Non

Non-Immune Hemolysis

Hemolysis: accelerated destruction of RBCs

Extravascular Hemolyis: accelerated RBC destruction by macrophages, mainly in spleen (also liver and bone marrow)

Intravascular Hemolysis: RBC destruction by lysis in the bloodstream

Intrinsic Hemolytic Processes: abnormal RBCs are damaged by normal processes in the patient

Extrinsic Hemolytic Processes: normal RBCs are damaged by disease processes in the patient

Ineffective Erythropoiesis: destruction of RBC precursors in the bone marrow or immediately upon leaving the marrow

Spurious Hemolysis: accidental destruction of RBCs in blood samples (i.e. , rapid draw through small bore needle)

Compensated Hemolysis: RBC production is equal to RBC loss

Aplastic Crisis: RBC production is suppressed

common causes: vitamin deficiency, infection (most common is parvovirus B19), toxins, drugs

Hemolytic Crisis: RBC destruction is increased (i.e. by toxins, infection, drugs)

Extravascular Hemolysis

Normal Splenic Function: traveling through the spleen produces stress in RBC via two mechanisms

cells must squeeze through small spaces as they travel from the splenic cords into the sinuses

difficulty of this passage leads to slow flow which causes metabolic stress (ß pH, ß O₂, ß glucose, Ý lactate)

Þ only the strong survive

reticular endothelial (RE) cells and macrophages ‘cull’ the RBCs that aren’t up to snuff: cells that were abnormal to begin with; cells that are at the end of their lifespan; cells with abnormalities that make them more susceptible to stress (ß ATP synthesis; membrane abnormalities, etc)

‘Pitting’: RE cells can also ‘condition’ RBCs with minor defects by biting out a part (i.e. Howell-Jolly bodies)

reticuloendothelial cells in the liver and bone marrow can also perform these duties

Processing of RBC components: after being phagocytosed, RBCs are broken down and processed separately

globin and other proteins: degraded to amino acids

Fe: bound to ferritin for transport, storage, reuse

heme: converted to bilirubin, glucuronated in the liver and excreted

Diseases Producing Extravascular Hemolysis

(1) RBC Membrane Diseases

Mechanisms:

mechanical abnormalities impede splenic transport

altered permeability Þ metabolic depletion

hereditary types (spherocytosis, elliptocytosis, stomatocytosis) are usually autosomal dominant and mutations most often involve spectrin or ankyrin (cytoskeletal components)

Clinical: mostly assymptomatic with infrequent hemolytic or aplastic crises; splenomegaly and gall-stones common

Treament: folate, splenectomy if it is severe

Special Tests: osmotic fragility test - incubate cells in sequentially more dilute saline, hemolysis occurs early

Direct Coombs’s test - to rule out immune mechanism

(2) Pyruvate Kinase Deficiency: decreased ATP production leads to splenic destruction of RBCs

rare, inherited disorder; smear will show burr cells
test for pyruvate kinase levels; treat with folate, transfusion, or splenectomy

(3) Nucleotide Enzyme Disorders: rare disorders; end result is inhibition of ATP production

adenosine deaminase; pyrimidine-5’ nucleotidase deficiency (results in basophilic stippling, like lead poisoning)

(4) Severe Hypophosphatemia: leads to low ATP levels Þ splenic destruction

rare complication of starvation, alcohol intox; manifests as spherocytes; test with phosphate level

(5) Spur Cell Anemias (acanthocytosis)

Mechanism: abnormal/increased lipid content impairs RBC pliability/permeability

target cells arise from increased membrane to volume ratio; splenic conditioning leads to spur cells

(a) Liver disease: abnormal lipoproteins Þ unesterified cholesterol in membranes; ominous complication of end stage liver disease; check LFTs

(b) Abetalipoproteinemia: absence of beta-lipoprotein leads to sphingomyelin uptake into RBC membrane - rare

(6) Other Extravascular Hemolytic diseases covered by later lectures

sickle cell; thalassemia; unstable hemoglobinsease; immune hemolytic anemias (IV or EV)

Intravascular Hemolysis – Processing of RBC Components

hemoglobin is released into the bloodstream where it dissociates into dimers and binds to haptoglobulin; these complexes are transported to the liver to be broken down into bilirubin, Fe, and amino acids

haptoglobulin is rapidly depleted, so excess free dimers accumulate rapidly

free hemoglobin dimers can be excreted in the urine, dissociate in the plasma, or be phagocytosed directly
they can also oxidize to methemoglobin (turns the plasma red; appears within 5 hours, cleared in 6-12)
methemoglobin binds hemopexin and is transported to the liver
when hemopexin is depleted, methemoglobin binds albumin (turns the plasma brown)

Response to Hemolysis

marrow can increase production 5x within one week; evidence for increased production: retics, polychromasia, fine basophilic stippling, nucleated RBCs

Howell-Jolly bodies and Pappenheimer bodies appear if the normal pitting function of the spleen is compromised
extramedullary hematopoiesis can further increase production up to 8x

Diseases Producing Intravascular Hemolysis

(1) Glucose-6-phosphate Dehydrogenase Deficiency: G-6-PD is involved in the regeneration of NADPH which is used to reduce glutathione; loss of G-6-PD results in greater senstivity to oxidative stress

X-linked recessive trait; affects 1 million worldwide

the most common mutation is a variant in the enzyme which renders it unstable Þ young RBCs are okay, but older RBCs become depleted as the enzyme wears out Þ complicates the diagnosis

Intravascular manifestations: oxidative stress (fava beans, primiquine, TMP-SMX) leads to hemolysis; bite cells

Extravascular manifestations: oxidation leads to precipitation of hemoglobin as Heinz bodies Þ splenic destruction

(2) Paroxysmal Nocturnal Hemoglobinuria

Mechanism: clonal proliferation of RBC and WBC with increased sensitivity to complement

Clinical: hemolysis Þ urinary Fe loss; thrombosis; treat with Fe, transfusion

Labs: Ham test for RBC complement sensitivity

(3) Infections

Clostridium: membrane damage from anti-phospholipid toxin; fulminant presentation with severe hemolyisis
Malaria, Babesiosis, Bartenellosis: parasites grow in RBCs (seen as RBC inclusions)

(4) Traumatic Hemolyis: due to high velocity, turbulent or constricted flow (HTN, aortic stenosis, prosthetic valve, etc)

usually mild hemolysis defined by shistocytes

(5) DIC (Disseminated Intravascular Coagulation): occurs with infection, pancreatitis, aortic dissection, malignancy, etc

endothelial damage Þ fibrin-rich microthrombi, bleeding and clotting, schistocytes, prolonged clotting times

(6) TTP (Thrombotic Thrombocytopenic Purpura)

classic symptoms (FAT RN): Fever, microangiopathic hemolytic Anemia, Thrombocytopenia, Renal and Neuro deficits

normal clotting times; platelet-rich microthrombi; 40% of patients have all five classic symptoms

90% mortality without treatment; 80% cure with treatment

DO NOT TRANSFUSE Þ can lead to stroke

Some Common Morphological Findings in Blood Smears

Cell Structure Abnormalities

Greek Term	Other Terms	Clinical Association	Appearance
Discocyte	Normocyte	Normal	Normal round RBC
Elliptocyte	Elliptocyte, ovalocyte	Hereditary ellitocytosis	Elongated with parallel sides or egg-shaped common in camels
Spherocyte	Spherocyte	Immune mediated hemolysis hereditary spherocytosis	Round with little or no central pallor
Stomatocyte	Stomatocyte	hereditary stomatocytosis	Slit-like central pale area
Codocyte	Target cell	non-specific (Thalassemias, homozygous hemoglobin C disease	Hemoglobin color in center and periphery; bullseye
Schistocyte	Fragment	TTP; DIC	Small cell with at least one irregular edge
Drepanocyte	Sickle cell	Sickle Cell anemia	Crescent-shaped with dense center
Echinocyte	Burr cell	Renal failure (indicates very severe failure); often an artifact	Numerous regular scalloped projections evenly distributed
Acanthocyte	spur cell	Abetalipoproteinemia end-stage liver disease	A few irregular spiny projections unevenly distributed on membrane of a cell with reduced volume

Red Cell Inclusions

Name	Nature	Significance	Description
Coarse basophilic stippling	Residual RNA	Abnormal erythropoiesis seen in lead poisioning	Small to medium size purple granules diffusely distributed in RBC
Fine basophilic stippling	Residual RNA	Premature release of young RBC	Fine purple granules diffusely distributed in RBC
Howell-Jolly body	DNA remnant	Ineffective or absent spleen; erythroblast nuclear abnormality	One or two medium to large round purple granules in RBC
Siderotic granules (Pappenheimer bodies)	Nonhemoglobin iron	Ineffective or absent spleen; erythroblast nuclear and/ or cytoplasmic abnormality	Cluster of small purple granules in localized area of RBC or 1-2 medium or large size granule
Malaria parasite	Parasite	Malaria	Ring form with 1 or 2 purple chromatin dots and light blue cytoplasm, gamete forms sometimes present
Babesia parasite	Parasite	Babesiosis	Small, ring-shaped with filmy blue cytoplasm and one or more purple chromatin granules or a tetrad of tiny dot-like dark staining granules
Erythroblast (nucleated RBC)	Normal marrow cell	Abnormal in blood other than newborn	8-12mm cell with gray or orange cytoplasm and dense nucleus