Anemia — by MCV, comprehensively

◆Microcytic (MCV < 80)

• •Iron deficiency: ↓ ferritin (most specific), ↑ TIBC, ↓ transferrin saturation; pica; blood loss until proven otherwise
• •Anemia of chronic disease: ↑ ferritin (acute-phase), ↓ TIBC, normal-low serum iron; treat underlying inflammation
• •Thalassemia: target cells, basophilic stippling; trait → microcytic with NORMAL iron studies; α has 4 alleles, β has 2
• •Sideroblastic anemia: ringed sideroblasts on marrow; causes: lead, alcohol, isoniazid (give B6), copper deficiency, MDS
• •Lead poisoning: basophilic stippling, microcytic anemia, abdominal pain, neuropathy; check serum lead; chelate with succimer (peds) or EDTA

◆Normocytic (MCV 80–100)

• •Anemia of chronic kidney disease: ↓ EPO; treat with EPO replacement when Hb <10, iron stores adequate
• •Hemolysis: ↑ LDH, ↑ indirect bili, ↓ haptoglobin, ↑ reticulocytes
• •Hereditary spherocytosis: NORTHERN European, family history, ↑ MCHC, NEGATIVE Coombs, splenomegaly; splenectomy if severe
• •G6PD deficiency: oxidative stress (sulfa, antimalarials, fava beans, infections) → bite cells + Heinz bodies; check level after acute episode resolves
• •Warm AIHA: IgG, spherocytes, POSITIVE direct Coombs; SLE, CLL, drugs (methyldopa); steroids first-line
• •Cold AIHA: IgM, Mycoplasma, EBV; cold avoidance; rituximab refractory
• •MAHA: schistocytes; TTP/HUS/DIC/HELLP/malignant HTN/mechanical valves

◆Macrocytic (MCV > 100)

• •B12 deficiency: ↑ MMA + ↑ homocysteine; neuro symptoms (subacute combined degeneration); pernicious anemia (autoimmune anti-IF), strict vegan, ileal disease
• •Folate deficiency: ↑ homocysteine + NORMAL MMA; no neuro symptoms; alcoholics, methotrexate, pregnancy
• •Non-megaloblastic: alcohol, liver disease, hypothyroidism, MDS, drugs (hydroxyurea, zidovudine)
• •Reticulocytosis: any cause of hemolysis or recent bleeding can cause apparent macrocytosis

◆Special situations

• •Sickle cell disease: vaso-occlusive crisis, acute chest syndrome, splenic sequestration in kids, aplastic crisis (parvovirus B19)
• •Hydroxyurea reduces SCD crises; transfusions for severe; vaccinations critical (Pneumococcus, Hib, Meningococcus due to functional asplenia)
• •Paroxysmal nocturnal hemoglobinuria: morning dark urine + thrombosis + pancytopenia; CD55/CD59 deficiency; eculizumab
• •Aplastic anemia: pancytopenia + hypocellular marrow + NO hepatosplenomegaly; idiopathic, drugs (chloramphenicol, sulfa), viruses; stem cell transplant
• •Pure red cell aplasia: only RBC line affected; parvovirus B19 (esp in immunocompromised) or thymoma

Smear findings ↔ diagnosis