Blood Disorders, Transfusion, Anemia, Hemolysis, Sickle Cell Disease, Polycythemia & Leukopenia

Blood Transfusion Fundamentals

• Purpose
  • Replaces lost/deficient red blood cells (RBCs) and other blood components.
• ABO & Rh systems
  • 4 ABO types determined by surface antigens A and B.
  • Rh determined by presence (Rh⁺) or absence (Rh⁻) of antigen D.
  • Example: “A⁺” = A‐antigen + D‐antigen.
  • Example: “O⁻” = no A, no B, no D antigens.
• Transfusable RBC products
  • Whole blood, packed RBCs, leukocyte-reduced RBCs, washed RBCs, frozen RBCs.
• Universal donor
  • O⁻ used for uncross-matched emergency/trauma transfusion.
• Best practice
  • Full type-and-screen + cross-match whenever time allows.
• Course focus
  • Detailed immunologic transfusion reactions exist but will not be tested; emphasis remains on systemic disease processes.

Anemia: Definition, Causes & Symptoms

• Definition
  • Abnormally low number of circulating RBCs or/and low hemoglobin → ↓ oxygen-carrying capacity.
• Oxygen deficit produces tissue hypoxia‐based clinical picture.
• Major etiologic groups
  1. Blood loss
  • Acute (trauma, massive GI bleed) → abrupt symptoms.
  • Chronic (menorrhagia, occult GI bleed, peptic ulcer) → insidious, compensatory adaptation.
  1. Hemolysis (premature destruction) – see dedicated section.
  2. Impaired production
  • Nutritional deficiency: iron, vitamin B₁₂, folic acid.
  • Bone-marrow failure/aplastic anemia.
  • Erythropoietin lack in end-stage renal disease.
  • Malnutrition or malabsorption (alcoholism, gastric surgery, anorexia, dysphagia, tube feeds).
• Cardinal symptoms/signs (hypoxia-driven)
  • Fatigue, malaise, pallor (sclerae, palmar creases, mucosa), weakness.
  • Dyspnea, dizziness.
  • Late: tachycardia, chest pain, possible elevated troponin / ischemic ECG changes.
• Important laboratory clue
  • Severely low hemoglobin (e.g., $Hgb=3\text{ g dL}^{-1}$) in minimally symptomatic, long-standing chronic loss.
• Key anemia subtypes for this course
  • Iron-deficiency.
  • Megaloblastic (vitamin B₁₂, folate).
  • Aplastic.
  • Anemia of chronic renal disease (↓ erythropoietin).

Hemolysis (RBC Destruction)

• Normal physiology
  • RBC life span ≈ $120\text{ days}$; senescent cells removed by RES.
• Pathologic when:
  • Destruction premature or rate exceeds marrow replacement.
• Extravascular hemolysis
  • Occurs outside vessels (spleen, liver).
  • Trigger: membrane deformation; organs phagocytose abnormal cells.
• Intravascular hemolysis
  • Lysis within bloodstream.
  • Causes: autoimmune antibodies, transfusion incompatibility, mechanical injury, toxins.

Sickle Cell Disease (SCD)

• Genetics & Molecular defect
  • Point mutation in β-globin chain: valine replaces glutamic acid → Hemoglobin S (HbS).
  • HbS gene recessive.
  • Trait: 1 HbS allele.
  • Disease: 2 HbS alleles (homozygous).
• Pathophysiology
  • Deoxygenation polymerizes HbS → distorted "sickle" shape.
  • Re-oxygenation may reverse early, but repetitive cycles → irreversible sickling.
  • Degree of sickling ∝ % HbS; patients with lower concentrations may be asymptomatic.
• Major clinical manifestations
  • Chronic hemolytic anemia & hyperbilirubinemia.
  • Vaso-occlusive crises → acute severe pain (abdomen, chest, bones, joints).
  • Bone infarcts → avascular necrosis (hips/shoulders common).
  • Organ infarcts: liver, spleen, heart, kidneys.
  • Acute Chest Syndrome – leading cause of death
  • Sudden chest pain, cough, pulmonary infiltrate, dyspnea, respiratory failure.
• Precipitating factors
  • Infection, cold exposure, dehydration, acidosis, excessive exertion.
• Management principles
  • Rapid oxygenation + aggressive IV hydration + multimodal analgesia until sickling resolves.
  • Preventive strategies: avoid triggers; prompt treatment of infections (e.g., COVID-19, influenza, URI, gastroenteritis).
  • Chronic therapy: hydroxyurea (↑ HbF), daily folic acid; transfusions guided by individualized baseline hemoglobin (e.g., transfuse at $Hgb\le6$ or $\le7\text{ g dL}^{-1}$ depending on baseline).
• Diagnostics
  • Screening hemoglobin solubility test → confirm by electrophoresis.
  • No definitive cure; bone-marrow transplant experimental for select cases.

Polycythemia (↑ RBC Mass)

• Definition
  • Hematocrit thresholds: men >54\%, women >47\%.
  • Blood viscosity rises; Hct>50\% → cardiac strain, Hct>60\% → tissue hypoxia.
• Relative Polycythemia
  • Loss of plasma volume with intact RBC mass (dehydration, excessive diuretics, GI fluid loss).
  • Corrected by IV fluid replacement; labs normalize.
• Absolute Polycythemia (↑ RBC production)
  1. Primary – Polycythemia Vera (PV)
  • Myeloproliferative neoplasm: ↑ RBC + ↑ WBC + ↑ platelets.
  • Hyper-viscosity manifestations: hypertension, headache, dizziness, concentration impairment, visual disturbance, central cyanosis.
  • Risk of thrombosis and paradoxical hemorrhage.
  • Treatment: serial phlebotomy to lower Hct; myelosuppressive drugs PRN.
  1. Secondary
  • Compensatory ↑ erythropoietin from chronic hypoxia (COPD, cyanotic heart/lung disease, high altitude, smoking).
  • Therapy: treat underlying disorder, low-flow O₂ to relieve hypoxia.
• Additional shared findings (especially in long-standing cases)
  • Splenomegaly, iron depletion, ↓ cardiac output, venous stasis, thrombo-embolism, hemorrhage.

White Blood Cell (Leukocyte) Development

• Origination in bone marrow stem cells
  • Myeloid stem cell → granulocytes (neutrophils, eosinophils, basophils) & monocytes.
  • Lymphoid stem cell → lymphocytes (T, B, NK).
• "Blasts" = immature precursors; high circulating blast count abnormal and suggest marrow pathology.

Leukopenia & Neutropenia

• Terminology
  • Leukopenia: ↓ total leukocyte count.
  • Neutropenia: ↓ absolute neutrophil count (ANC).
  • Agranulocytosis: near-absence of neutrophils.
  • Pancytopenia: ↓ RBC + WBC + platelets (myeloid stem cell failure).
• Infection risk
  • Directly proportional to depth and duration of neutropenia.
• Etiologies
  • Congenital.
  • Autoimmune.
  • Accelerated peripheral removal.
  • Drug-induced.
  • Cyclic.
  • Marrow neoplasms.
  • Idiopathic.
• Clinical presentation
  • Early: bacterial/fungal infection → malaise, chills, fever, profound fatigue, weakness.
  • Lab: low WBC / ANC on CBC.
• Autoimmune Neutropenia
  • Pathogenesis: antibodies against neutrophil membranes or progenitors; immune complex-mediated destruction.
  • Primary (children): rare, self-limited, mild–moderate infections; antibiotics suffice.
  • Secondary: associated with systemic diseases (Rheumatoid Arthritis, SLE).
  • Felty Syndrome = RA + splenomegaly + neutropenia + recurrent pulmonary infections.
  • Serious infections → sepsis; management focuses on prompt antimicrobial therapy & prevention.

High-Yield Numerical & Laboratory Benchmarks

• RBC life span ≈ $120\text{ days}$.
• Critical hemoglobin example: $Hgb=3\text{ g dL}^{-1}$ (severe, suggests chronic loss if minimal acute signs).
• Polycythemia thresholds
  • Men: Hct>54\%, Women: Hct>47\% (diagnostic); Hct>60\% = severe hyperviscosity/hypoxia risk.
• Baseline transfusion practice in SCD varies (e.g., transfuse when $Hgb\le6$ g/dL if baseline ≈7).

Clinical Connections & Practical Implications

• Chronic anemias may masquerade as "fatigue"; always inspect conjunctiva, palms, mucosa for pallor.
• In trauma/emergency, O⁻ blood saves lives when no cross-match time exists.
• Recurrent pain crises in SCD demand early hydration & oxygen to pre-empt organ damage.
• Aggressive fluid resuscitation not only treats dehydration but corrects "relative" polycythemia.
• Hypertensive, dizzy patient with elevated hematocrit? – Think polycythemia vera vs secondary hypoxia.
• Neutropenic patient with fever is an oncologic emergency; begin broad-spectrum antibiotics immediately.