Macrocytic

Macrocytic Anemias

Characteristics: Large RBCs (MCV > 100 fL)
Causes:
- Megaloblastic Anemias:
  - Impaired DNA synthesis due to vitamin B12 or folate deficiency
  - Peripheral blood smear: Oval macrocytes, hypersegmented neutrophils (more than 5 lobes)
  - Lab findings:
    - Low vitamin B12 or folate levels
    - Elevated methylmalonic acid (MMA) and homocysteine levels (in B12 deficiency)
    - Elevated homocysteine levels (in folate deficiency)
  - Causes of B12 deficiency:
    - Pernicious anemia (autoimmune destruction of parietal cells in the stomach, leading to decreased intrinsic factor)
    - Malabsorption (e.g., Crohn’s disease, celiac disease)
    - Dietary deficiency (rare)
  - Causes of Folate Deficiency:
    - Inadequate intake (e.g., poor diet, alcoholism)
    - Malabsorption
    - Increased demand (e.g., pregnancy, hemolytic anemia)
    - Medications (e.g., methotrexate)
- Non-Megaloblastic Anemias:
  - Macrocytosis without hypersegmented neutrophils
  - Causes:
    - Alcoholism
    - Liver disease
    - Hypothyroidism
    - Myelodysplastic syndromes (MDS)
    - Reticulocytosis (increased number of reticulocytes due to hemolysis or blood loss)
    - Medications (e.g., hydroxyurea)

Complete Blood Count (CBC):
- Hemoglobin (HGB)
- Hematocrit (HCT)
- Red Blood Cell Count (RBC)
- Mean Corpuscular Volume (MCV)
- Mean Corpuscular Hemoglobin (MCH)
- Mean Corpuscular Hemoglobin Concentration (MCHC)
- Red Cell Distribution Width (RDW)
- White Blood Cell Count (WBC) and Differential
- Platelet Count
Peripheral Blood Smear:
- RBC morphology (size, shape, color)
- WBC differential
- Platelet estimate
Reticulocyte Count:
- Percentage and absolute number of reticulocytes
- Corrected Reticulocyte Count/Reticulocyte Production Index (RPI)
Iron Studies:
- Serum Iron
- Total Iron-Binding Capacity (TIBC)
- Transferrin Saturation
- Ferritin
Vitamin B12 and Folate Levels:
- Serum B12
- Red Blood Cell Folate
Methylmalonic Acid (MMA) and Homocysteine Levels:
- Elevated in B12 Deficiency
- Homocysteine also Elevated in Folate Deficiency
Hemoglobin Electrophoresis:
- Identifies abnormal hemoglobin variants (e.g., HbS, HbC)
Direct Antiglobulin Test (DAT):
- Detects antibodies or complement proteins on the surface of RBCs
Bone Marrow Examination:
- Cellularity
- Maturation of cell lines
- Presence of abnormal cells
Other Tests:
- Haptoglobin and LDH (for hemolysis)
- Coombs test (for autoimmune hemolytic anemia)
- Osmotic Fragility Test (for hereditary spherocytosis)
- G6PD Assay (for G6PD deficiency)

Anemia: Deficiency of red blood cells or hemoglobin
Macrocytic: Large red blood cells (MCV > 100 fL)
Reticulocyte: Immature red blood cell
Hemolysis: Destruction of red blood cells
Extramedullary Hematopoiesis: Blood cell production outside the bone marrow
Megaloblastic: Abnormal maturation of blood cells due to impaired DNA synthesis