Diagnostic Approach for Anemia with Elevated Mean Corpuscular Hemoglobin

Initial Laboratory Assessment

A complete blood count (CBC) with red cell indices is essential to confirm anemia and characterize the elevated MCH, which typically corresponds with macrocytosis (elevated MCV), according to the European Hematology Association 2, 3
Reticulocyte count should be obtained to assess bone marrow response - a low or normal count suggests impaired erythropoiesis while an elevated count suggests hemolysis or blood loss, as recommended by the American Society of Hematology 3, 1
Serum ferritin, transferrin saturation, and iron studies to rule out concomitant iron deficiency, as mixed deficiencies can occur, as noted by the National Institute of Diabetes and Digestive and Kidney Diseases 2, 4
C-reactive protein (CRP) to assess for underlying inflammation that may affect interpretation of iron studies, according to the European League Against Rheumatism 3, 4

Vitamin B12 and folate levels - deficiencies are the most common causes of macrocytic anemia with elevated MCH, as stated by the American College of Physicians 1
Lactate dehydrogenase (LDH), haptoglobin, and bilirubin if hemolysis is suspected, as recommended by the International Society of Hematology 3, 1

Methylmalonic acid and homocysteine levels if B12 deficiency is suspected despite normal B12 levels, as suggested by the Endocrine Society 1
Bone marrow examination may be necessary in cases where the diagnosis remains unclear after initial testing, particularly to rule out myelodysplastic syndromes or other primary bone marrow disorders, according to the American Society of Clinical Oncology 3
Consider hemoglobin electrophoresis to rule out hemoglobinopathies, especially in patients with appropriate ethnic background, as recommended by the National Heart, Lung, and Blood Institute 2

If elevated MCH is accompanied by elevated MCV (>100 fL), focus on causes of macrocytic anemia: check B12 and folate levels first, as recommended by the American College of Physicians 1
If elevated MCH occurs with normal MCV (80-100 fL): consider mixed deficiency states (e.g., combined iron and B12/folate deficiency), as noted by the European Hematology Association 2, 3
If elevated MCH occurs with hemolysis: check LDH, haptoglobin, and bilirubin, as recommended by the American Society of Hematology 1

An elevated MCH without macrocytosis may occur in hemoglobinopathies or in cases of laboratory error - confirm with repeat testing, as suggested by the International Society of Hematology 2
Patients on certain medications (especially thiopurines like azathioprine) may have macrocytosis without true vitamin deficiency, as noted by the European League Against Rheumatism 3, 4
Mixed nutritional deficiencies can mask typical findings - for example, concurrent iron deficiency can normalize MCV in a patient with B12 deficiency while MCH remains elevated, according to the National Institute of Diabetes and Digestive and Kidney Diseases 3
Reticulocytosis can cause elevated MCH without underlying vitamin deficiency - this represents a normal response to bleeding or hemolysis, as stated by the American College of Physicians 1