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Anemia — Complete Study Guide (Questions 53–66)

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53. Modern Classification of Anemia

A. By Red Cell Size (MCV-Based) — Wintrobe Classification

B. By Mechanism (Reticulocyte-Based)

• Bleeding (hemorrhage)
• Hemolysis — acquired (autoimmune, mechanical) or congenital (enzyme defects, hemoglobinopathies, membrane defects)

• Nutritional deficiency: iron, B12, folate, copper, vitamin C
• Absence of red cell precursors: aplastic anemia, pure red cell aplasia
• Lack of erythropoietin: renal disease, anemia of inflammation, aging
• Marrow replacement: neoplasm, infection, granulomatous disease
• Stem cell defects: myelodysplasia, leukemia

Anemia is defined as blood counts below normal for a given population. — Harrison's Principles of Internal Medicine 22E, p. 492

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54. Etiological Factors Contributing to Anemic Syndrome

1. Decreased Red Cell Production

• Nutritional deficiency: Iron (most common worldwide), vitamin B12, folate
• Bone marrow suppression: Toxins, radiation, drugs (chemotherapy, chloramphenicol)
• Marrow replacement: Leukemia, lymphoma, metastatic carcinoma, myelofibrosis
• Reduced erythropoietin: Chronic kidney disease, endocrine disorders (hypothyroidism, Addison's disease)
• Chronic inflammation: Cytokine-mediated inhibition of iron reutilization and erythropoietin response

2. Increased Red Cell Destruction (Hemolysis)

• Intrinsic (congenital) RBC defects: membrane, enzyme, or hemoglobin abnormalities
• Extrinsic (acquired): autoimmune antibodies, infections, toxins, mechanical trauma, hypersplenism

3. Blood Loss

• Acute: Trauma, surgery, GI hemorrhage
• Chronic: GI bleeding (peptic ulcer, cancer, hookworm), menorrhagia, frequent phlebotomy

At least 75% of all cases of anemia are hypoproliferative in nature; the most common cause is mild to moderate iron deficiency or inflammation. — Harrison's 22E, p. 492

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55. Classification of Hemolytic Anemias: Congenital and Acquired Forms

Classification by Site

• Intravascular hemolysis: Free hemoglobin released into bloodstream → hemoglobinemia, hemoglobinuria, acute renal failure risk (e.g., ABO incompatibility, G6PD in oxidative crisis)
• Extravascular hemolysis: RBCs removed by macrophages in spleen/liver → jaundice, splenomegaly (e.g., hereditary spherocytosis, warm AIHA)

Classification by Origin

There are multiple classification systems for hemolytic anemias based on Coombs test reactivity, intrinsic vs. extrinsic defects, intravascular vs. extravascular hemolysis, and congenital or acquired forms. — Rosen's Emergency Medicine, p. 2446

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56. Diagnostic Criteria for Iron Deficiency Anemia (IDA)

Clinical Features

• Fatigue, pallor, dyspnea on exertion (from anemia)
• Koilonychia (spoon nails), alopecia, atrophic glossitis, pica (craving for clay, ice)
• Esophageal webs (Plummer-Vinson syndrome in severe, chronic cases)

Laboratory Findings

Peripheral Blood Smear

• Microcytes, hypochromic cells with enlarged central pallor
• "Pencil cells" (elongated poikilocytes)

Bone Marrow

• Absent stainable iron (Prussian blue stain — most definitive finding)
• Mild to moderate erythroid hyperplasia

Response to Treatment

• Reticulocytosis within 5–7 days of oral iron
• Steady rise in Hb over 4–8 weeks

The diagnosis of iron deficiency anemia ultimately rests on laboratory studies: low serum iron, low ferritin, elevated TIBC, transferrin saturation below 15%. — Robbins & Kumar Pathology, p. 615

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57. Diagnostic Criteria for B12 and Folate Deficiency Anemia

Clinical Features

Laboratory Findings

Differentiating B12 from Folate Deficiency

• Elevated methylmalonic acid → B12 deficiency (not folate)
• Normal methylmalonic acid + low folate → folate deficiency
• Neurologic findings → B12 deficiency only
• Body stores: B12 stores last 3–5 years; folate stores last only 2–4 months

The hematologic findings are identical in B12 and folate deficiency. Methylmalonic acid is elevated in B12 but not folate deficiency. Neurologic changes do not occur with folate deficiency alone. — Robbins & Kumar, p. 612

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58. Diagnostic Criteria for Hypo- and Aplastic Anemia

Clinical Features

• Symptoms of anemia: fatigue, pallor, dyspnea
• Thrombocytopenia: petechiae, purpura, mucosal bleeding
• Neutropenia: recurrent infections

Diagnostic Criteria (Severe Aplastic Anemia — International AA Study Group)

• Neutrophils < 0.5 × 10⁹/L
• Platelets < 20 × 10⁹/L
• Reticulocytes < 20 × 10⁹/L (< 1%)

• Cellularity < 25% (or < 50% with < 30% residual hematopoietic cells)
• Replacement of marrow space by fat cells

Laboratory Features

• Pancytopenia (all cell lines reduced)
• Normocytic or mildly macrocytic anemia
• Low/absent reticulocytes
• Normal RBC morphology (no dysplasia)
• Normal or elevated MCV
• Elevated erythropoietin

Bone Marrow (critical)

• Hypocellular or acellular marrow biopsy
• Fat cell replacement
• No dysplasia, no blasts, no fibrosis
• Prussian blue: absent iron in aplasia vs present in MDS

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59. Diagnostic Criteria for Hemolytic Anemia

General Diagnostic Criteria

• Reticulocytosis (elevated reticulocyte count)
• Bone marrow erythroid hyperplasia (↑ M:E ratio inversion)

• Spherocytes → hereditary spherocytosis, warm AIHA
• Schistocytes (helmet cells) → MAHA (TTP, DIC, prosthetic valves)
• Sickle cells → sickle cell disease
• Target cells → HbC, thalassemia, liver disease

• Direct Coombs (DAT): Positive in immune-mediated HA → confirms autoantibody/complement on RBC surface
• Indirect Coombs: Characterizes antibody type/target
• Osmotic fragility test: Hereditary spherocytosis
• Hb electrophoresis: Hemoglobinopathies
• G6PD enzyme assay: G6PD deficiency
• Flow cytometry (CD55/CD59 deficiency): PNH

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60. Differential Diagnosis: Hypo-Aplastic Anemia vs. Leukemia

Key distinguishing feature: bone marrow biopsy. Aplastic anemia shows a hypocellular marrow with fat replacement and no blasts; leukemia shows a hypercellular marrow packed with malignant blast cells. — Rosen's Emergency Medicine

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61. Laboratory Indicators for Hypo- and Aplastic Anemia

CBC and Peripheral Blood

• Anemia: Normocytic (MCV normal or slightly elevated), normochromic
• Leukopenia: Particularly neutropenia (< 1.5 × 10⁹/L in mild; < 0.5 × 10⁹/L in severe)
• Thrombocytopenia: Platelet count < 50–20 × 10⁹/L
• Reticulocyte count: Very low (< 20 × 10⁹/L) — critical finding
• No blasts, no dysplastic changes on smear

Other Tests

• Erythropoietin: Elevated (compensatory)
• Iron studies: Normal or elevated serum iron; normal to elevated ferritin (no utilization)
• Serum B12/folate: Normal
• Liver function tests: Hepatitis serology (post-hepatitis aplastic anemia)
• Flow cytometry (PNH clone): CD55/CD59 negative population
• Chromosomal analysis (peripheral blood): For Fanconi anemia (chromosomal breakage)

Bone Marrow Aspirate and Biopsy

• Aspirate: "Dry tap" or very hypocellular sample; fatty stroma
• Biopsy (trephine): Definitive — hypocellular marrow (< 25–30% cellularity), fat replacement, residual lymphocytes and plasma cells, absence of hematopoietic precursors
• No dysplasia, no fibrosis, no blasts

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62. Methods of Bone Marrow Examination

1. Bone Marrow Aspiration (BMA)

• Site: Posterior iliac crest (preferred), sternum (sternal aspiration — emergency use), anterior iliac crest, tibial bone (in infants)
• Procedure: Needle aspiration of marrow fluid; smears prepared and stained (Giemsa/Wright, Perls' Prussian blue for iron, PAS, Sudan black)
• Yields: Cytology of individual cells — morphology of erythroid, myeloid, megakaryocytic series; M:E ratio; blast percentage; iron stores
• Limitations: May be a "dry tap" in fibrosis or aplasia; does not assess overall architecture

2. Bone Marrow Biopsy (Trephine Biopsy)

• Site: Posterior superior iliac spine
• Procedure: Core biopsy taken with a Jamshidi or Westerman-Jensen needle; formalin-fixed, paraffin-embedded; sections stained with H&E, reticulin, iron
• Yields: Marrow cellularity, architecture, presence/extent of fibrosis, infiltration (tumor, granulomas), megakaryocyte distribution
• Essential for: Aplastic anemia, myelofibrosis, lymphoma staging, hypocellular states, "dry tap"

3. Special Stains on Marrow Preparations

4. Ancillary Studies

• Flow cytometry: Immunophenotyping (leukemias, PNH clones)
• Cytogenetics/FISH: Chromosomal abnormalities (leukemia, MDS)
• Molecular studies: JAK2, BCR-ABL, FLT3, NPM1, etc.
• Culture: For infection (tuberculosis, fungal)

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63. Diagnosis and Principles of Treatment of Iron Deficiency Anemia

Diagnosis (Summary)

• History: chronic blood loss (GI, menorrhagia), dietary insufficiency, malabsorption, pregnancy
• CBC: microcytic hypochromic anemia
• Iron studies: ↓ serum iron, ↓ ferritin, ↑ TIBC, transferrin saturation < 15%
• Peripheral smear: microcytes, hypochromia, pencil cells
• In adult males/postmenopausal females: must exclude GI malignancy as source

Principles of Treatment

• Treat GI bleeding source, fibroids, malabsorption, dietary deficiency

• Ferrous sulfate 325 mg TID (65 mg elemental iron/dose) — standard
• Take on empty stomach for best absorption; vitamin C enhances absorption
• Expected response: reticulocytosis in 5–7 days; Hb rises ~1–2 g/dL per 2–3 weeks
• Treat for 3–6 months after Hb normalization to replenish stores
• Side effects: nausea, constipation, dark stools

• Malabsorption (celiac disease, gastric bypass)
• Intolerance to oral iron
• Need for rapid repletion (severe anemia, chronic dialysis)
• Agents: iron sucrose, ferric gluconate, ferric carboxymaltose, low-molecular-weight iron dextran

• Reserved for severe symptomatic anemia (Hb < 7 g/dL) or hemodynamic instability

• Increase dietary heme iron (red meat, poultry, fish)
• Avoid tea/coffee with meals (inhibit absorption)

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64. Iron-Containing Drugs: Indications and Contraindications

Oral Iron Preparations

• Hemochromatosis / hemosiderosis (iron overload)
• Hemolytic anemia without iron deficiency (can worsen iron overload)
• Active inflammatory bowel disease (may worsen GI irritation)
• Repeated transfusions (risk of secondary iron overload)
• Thalassemia (unless IDA confirmed)

• Reduces absorption of: fluoroquinolones, tetracyclines, levothyroxine, levodopa, bisphosphonates (separate by 2–4 hours)
• Absorption decreased by: antacids, calcium, coffee, tea, PPI therapy

Parenteral Iron Preparations

• Oral intolerance/non-compliance
• Malabsorption syndromes
• Active/ongoing blood loss exceeding oral replenishment
• Chronic kidney disease (on dialysis or with EPO therapy)
• Inflammatory bowel disease
• Perioperative anemia optimization
• Heart failure with iron deficiency (even without anemia)

• Iron overload states
• Acute infection (iron may promote bacterial growth)
• Known hypersensitivity to preparation
• First trimester of pregnancy (for most preparations)

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65. Diagnosis and Principles of Treatment of B12 and Folate Deficiency Anemia

Diagnosis

• Macrocytic anemia (MCV > 100 fL)
• Peripheral smear: macro-ovalocytes, hypersegmented neutrophils (≥ 5 lobes)
• Low serum B12 (< 200 pg/mL) or low serum/RBC folate
• Elevated homocysteine (both); elevated methylmalonic acid (B12 only)
• Bone marrow: megaloblastic changes, hypercellularity
• Pernicious anemia (main cause of B12 deficiency): anti-intrinsic factor antibodies (specific), anti-parietal cell antibodies (sensitive); Schilling test (historical)
• Rule out B12 deficiency before starting folate — folate therapy corrects hematologic findings but does NOT prevent and may worsen neurologic deterioration from B12 deficiency

Treatment: B12 Deficiency

• Cause of B12 deficiency determines route:
  • Dietary deficiency: oral B12 1,000 µg/day (high-dose oral can compensate for lack of intrinsic factor via passive diffusion)
  • Pernicious anemia / malabsorption: IM/SC cyanocobalamin or hydroxocobalamin 1,000 µg daily × 7 days → weekly × 4 weeks → monthly (lifelong)
• Neurologic improvement may occur up to 6–12 months with treatment; subacute combined degeneration may be irreversible if longstanding
• Reticulocytosis peaks at 5–7 days; Hb normalizes over 1–2 months

Treatment: Folate Deficiency

• Oral folic acid 1–5 mg/day for 4 months (until stores replenished)
• Treat underlying cause: alcohol cessation, manage malabsorption
• Pregnancy prophylaxis: 0.4–0.8 mg/day (reduces neural tube defects)
• Folinic acid (leucovorin) for drug-induced folate deficiency (methotrexate, trimethoprim)

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66. Diagnosis and Principles of Treatment of Hemolytic Anemia

Diagnosis

• ↑ LDH, ↓ haptoglobin, ↑ indirect bilirubin, ↑ reticulocytes
• Hemoglobinuria/hemosiderinuria (intravascular)

• Direct Coombs test (DAT): If positive → immune-mediated (AIHA, drug-induced)
• Peripheral smear: Spherocytes (AIHA, hereditary spherocytosis), schistocytes (MAHA), sickle cells, target cells
• Osmotic fragility: Hereditary spherocytosis
• Hb electrophoresis: Sickle cell, thalassemia, HbC
• G6PD assay: G6PD deficiency (sample after acute episode when reticulocytes normalized)
• Flow cytometry (CD55/CD59): PNH
• Bone marrow: Erythroid hyperplasia; for PNH/aplastic context

Principles of Treatment

1. Corticosteroids (first-line): Prednisolone 1 mg/kg/day → taper over months
2. Splenectomy: Second-line if steroid failure/dependence
3. Rituximab (anti-CD20): Effective for refractory cases
4. Immunosuppressants: Azathioprine, cyclophosphamide (third-line)
5. Blood transfusion: Only for life-threatening anemia (cross-matching is difficult)
6. Treat underlying cause: Lymphoma, SLE, drugs

• Avoidance of cold
• Rituximab (most effective)
• Plasmapheresis (acute severe)
• Steroids less effective

• Avoid oxidant triggers (drugs — see Box above, fava beans, infections)
• Supportive: hydration, transfusion in acute crises
• No enzyme replacement available

• Splenectomy (curative for hemolysis — removes main destruction site)
• Folic acid supplementation (chronic hemolysis increases folate demand)
• Cholecystectomy if gallstones

• Hydroxyurea (increases HbF production)
• Prophylactic penicillin + pneumococcal vaccination
• Chronic transfusion (stroke prevention)
• Hematopoietic stem cell transplantation (potentially curative)
• Voxelotor, crizanlizumab (newer agents)

• Eculizumab/ravulizumab (anti-C5 complement inhibitors) — reduces hemolysis and thrombosis
• Hematopoietic stem cell transplantation (only cure)
• Anticoagulation (thrombosis prevention)
• Meningococcal vaccination required before C5 inhibitor therapy

• Immunosuppression with anti-thymocyte globulin (ATG) + cyclosporine
• Eltrombopag (TPO receptor agonist)
• HSCT for severe cases in young patients

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