Normocytic Anemia I (ExtraVascular Hemolysis)

Hemolysis is known to be

Increased Destruction → Has increased reticulocyte count

Can be classified as:

Causes: Intrinsic to RBC vs extrinsic to RBC

Location of hemolysis:

Intravascular and Extravascular

What are the features of all Hemolytic Anemias

Shortened RBC lifespan due to destruction

Reticulocytosis

Liberation of hemoglobin of degradation products

Increased unconjugated (Indirect) bilirubin = acholuric

jaundice (Jaundice without bilirubinuria)

Increased erythropoiesis → Normoblastic erythroid hyperplasia in marrow

Pigmented gallstones

Increased LDH

Decreased/No Haptoglobin

Features of Intravascular Hemolysis

Red cells lyse inside circulation and

release products into blood

Anemia

Reticulocytosis

Decreased Haptoglobin

Increased LDH

Increased Urine Urobilinogen

Plasma hemoglobin

Urine Hemoglobin

Urine Hemosiderin

Methemoglobinemia

DAT negative

Schistocyte

Features of Extravascular Hemolysis

Ingestion of RBCs by macrophages in liver, spleen and bone marrow

Anemia

Reticulocytosis

Decreased Haptoglobin

Increased LDH

Increased Urine Urobilinogen

Normal plasma hemoglobin

DAT positive

Spherocytes

Splenomegaly

Location of Extravascular Hemolysis

Liver, spleen, lymph node

Extravascular Hemolysis Is Caused By

Hereditary Spherocytosis

Sickle cell anemia

Hemoglobin C

Autoimmune hemolytic anemia (AIHA)

Thalassemias

Intravascular Hemolysis Is Caused By

Glucose-6-phosphate dehydrogenase (G6PD) deficiency

Paroxysmal nocturnal hemoglobinuria (PNH)

Malaria

Hemolytic Disease of the Newborn Microangiopathic/thrombotic hemolytic anemia

Hereditary Spherocytosis/Elliptocytosis

Autosomal Dominant

Defect of RBCs cytoskeleton-membrane connecting proteins → Ankyrin (band 3 protein, for spherocytosis) → Spectrin (band 4.2 protein, for elliptocytosis)

Cells becomes round → less capable to maneuver in the spleen

Eventually engulfed by spleen macrophages

Splenomegaly

***50% of people will get cholelithiasis due to pigmented gallstones***

Increased MCHC – not usually seen on other anemias !!!

Can have aplastic crisis with Parvovirus B19 infection

Pathophysiology of Hereditary Spherocytosis

Weakened interactions cause red cells to lose membrane fragments

Hereditary Spherocytosis/Elliptocytosis Histological Slides

Diagnosis of Hereditary Spherocytosis

Normocytic anemia (MCV 80-100)

Hemoglobin: Mildly reduced

MCH: Normal

MCHC: Increased*

Reticulocyte count: increased (>3%)

Peripheral smear → Red cells appear small and lack central pallor

Polychromasia and Nucleated RBC’s

– Confirmatory test

Osmotic fragility test

Clinical Features of Hereditary Spherocytosis

Triad of findings:

1. Anemia

2. Splenomegaly

3. Jaundice: due to increased unconjugated bilirubin.

Other findings:

1. Gall stones (calcium bilirubinate) → Due to increased concentration of conjugated bilirubin in bile

2. Aplastic crisis → May occur after parvovirus B19 infections

Consider diagnosis of HS:

FH of splenectomy

Increased incidence of gall stones (jet black calcium biluribinate stones)

Treatment of Hereditary Spherocytosis

Splenectomy (anemia is corrected but RBC defect and Spherocytes persist)

Must give vaccines following splenectomy to protect against sepsis from → S.pneumoniae and H.influenzae

Sickle Cell Anemia Leads To

Red cell distortion

Hemolytic anemia

Microvascular obstruction

Ischemic tissue damage

Sickle Cell Disease

10% of African-Americans carry the gene→ protective role against malaria

Homozygous: presence of 2 abnormal Beta genes (1 in 650 African Americans)

→ >90% HbS in RBCs

Sickle Cell Trait

Heterozygous: presence of 1 abnormal B gene resulting in < 50% HbS

Hb with

Pathogenesis of Sickle Cell Anemia

Deoxygenated HbS molecules undergo aggregation and

polymerization

Can occur through hypoxia, dehydration and acidosis

Process is reversible BUT repeated sickling stiffens RBC membranes, making cells more susceptible to hemolysis and can cause vascular obstruction

Hemoglobin F is protective (first 6 months) – newborns asymptomatic

Sticky cells in stacks can cause

Vaso-occlusion and lead to infarction

Features of Severe Hemolytic Anemia

Reticulocytosis - Increased retic count

Jaundice

Hyperbilirubinemia

Erythroid hyperplasia in bone marrow

Vaso-Occlusive Consequences

KNOW THESE!!!!!!!!!

Due to extensive and irreversible sickling

Dactylitis: infarction of small bones of the hand, more common in infants

Autosplenectomy: (infarcted, shrunken, fibrotic spleen)

Increased risk of encapsulated organisms → especially pneumococcal

(most common cause of death in infants)

Increased risk of Salmonella osteomyelitis or Salmonella pneumonia

Howell-Jolly bodies in peripheral smear

Acute chest syndrome:

Predisposed by pneumonia

(most common cause of death in adults)

Renal papillary necrosis

Continuation of Vaso-Occlusive Consequences

Pain Crisis – painful limbs, back, chest, abdomen often from infection or dehydration

Aseptic necrosis of femoral head Chronic Leg ulcers → **** Often used as a clinical finding ***

Risk of aplastic crisis – dramatic fall in hemoglobin from → parvovirus B19 viral infection → like spherocytosis

Massive erythroid hyperplasia causes crewcut appearance of skull and chipmunk facies

Factors Affecting Formation of Sickled RBC

1. The presence of hemoglobins other than HbS

2. The concentration of HbS in the cell

3. The length of time that red cells are exposed to low oxygen tension

Treatment:

Hydroxyurea → Increases concentration of Hemoglobin F

Blood Smear in SCD

Asplenia

Absence of spleen/absent splenic function

Increased risk of infection

Risk for Encapsulated organisms → Strep. Pneumonia

Sickle Cell Lab Findings

SCREEN TEST:

Metabisulfite: causes sickling with any amount of HbS (positive in both disease and trait)

Electrophoresis: presence, and amount of HbS

What are the lab findings for Sickle Cell Disease

>50% HbS, (usually >90%)

Some HbF and HbA2 (only few or NO HbA)

What are the lab findings for Sickle Cell Trait

>50% HbA

Hemoglobin Electrophoresis

Hemoglobin C

Glutamic acid is replaced by Lysine

When homozygous → HbC crystals seen on blood smear

Splenomegaly

Target cells

Note: Can have HS and HC combination

More sickling than HC alone

Prone to avascular necrosis of bone and proliferative retinopathy

Autoimmune Hemolytic Anemia

Hemolysis due to antibodies against antigens on RBC

surface

Classification:

1. Autoimmune HA

2. Drug induced HA

3. Alloimmune HA

1. Hemolytic transfusion reaction

2. ABO hemolytic disease of

newborn

3. Rh hemolytic disease of

newborn

Warm Agglutinins

AIHA→ rare cause of hemolysis precipitated by antibodies directed against blood group antigens

These antibodies are most commonly IgG, and react with proteins on the surface of red blood cells at normal body temperature

Cold Agglutinins

Autoantibodies that react with antigens on the red blood cell surface

They may induce complement-mediated hemolysis and agglutination of red cells

Can be precipitated following INFECTION in particular MYCOPLASMA PNEUMONIA organisms

IgG Mediated Disease: Warm Agglutinins

Binding occurs in the warm central part of the body

RBCs are coated with the antibodies - Splenic macrophages remove pieces of the RBC membrane including the antibodies → gradual loss of membrane and *** spherocytosis ***

Drugs attach to the membrane or induce autoantibodies

Treatment of Warm Agglutinins

Remove causing drug, IVIG, and splenectomy if necessary

IgM Mediated Disease: Cold Agglutinin

IgM binds to RBCs and fixes complement

Binding occurs in the relatively cold temperature of the extremities

Residual C3b serves as opsonin for splenic macrophages removing some of the membranes → eventual spherocytosis

Can be seen in mycoplasma infection and mononucleosis (EBV)

Extreme activation of complement by excessive antibodies can lead to intravascular hemolysis

DAT Test

Also called Coombs Test

Antibody mediated (IgG or IgM) destruction of RBCs

Used to test presence of RBC coated by the Ab/complement

Anti Ab/complement is added to blood If RBCs are coated → agglutination occurs → positive test

Indirect Coombs test:

Used to test presence of antibodies in patient’s serum

Anti-Antibodies are added to patient’s blood

If antibodies are present → agglutination occurs → positive test

Summary: Characteristics of Agglutinins