A client with suspected vitamin B12 deficiency anemia has the following laboratory results: macrocytic (large), hypochromic (pale) RBCs with low hemoglobin (Hgb) and hematocrit (Hct) levels.
The mean corpuscular volume (MCV) is above 100 fL.
Which of the following laboratory tests would further confirm the diagnosis of vitamin B12 deficiency anemia?

Choice A rationale:

Following a strict vegan diet can lead to vitamin B12 deficiency as it is primarily found in animal products.

However, the patient's recent gastrectomy is a more likely cause of their condition.

Choice B rationale:

This is the correct answer.

A gastrectomy can interfere with the absorption of vitamin B12 in the stomach, leading to a deficiency.

Choice C rationale:

Regular use of acid-suppressing drugs may affect the absorption of some nutrients, including vitamin B12, but it is not as direct a cause as a gastrectomy.

Choice D rationale:

Family history of pernicious anemia indicates a genetic predisposition, but it may not be the direct cause in this case.

The gastrectomy is a more likely cause.

Choice A rationale:

Administering 500 mcg of cyanocobalamin intramuscularly daily for a week, then monthly for life is the appropriate route and dosage for a patient with pernicious anemia or severe malabsorption.

Intramuscular injection is the preferred route for patients with impaired absorption of vitamin B12, as it ensures direct absorption into the bloodstream.

The initial daily dose helps replenish depleted stores, and the monthly maintenance dose is required to prevent recurrence.

Choice B rationale:

Administering 1000 mcg of cyanocobalamin orally daily for a week, then weekly for a month, then monthly for life is not the best choice for patients with pernicious anemia or severe malabsorption.

Oral vitamin B12 is not effective in these cases because the underlying issue is the inability to absorb vitamin B12 from the gastrointestinal tract.

Intramuscular administration bypasses this problem.

Choice C rationale:

Administering 1000 mcg of cyanocobalamin intramuscularly daily for a week, then monthly for life is a reasonable option, but it is not as effective as the regimen described in choice A.

The initial daily dose is lower, and there is no weekly dosing phase to replenish stores quickly.

Choice D rationale:

Administering 2000 mcg of cyanocobalamin subcutaneously daily for a week, then monthly for life is not the preferred route for vitamin B12 supplementation in patients with pernicious anemia or severe malabsorption.

Intramuscular injection is the preferred route as it ensures better absorption, and subcutaneous injection may not be as effective.