernicious anemia, a megaloblastic anemia characterized by vitamin B₁₂ deficiency despite normal dietary intake
  • Diagnosis of megaloblastic anemia caused by deficient folic acid intake or increased folate requirements (e.g., in pregnancy and hemolytic anemias) or both, as indicated by decreased serum levels of folic acid
• Monitoring response to disorders that may lead to vitamin B₁₂ deficiency (e.g., gastric surgery, age-related atrophy of the gastric mucosa, surgical resection of the ileum, intestinal parasites, overgrowth of intestinal bacteria)
• Monitoring response to disorders that may lead to folate deficiency (e.g., disease of the small intestine, sprue, cirrhosis, chronic alcoholism, uremia, some malignancies)¹⁸
• Monitoring effects of drugs that are folic acid antagonists (e.g., alcohol, anticonvulsants, antimalarials, and certain drugs used to treat leukemia)¹⁹
• Monitoring effects of prolonged parenteral nutrition

Nursing Care Before the Procedure

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

• Samples should be drawn after the client has fasted for 8 hours and before injections of vitamin B₁₂ have been given.
• Alcohol also should be avoided for 24 hours before the test.

A venipuncture is performed and the sample collected in a red-topped tube. A capillary sample may be obtained in infants and children as well as in adults for whom venipuncture may not be feasible.

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 (see Appendix I).

• Foods and drugs withheld before the test may be resumed after the sample is obtained.
• Complications and precautions (anemia): Note and report folic acid levels of less than 4 ng and a normal level of vitamin B₁₂, indicating folic acid anemia. Prepare to administer ordered oral replacement therapy of folic acid; dosage and duration depend on the cause of the deficiency. Perform nursing activities for vitamin B₁₂ deficiency as in pernicious anemia diagnosed by the Schilling test (see Chapter 20 - Nuclear Scan and Laboratory Studies).