What follow-up tests are recommended for a patient with macrocytosis after initial treatment for vitamin B12 deficiency?

Follow-up tests for a patient with macrocytosis after initial treatment for vitamin B12 deficiency should not include repeating the initial diagnostic vitamin B12 tests if the patient is receiving intramuscular vitamin B12 replacement.

If symptoms persist, worsen, or new symptoms appear, consider increasing the frequency of vitamin B12 injections and investigate alternative diagnoses.

Further biochemical tests such as serum methylmalonic acid (MMA) or plasma homocysteine may be used if there is uncertainty about ongoing deficiency or treatment adequacy, especially if oral treatment is used or symptoms persist.

Agree a date for reassessment of symptoms and clinical status, and continue treatment if symptoms improve but the cause of deficiency is not addressed or unknown.