Macrocytosis, Hemolytic Anemia, and Myelodysplastic Syndrome: Clinical Diagnosis and Management

Step up your anemia game as we explore the causes and diagnostic approach for macrocytic anemia, what to do with a reticulocyte count, the differential diagnosis for hemolytic anemia, the significance of the direct antiglobulin test, and diagnosis and management pearls for autoimmune hemolytic anemia (AIHA) and myelodysplastic syndrome (MDS).

Understanding Macrocytosis

Macrocytosis occurs by two major mechanisms. One involves lots of young, normal cells due to reticulocytosis (“big, juicy, young cells”), while the other involves abnormal cells caused by abnormalities in lipid metabolism or red cell membranes or DNA synthesis with impaired cell division.

The differential diagnosis (DDx) for macrocytosis includes:

• Reticulocytosis
• Medications (especially antivirals, antimetabolites, and antineoplastic agents like methotrexate, HIV drugs, or chemotherapy)
• B12/folate deficiency
• Liver disease
• Chronic alcohol use (even a few drinks per day)
• Myelodysplastic syndrome (MDS)
• VEXAS (acquired bone marrow mutations lead to DNA damage and macrocytosis)

Regarding common primary care medications, allopurinol and metformin are drugs that you might forget cause macrocytosis. To assist in categorization, the following table summarizes the primary mechanisms and associated causes:

Diagnostic Approach and Hemolytic Anemia

A basic workup for macrocytosis involves a CBC with reticulocyte count and a comprehensive metabolic panel (CMP), which includes liver tests. Specifically, if there is high suspicion for B12 deficiency, you should send B12 and methylmalonic acid together to prevent a delay in diagnosis.

For patients where hemolytic anemia is suspected, note that elevated bilirubin is not sensitive, so check LDH, haptoglobin, and a reticulocyte count. The DDx for hemolytic anemia is broad and includes:

• Immune mediated (autoimmune disease, hemoglobinurias, transfusion reactions)
• Trauma (e.g., marching, cardiac valves)
• Microangiopathic (e.g., MAHA, DIC)
• Hemoglobinopathies (e.g., sickle cell), G6PD, and hereditary spherocytosis
• Infections (e.g., malaria) and lymphomas (esp. CLL)

A positive direct antiglobulin test (DAT) confirms a diagnosis of autoimmune hemolytic anemia.

Myelodysplastic Syndrome (MDS) Management

Clinical pearls for Myelodysplastic Syndrome suggest that one should refer to Hematology for suspected MDS when patients have numerous immature cells on a CBC with differential, progressive cytopenias (trajectory) and/or younger age. Factors to consider in the management of myelodysplastic syndrome include shared decision-making and determining when to perform a bone marrow biopsy.

Management approach for autoimmune hemolytic anemia often involves considerations for outpatient treatment, assessing clotting risk, and long-term prognosis regarding the recurrence of the condition.