Diagnostic Approach to Macrocytic Anemia

Initial Evaluation

The presentation of low hemoglobin, low RBC count, and high MCH indicates macrocytic anemia, most commonly caused by vitamin B12 or folate deficiency, and requires immediate measurement of serum B12 and folate levels followed by appropriate supplementation, as recommended by the Kidney International guidelines 1
Complete blood count with red cell indices should be performed to confirm MCV is elevated, and absolute reticulocyte count should be assessed to evaluate bone marrow response, according to the Kidney International guidelines 1
Peripheral blood smear should be evaluated for hypersegmented neutrophils (B12/folate deficiency) or other morphologic abnormalities, as suggested by the Kidney International guidelines 1

If folate deficiency is confirmed, folic acid 5 mg daily for 2 weeks, then 5 mg weekly for 6 weeks should be administered, with the critical caveat that folate should never be treated alone without excluding B12 deficiency first, as folate can mask B12 deficiency while allowing irreversible neurologic damage to progress, according to the Kidney International guidelines 1
If both deficiencies are present, both should be treated simultaneously with appropriate supplementation of each, as recommended by the Kidney International guidelines 1

Repeat CBC after 4-8 weeks to confirm hemoglobin rise, with an expected response of hemoglobin increase of 1-2 g/dL every 2-4 weeks with appropriate treatment, according to the Praxis Medical Insights guidelines 3 and 4
Reticulocyte count should increase within 1 week of starting therapy, indicating bone marrow response, as suggested by the Kidney International guidelines 1

Do not assume iron deficiency, as high MCH excludes typical iron deficiency anemia, according to the Praxis Medical Insights guidelines 2
Do not treat empirically without confirming the specific deficiency, as B12 and folate deficiencies require different investigations for underlying causes, as recommended by the Kidney International guidelines 1
Do not overlook combined deficiencies, as iron deficiency can coexist with B12/folate deficiency, masking the macrocytosis and presenting with normal MCV but still elevated MCH, according to the Praxis Medical Insights guidelines 2