Management of Elevated MCV and MCH

Initial Diagnostic Workup

The combination of elevated MCV and MCH most strongly suggests vitamin B12 or folate deficiency, though myelodysplastic syndrome, hemolysis, or mixed deficiency states must also be considered 1
Vitamin B12 and folate levels are mandatory first-line tests to identify macrocytic deficiency 1
Serum ferritin and transferrin saturation must be checked to identify coexisting iron deficiency, which can mask the full expression of macrocytosis 1
Reticulocyte count distinguishes between deficiency states versus hemolysis or bleeding response 1
C-reactive protein (CRP) identifies inflammation that affects ferritin interpretation 1
Haptoglobin and LDH assess for hemolysis if reticulocytes are elevated 1

For B12 deficiency with neurological involvement, administer hydroxocobalamin 1 mg intramuscularly on alternate days until no further improvement, then continue hydroxocobalamin 1 mg intramuscularly every 2 months for life 2
For B12 deficiency without neurological involvement, administer hydroxocobalamin 1 mg intramuscularly three times weekly for 2 weeks, followed by maintenance treatment of 1 mg intramuscularly every 2-3 months for life 2
Critical: Always exclude vitamin B12 deficiency before treating folate deficiency, as folate supplementation may mask severe B12 depletion and allow irreversible neurological damage to progress 2, 1
For folate deficiency, oral folic acid 5 mg daily for a minimum of 4 months 2
For patients with MDS-related macrocytic anemia, lenalidomide for individuals with del(5q) cytogenetic abnormality, erythropoietin therapy for patients with normal cytogenetics, and consider G-CSF addition if no response occurs with erythropoietin alone 1

Serial monitoring of MCV, MCH, and reticulocyte count helps assess response to vitamin or iron replacement 1

Immediate hematology consultation is required if the cause remains unclear after complete workup, suspicion for myelodysplastic syndrome exists, hemolytic anemia is confirmed, pancytopenia is present, or no response to appropriate vitamin or iron replacement after 2-3 weeks 1

Certain medications cause macrocytosis with elevated red cell indices, including anticonvulsants, methotrexate, sulfasalazine, and other chemotherapeutic agents 2, 3
Chronic alcohol use can cause macrocytosis independent of nutritional deficiencies 3

Folate deficiency causes megaloblastic anemia with macrocytosis, though less commonly than B12 deficiency, particularly in patients with inflammatory bowel disease 4
Anticonvulsants such as diphenytoin can elevate MCV, according to the National Comprehensive Cancer Network 5
Renal insufficiency can contribute to normocytic or macrocytic anemia, as stated by the National Comprehensive Cancer Network 6
In patients with myelodysplastic syndrome, erythropoietin therapy (40,000-60,000 units subcutaneously 1-3 times weekly) may be considered for patients with normal cytogenetics, <15% marrow ringed sideroblasts, and serum erythropoietin ≤500 mU/mL, as recommended by the National Comprehensive Cancer Network 5

Increased homocysteine indicates tissue deficiency of either B12 or folate with greater sensitivity than serum B12 measurement, according to the Journal of Crohn's and Colitis 4
Methyl malonate is specific for B12 deficiency with better sensitivity, as stated by the Journal of Crohn's and Colitis 4
IBD patients require annual measurement of B12 and folate, or more frequently if macrocytosis present or if small bowel disease/resection exists, as recommended by the Journal of Crohn's and Colitis 4