Hemolytic Anemias

• Hemolytic anemias share the following features:

- A shortened red cell life < 120 days

- Elevated erythropoietin levels (compensatory increase in erythropoiesis)

- Accumulation of hemoglobin degradation products (red cell hemolysis)

Extravascular hemolysis (within phagocytes): m.C Cause: RBCs deformability sequestration/phagocytosis

Splenomegaly (hyperplasia of phagocytes) Anemia Jaundice (unconjugated bilirubin) Tx: splenectomy

Intravascular hemolysis:

Less common

Cause:

mechanical injury (cardiac valves, thrombotic narrowing of the Microcirculation, repetitive physical trauma ) complement fixation

intracellular parasites

exogenous toxic factors (clostridial sepsis/release ofenzymes that digest the red cell membrane)

Anemia hemoglobinemia hemoglobinuria hemosiderinuria jaundice (unconjugated bilirubin)

Lysed RBCs---- free hemoglobin------haptoglobin------phagocytes

If haptoglobin ------free hemoglobin/ methemoglobin------ Red-brown urine

No splenomegaly

MORPHOLOGY:

erythroid precursors (normoblasts) in BM

prominent reticulocytosis in the p. blood

Erythropoietin

Hemosiderosis (accumulation of the iron containing pigment hemosiderin, particularly

in the spleen, liver, and bone marrow)

Extramedullary hematopoiesis (liver, spleen, and lymph nodes)----- Anemia

pigment gallstones (cholelithiasis)----- biliary excretion of bilirubin

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Sticky Note

Reticulucyte percentage should be from 1-2%,more tha that will be reticulocytosis which is a sign of bone marrow hyperplasia to compensate the anemia

Hereditary Spherocytosis

autosomal dominant

defects in RBC membrane skeleton---spheroid RBCs---- less deformable ----splenic sequestration/destruction

HS is caused by diverse mutations that lead to an

insufficiency of membrane skeletal components.

• Young HS red cells are normal in shape, but the destabilized lipid bilayer sheds membrane fragments as red cells age in the circulation.

• the life span of the affected red cells is decreased on average to 10 to 20 days from the normal 120 days.

• MORPHOLOGY:

Spherocytosis ----------- destinctive but not pathognomonic

Other features of hemolytic anemias

Moderate splenic enlargement (500-1000 gm)

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compact\spheroid\no central pallar

• Clinical Features:

family history

RBCs---hypotonic salt solutions---osmotic lysis (influx of water) mean cell hemoglobin concentration (dehydration loss of K+ H2O)

If compensated by erythropoiesis----------- asymptomatic

If decompensated-----hemolytic anemia--- Splenomegaly Anemia Jaundice

• aplastic crises ---- acute parvovirus infection.

• Hemolytic crises----intercurrent events leading to increased splenic destruction of red cells (e.g., infectious mononucleosis)

• Gallstones

• Splenectomy treats the anemia and its complications

Glucose-6-Phosphate Dehydrogenase Deficiency

• X-linked trait

• Hemolytic disease due to red cell enzyme defect (G6PD)----- antioxidant enzyme

• hemolysis result in misfolding of the protein, making it more susceptible to proteolytic degradation

Several hundred G6PD genetic variants are known, but most are harmless.

clinically significant variants:

• G6PD− : 10% of American blacks

• G6PD Mediterranean: in the Middle East

Reduced half-life of G6PD

G6PD activities fall quickly to levels inadequate to protect against oxidant stress as red cells age.

Episodic hemolysis is characteristic

Intravascular and extravascular hemolysis

exposures that generate oxidant stress. The most common triggers ar: infections ---- oxygen-derived free radicals/activated leukocytes

Drugs ---- antimalarials , sulfonamides, nitrofurantoins

certain foods ---- fava bean “Favism”

Morphology:

Heinz bodies (denatured globin forming membrane bound

Precipitates/inclusions)

Bite cells ( when macrophages pluck out the Heinz bodies in spleen)

spherocytes

• Clinical features: Acute intravascular hemolysis Anemia --- hemoglobinemia ---- hemoglobinuria begins 2 to 3 days following exposure of G6PD-deficient individuals to oxidants. greater G6PD Mediterranean variant. Because only older red cells are at risk for lysis, the episode is self-limited Intermittent hemolysis (not chronic) --- No splenomegaly No cholelithiasis

Sickle Cell Disease

common hereditary hemoglobinopathy

Mainly in individual of African descent

point mutation in the sixth codon of β-globin--- replacement of a glutamate residue with a

valine residue.

• Normal adult red cells:

contain mainly HbA (α2β2)

small amounts of HbA2 (α2δ2)

fetal hemoglobin (HbF; α2γ2)

• sickle cell trait: heterozygous for HbS (HbS:40%, HbA:60%)

Asymptomatic

do not sickle except under profound hypoxia

• sickle cell disease: homozygous for HbS

Symptomatic

• Pathogenesis:

HbS molecules undergo polymerization when deoxygenated.

Chronic hemolysis

Microvascular occlusions

Tissue damage

• Several variables affect the rate and degree of sickling:

- Interaction of HbS with the other types of hemoglobin in the cell:

HbA ---- HbS polymerization ---- heterozygous

HbF ---- HbS polymerization---- infants >5 or 6 months of age

HbC ---- Lysine/ Glutamate ------- milder, HbSC (50%, 50%)

- Mean cell hemoglobin concentration (MCHC):

MCHC ---- intracellular dehydration ---- sickling/polymerization

MCHC ---- α-thalassemia ----- sickling/polymerization

- Intracellular Ph:

Ph ----- O2 affinity ---- sickling

- Transit time of red cells through microvascular beds

If slow --- sickling ---- spleen, BM, inflamed tissue

extravascular hemolysis (mainly)

intravascular hemolysis

Microvascular occlusion

sickle cells express adhesion molecule so sticky

• MORPHOLOGY:

sickled cells

reticulocytosis

target cells (red cell dehydration)

Howell-Jolly bodies (small nuclear DNA remnants)/asplenia

BM is hyperplastic as a result of a compensatory erythroid hyperplasia.

bone resorption and secondary new bone formation, resulting in prominent cheekbones

• Childhood----spleen is enlarged up to 500 gm • Adolescence/early adulthood ---- splenic

infarction, fibrosis (autosplenectomy).

• Infarctions caused by vascular occlusions can occur in many other tissues as well, including the bones, brain, kidney

• In adult patients, vascular stagnation in

subcutaneous tissues often leads to leg ulcers

• Clinical Features: Vaso-occlusive crises/ pain crises: Infection/dehydration/acidosis---in most instances no predisposing cause is identified. bones, lungs, liver, brain, spleen, and penis. hand-foot syndrome or dactylitis of the bones of the hands or feet, Acute chest syndrome (fever, cough, chest pain, and pulmonary infiltrates)– fatal Priapism loss of visual

In children, painful bone crises are extremely common and often difficult to distinguish from acute osteomyelitis The most common cause of patient morbidity and mortality

Sequestration crises:

Massive entrapment of sickle red cells---rapid splenic enlargement----hypovolemia---shock----fatal-----treatment with exchange transfusions.

Aplastic crises:

parvovirus B19--- -erythropoiesis----anemia.

• Chronic hypoxia is responsible for a generalized impairment of growth and development, as well as organ damage affecting the spleen, heart, kidneys, and lungs.

• Increased susceptibility to infection with encapsulated organisms

• Pneumococcus pneumoniae and Haemophilus influenzae septicemia and meningitis are common, particularly in children, but can be reduced by vaccination and prophylactic antibiotics

• Diagnosis:

mixing a blood sample with an oxygen-consuming reagent, which induces sickling of red cells.

Hemoglobin electrophoresis.

Prenatal diagnosis is possible by analysis of fetal DNA obtained by amniocentesis or chorionic biopsy.

• About 90% of patients survive to age 20, and close to 50% survive beyond the fifth decade

• Treatment:

Blood transfusion

Antibiotics

Bone marrow transplant

Hydroxyurea (DNA inhibitor) : + HbF

Thalassemia Syndromes

• inherited mutations that decrease the synthesis of either the α-globin or β-globin chains that compose adult hemoglobin, HbA (α2β2)

• endemic in the Mediterranean basin, the Middle East, tropical Africa, the Indian subcontinent,

β-Thalassemias

• mutations that diminish the synthesis of β-globin chains.

• more than 100 different causative mutations, mostly consisting of point mutations

• two β chains are encoded by a single β-globin gene on chromosome 11

• β0 mutations: absent β-globin synthesis

• β+ mutations: reduced β-globin synthesis

• Impaired β-globin synthesis results in anemia by two mechanisms:

1- The deficit in HbA synthesis produces underhemoglobinized hypochromic, microcytic red cells with subnormal oxygen transport capacity.

2- diminished survival of red cells and their precursors. α chains precipitate within red cell precursors, forming insoluble inclusions----membrane damage----- apoptosis ---- ineffective erythropoiesis

insoluble inclusions----membrane damage----- sequestration---- extravascular hemolysis

• erythroid hyperplasia in the marrow

• Extensive extramedullary hematopoiesis

• skeletal abnormalities

• extraosseous masses in the thorax, abdomen, and pelvis.

• excessive absorption of dietary iron/due to -hepcidin

• secondary hemochromatosis

• β-Thalassemia Major:

Anemia---6 /9 m after birth---switches HbF-HbA

Hb: 3 to 6 gm/dL

RBCs: lack HbA (β0/β0) or small amounts (β+/β+ or β0/β+)

HbF: The major RBCs Hb

HbA2: normal, low, high

• MORPHOLOGY: Anisocytosis poikilocytosis Microcytosis Hypochromia Target cells Basophilic stippling fragmented red cells enlargement of the spleen The liver and the lymph nodes can also be enlarged by extramedullary hematopoiesis. new bone formation

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hypochromatic cells (pale)due to low HB

• clinical course:

Untreated children suffer from growth retardation and die at an early age from the effects of anemia.

cheekbones and other bony prominences are enlarged and distorted.

• With transfusions and iron chelation, survival into the third decade is possible

• BM transplantation is the only therapy offering a cure

• Cardiac disease resulting from progressive iron overload and secondary hemochromatosis

• β-Thalassemia Minor:

More common

Asymptomatic or mild anemia

HbA2 (4-8%)

HbF : normal or slightly increased

α-Thalassemias

• inherited deletions that result in reduced or absent synthesis of α-globin chains

• The two α chains in HbA are encoded by an identical pair of α-globin genes on chromosome 16,

• Newborns----γ4 tetramers--hemoglobin Barts • older children/adults---β4 tetramers---HbH---

more in Asian high affinity for O2 so not useful for O2 delivery

• hemolysis and ineffective erythropoiesis are less severe than in β-thalassemias because free β and γ chains are more soluble than free α chains and form fairly stable homotetramers

• HbA2: normal or low

Paroxysmal Nocturnal Hemoglobinuria

• acquired mutations in the phosphatidylinositol glycan complementation group A gene (PIGA), an enzyme that is essential for the synthesis of certain membrane-associated complement regulatory proteins (GBI=glycosylphosphatidylinositol)

• PNH blood cells are deficient in three GPI-linked

proteins that regulate complement activity: (1) CD55 (2) CD59 (3) C8 binding protein. Of these

• Red cells deficient in these GPI-linked factors are abnormally susceptible to lysis or injury by complement.

intravascular hemolysis: paroxysmal and nocturnal (–PH/+complement) in only 25% of cases; chronic hemolysis without dramatic hemoglobinuria is more typical.

Anemia

Venous thrombosis (platelet dysfunction)

Acute leukemia/MDS (Hematopoietic stem cells)

• diagnosed by flow cytometry (CD59, CD55)

• Tx:

C5 inhibitor therapy

Immunosuppressive drugs

BM transplantation

Immunohemolytic/autoimmune hemolytic Anemias

• caused by antibodies that bind to red cells, leading to their premature destruction.

• direct Coombs antiglobulin test

Patient’s RBCs with sera AB

• indirect Coombs antiglobulin test

Patient’s serum with RBCs/Ag

• Warm Antibody Type:

M.C

Extravascular hemolysis,

Tx: removal of initiating cause, immunosuppressive therapy, splenectomy

• Cold Agglutinin Type:

Finger, nose, ears---- vascular occlusion---pallor, cyanosis, Raynaud phenomenon

Hemolysis