Definition and Pathophysiologic Mechanisms

Hemolysis indicates premature destruction of red blood cells, reducing survival below normal 110-120 days.
Anemia develops when destruction rate exceeds compensatory bone marrow production capacity.
Normal marrow increases erythropoiesis six to eightfold under maximal stimulation during chronic hemolysis.
Destruction occurs via two primary pathophysiologic mechanisms: intravascular space destruction or extravascular reticuloendothelial system destruction.

Clinical Evaluation

Family history reveals anemia, jaundice, early-onset gallstones, splenectomy, or cholecystectomy.
Ethnic origin indicates specific risks: sickle trait in African ancestry, thalassemia trait in Mediterranean ancestry, glucose-6-phosphate dehydrogenase deficiency in Sephardic Jews.
Neonatal history reveals prominent early jaundice or phototherapy requirement.
Recurrent anemia episodes associate with reticulocytosis.
Anemia remains unresponsive to hematinics or iron supplementation.
Drug exposures, infections, or chemical exposures precipitate acute hemolytic events.
Dark urine passage correlates with dipyrroluria or hemoglobinuria.

General findings include pallor, fatigue, tachypnea, and tachycardia.
Jaundice provides prominent evidence of unconjugated hyperbilirubinemia.
Splenomegaly universally present in inherited membrane defects, thalassemias, and autoimmune hemolytic anemias.
Gallstones present secondary to chronic bilirubin excretion.
Skeletal changes manifest as frontal bossing, prominent facial bones, and maxillary hyperplasia due to massive marrow expansion.
Chronic leg ulcers occur notably in sickle cell disease.

Category	Intrinsic (Corpuscular) Defects	Extrinsic (Extracorpuscular) Defects
Inheritance	Primarily inherited (exceptions exist like paroxysmal nocturnal hemoglobinuria).	Primarily acquired.
Membrane defects	Hereditary spherocytosis, hereditary elliptocytosis, hereditary pyropoikilocytosis, hereditary stomatocytosis.	Paroxysmal nocturnal hemoglobinuria, spur cell anemia.
Enzyme defects	Glucose-6-phosphate dehydrogenase deficiency, pyruvate kinase deficiency.	None
Hemoglobin defects	Sickle cell syndromes, thalassemia syndromes, unstable hemoglobins.	None
Immune-mediated	None	Autoimmune hemolytic anemia (warm, cold), isoimmune (hemolytic disease of newborn, transfusion reaction), drug-induced.
Non-immune acquired	None	Microangiopathic hemolytic anemia, hypersplenism, infections (malaria, sepsis), toxins, thermal injury.

Pathologic red cell destruction produces distinct biochemical markers differentiating extravascular from intravascular compartments.

Biomarker	Extravascular Hemolysis	Intravascular Hemolysis
Unconjugated bilirubin	Elevated.	Elevated.
Serum lactate dehydrogenase	Elevated.	Markedly elevated.
Plasma haptoglobin	Decreased.	Markedly decreased or absent.
Plasma free hemoglobin	Normal.	Markedly elevated.
Urine findings	Increased urobilinogen.	Hemoglobinuria, hemosiderinuria.
Plasma methemalbumin	Normal.	Elevated.

Marrow response evaluation dictates functional capacity.
Reticulocyte count heavily elevated, frequently reaching 10-20%, occasionally up to 80%.
Reticulocyte Index response: Index = reticulocyte % x (observed hematocrit/normal hematocrit) x (1/maturation factor).
Increased mean corpuscular volume reflects large volume of young reticulocytes entering circulation.
Red cell distribution width widens substantially as hemoglobin falls and varying cell sizes emerge.
Peripheral smear displays nucleated red blood cells and polychromasia.
Bone marrow aspiration demonstrates striking erythroid hyperplasia with erythroid:myeloid ratio reversing to 1:1.

Functions as pivotal branch point distinguishing immune from non-immune etiologies.
Detects immunoglobulin g or complement (c3) fixed directly to red cell membrane.
Positive result establishes immune etiology including autoimmune hemolytic anemia, hemolytic transfusion reactions, or specific drug-induced mechanisms.
Reagent specificity differentiates warm autoimmune hemolytic anemia (predominantly immunoglobulin g) from cold agglutinin disease (predominantly complement c3).
Negative result directs evaluation toward intrinsic corpuscular defects, microangiopathic processes, or non-immune acquired causes.

Evaluation of cellular morphology provides immediate diagnostic direction regarding specific underlying structural or mechanical defects.

Morphological Finding	Diagnostic Association	Pathophysiologic Mechanism
Spherocytes	Hereditary spherocytosis, autoimmune hemolytic anemia.	Membrane surface area loss relative to volume; antibody-mediated membrane plucking.
Schistocytes, helmet cells, burr cells	Microangiopathic hemolytic anemia, hemolytic uremic syndrome, disseminated intravascular coagulation, mechanical valves.	Mechanical fragmentation from fibrin strands or abnormal vascular surfaces.
Bite cells, blister cells	Glucose-6-phosphate dehydrogenase deficiency, unstable hemoglobins.	Splenic pitting of precipitated denatured hemoglobin (Heinz bodies).
Sickle cells	Sickle cell disease.	Polymerization of deoxygenated hemoglobin s.
Target cells	Hemoglobinopathies (hemoglobin c, sickle cell), thalassemias, liver disease.	Increased membrane surface area to volume ratio.
Elliptocytes	Hereditary elliptocytosis.	Horizontal membrane skeleton linkage defects.
Basophilic stippling	Thalassemia, lead toxicity, pyrimidine 5-nucleotidase deficiency.	Ribosomal ribonucleic acid aggregates.
Acanthocytes	Liver disease, abetalipoproteinemia.	Altered cholesterol-to-phospholipid membrane ratio.
Teardrop cells	Thalassemia major, myelofibrosis.	Extramedullary hematopoiesis or marrow fibrosis.

Membrane defects: Eosin-5-maleimide binding test utilizes flow cytometry to detect band 3 reduction, offering high sensitivity for hereditary spherocytosis. Incubated osmotic fragility test demonstrates premature lysis in hypotonic solutions.
Enzyme deficiencies: Specific quantitative spectrophotometric enzyme assays confirm glucose-6-phosphate dehydrogenase or pyruvate kinase reductions. Testing must be deferred post-acute hemolysis in glucose-6-phosphate dehydrogenase deficiency due to falsely normal levels in young reticulocytes.
Hemoglobinopathies: High-performance liquid chromatography or cellulose acetate hemoglobin electrophoresis quantifies variant hemoglobins.
Paroxysmal nocturnal hemoglobinuria: Flow cytometric analysis definitively identifies absence of glycosylphosphatidylinositol-anchored surface proteins cd55 and cd59 on erythrocytes and granulocytes.
Unusual immune defects: Donath-Landsteiner test identifies paroxysmal cold hemoglobinuria via biphasic immunoglobulin g autoantibody that binds in cold and lyses upon warming.