Hemolytic Anemias (RBC desturction)

What are hemolytic anemias? What RBC type will increase in PB? What does the lifespan of an RBC look like?

Anemias caused by increased RBC destruction → causes BM to accelerate production (retics will increase in PB)

RBC production is normal with very short lifespan → anemia develops b/c destruction is faster than RBC proliferation

What do RBCs usually look like in hemolytic anemias? What is the process called for premature RBC destruction?

RBCs will be normocytic, normochromic

• hemolysis

What 3 things classify the type of hemolytic anemia?

• Defect source: intrinsic or extrinsic to RBC

• Mode of onset (cause): inherited or acquired

• Location of hemolysis: intravascular or extravascular

Where does extravascular hemolysis occur? What will RBCs look like in PB?

RBCs are destroyed outside blood vessels (ex. in spleen, liver, BM) → macros in spleen & liver phagocytose RBCs

RBCs: spherocytes

Where does intravascular hemolysis occur? What will RBCs look like?

Defective RBCs destroyed as they circulate → lyse in circulation

RBCs: fragmented RBCs → schistocytes

What is the pathway of normal RBC destruction (catabolism) - due to old RBC?

Explain what happens to bilirubin - how does it leave the body?

Hemoglobin degraded (globin is returned to AA pool, iron separated & stored, heme ring (protoporphyrin) turns into bilirubin)

Bilirubin: considered unconjugated/indirect when it is made from broken-down protoporphyrin → secrets into plasma attached to albumin → enter liver & binds with 2 glucose molecules

• 2 glucose + bilirubin = conjugated/direct bilirubin

  • Direct/conjugated bilirubin: in liver → secreted as bile & enters GI tract → bacteria converts it to urobilinogen → majority excreted in stool, some in urine

What hemolysis is more common? Intravascular or extravascular? Is this destruction pathway any different from a normal old RBC death?

Common: Extravascular hemolysis (90% RBC destruction in spleen & liver)

• No, everything breaks down the same way

  • unconjugated/indirect Bilirubin → direct/conjugated bilirubin → urobilinogen → excreted

What increases in extravascular hemolysis and where? What is NOT present in extravascular hemolysis?

Increased:

• unconjugated bilirubin in serum

• urobilinogen in urine and stool

Not present:

• No hemoglobinuria, hemosiderinuira, free Hgb

What is the path of reabsorption of free Hgb that occurs in intravascular hemolysis (RBC destruction in blood vessels)?

What are two things that can be produced that indicates the kidneys have filtered a lot of free Hgb?

Intravascular hemolysis RBC: releases free Hgb into plasma & binds haptoglobin → free Hgb removed by liver & kidneys → in kidneys, Hgb is recycled

• Hemoglobinuria: excretion of free Hgb in urine b/c kidney could not keep up with large amount of free Hgb.

• Hemosiderinuria: indicates Hgb reabsorption occurring in renal tubules in b/c it converts into hemosiderin.

What increases in intravascular hemolysis? What else is present in the body due to intravascular hemolysis?

Increased

• unconjugated bilirubin

Present:

• Free Hgb in plasma

• Hemoglobinuria

• Hemosiderinuria

What is the normal Hgb concentration in plasma? What is the name of the anemia caused by excess free Hgb bound to haptoglobin?

Normal Hbg in plasma: 5mg/dL

Excess Hgb in plasma w/ haptoglobin: hemoglobinemia

What two types of hemolytic anemias are there? Where does the anemia occur in the RBC (intrinsic or extrinsic)? What are their subtypes?

• Hereditary hemolytic anemias → intrinsic & extravascular hemolysis

  • Membrane defects

  • Enzyme defects

• Acquired hemolytic anemias → extrinsic & extravas. or intravasc. hemolysis

  • Non-immune

  • immune

  • membrane defects

In general, what are signs of hemolytic anemia? What will the RBCs look like?

Signs:

• Jaundice (yellowing skin & eyes due to bilirubin)

  • Elevated unconjugated (indirect) bilirubin

• Gallstones (made of bilirubin)

• Dark/red urine due to plasma Hgb excretion

• Splenomegaly

• Reticulocytosis (more retics in PB)

RBCs: Normochromic, normocytic anemia

• Schistocytes (intravascular - in vessels hemolysis) or spherocytes (extravascular - in liver/spleen hemolysis)

Hereditary anemias happen intrinsically. What does this mean? What kind of hemolysis do the RBCs undergo?

Intrinsic: defects within an RBC (abnormality within an RBC themself)

• Undergo extravascular hemolysis → spleen/kidney pinches off abnormality

Acquired anemias happen extrinsically. What does this mean? What kind of hemolysis do RBCs undergo?

Extrinsic: defects caused by external agents (ex. something causes injury to RBC)

• Undergoes extravascular or intravascular hemolysis

Hereditary hemolytic anemias are intrinsic (internal RBC abnormality). They often undergo extravascular hemolysis.

What are the 2 types of membrane defects that can occur on an RBC?

What are the 2 enzyme defects? The 2 globin defects?

Membrane defects:

1. Hereditary spherocytosis

2. Hereditary elliptocytosis

Enzyme defects:

1. G6PD deficiency → extravascular & intravascular

2. Pyruvate Kinase deficiency

Globin defects:

1. Hemoglobinopathies

2. Thalassemias

One of the extravascular hereditary anemia defects is the membrane defect: Hereditary spherocytosis (HS).

What causes this defect and what does it result in the loss of?

What clears these cells from the body? In simple terms, what is the pathogenisis?

What are the 3 clinical findings of this?

Cause: inherited → Most common among white people

• deficiency of spectrin and/or ankyrin protein in membrane → loss of membrane b/c skeleton & bilayer disconnect due to lack of support proteins

  • Causes cells to become spherocytes

Cleared by: Spleen → spherocytes get stuck in splenic cords & become stressed from lack of ATP → Macros destroy stressed cells

• Pathogenesis: Spherocytes destroyed by Spleen → Anemia

Clinical: anemia, jaundice, splenomegaly

How will RBCs appear in extravascular hereditary spherocytosis (HS) anemia and how does it effect MCHC & retics?

Spherocytic → Normochromic, normocytic

• ↑ MCHC

• 8%+ Retics

What is the confirmatory test for extravascular hereditary spherocytosis (HS) anemia and how does it work? What is the treatment for this anemia and how does it effect the RBCs after?

Confirmatory test for HS: Osmotic fragility

• RBCs incubated in hypotonic NaCl solutions → spherocytes can’t expand as much as normal RBC → spherocytes hemolyze in high NaCl concentrations

  • Can be graphed to show degree of fragility in comparison to normal RBCs

Treatment: Splenectomy → b/c spherocytes won’t get removed so can still carry O2

• Howell-Jolly, target cells, and siderocytes may be present after removal

One of the extravascular hereditary anemia defects is the membrane defect: Hereditary elliptocytosis (HE).

What causes this defect, what % is asymptomatic and what does it cause RBCs to look like?

What percent of patients have this but don’t suffer from anemia?

What is the treatment of this anemia?

Cause: inherited, but 90% asymptomatic

• Deficiency in membrane protein: alpha-spectrin or beta-spectrin

  • Causes cells to be elliptocytes → Normochromic, normocytic

Treatment: nothing or splenectomy in symptomatic people

One of the extravascular/intravascular hereditary anemia defects is an enzyme defect: Glucose-6-phosphate dihydrogen deficiency (G6PD). What causes it and what gender is effected? Where does this deficiency occur most often in the world (3 places)?

Cause: inherited → X-linked recessive disorder; boys affected

• defect in hexose monophosphate pathway

Countries: Mediterranean area, Africa, China

Deficiency of enzyme G6PD causes extravascular/intravascular hereditary anemia. What is the functionality of G6PD? What is the pathogenesis of G6PD?

G6PD protects RBCs from oxidant damage & maintain Hgb → prevents hemolysis

Extravascular Pathogenesis: Hgb oxidized into methemoglobin → forms Heniz bodies → spleen “bites” out Heinz body → after picking, RBCs can also become spherocytes → can lead to Spleen fully removing RBCs

• Forms bite & blister RBCs

Intravascular Patho: Heinz body damage can be bad enough to cause RBC to hemolyze in circulation

Does G6PD deficiency always cause hemolytic anemia? If not, what can cause someone who is deficient to be at risk for hemolytic anemia?

Does not usually cause anemia.

• Exposure to: Infections, Oxidant drugs, or Fava beans increases oxidative stress on cell

  • If already deficient in G6PD which protects RBCs from this stress, cells will hemolyze (due to heinz bodies)

What test(s) or RBC appearance is checked to identify hereditary enzyme G6PD deficiency (usually seen during hemolytic attack)? What is the treatment for G6PD anemia?

Bite cells/blister cells → normochromic, normocytic

• Supravital stain → Heinz bodies

• ↑ Retic’s

• ↑ unconjugated bilirubin, hemoglobinuria (Hgb in urine), Hemoglobinemia (Hgb in plasma)

• Fluorescent spot test: lack of fluorescence = no G6PD

Treatment: Avoid exposure to oxidant drugs & fava beans

• Blood transfusions & treatment of infections

Another hereditary enzyme defect anemia is by deficiency of: Pyruvate Kinase (PK). Where is this anemia most common at? What causes this defect?

What is the clinical presentation?

Common anemia in: Northern European ancestry

Cause: Enzyme defect in Pyruvate Kinase

• problem in glycolytic pathway → decrease in ATP → low ATP = RBC membrane alterations → deformed/rigid RBCs are removed by spleen & liver

  • More severe than hemolytic spherocytosis (HS)

Clinical presentation: Jaundice, splenomegaly, ↑ gall stones (from indirect bilirubin)

What is the RBC presentation in Pyruvate Kinase Deficiency hemolytic anemia? What is the treatment?

RBCs: Normochromic, normocytic

• Hgb is 6-12 g/dL

• 2-15% Retic’s

• Reduced PK in quantitative assay

• ↑ indirect/unconjugated bilirubin

• No Heinz bodies

Treatment: Splenectomy, blood transfusions

Acquired hemolytic anemias can be non-immune caused and immune caused. What all causes non-immune acquired hemolytic anemias?

Non-immune: Diseases, intracellular organisms, chemicals, venoms, and drugs, burns

Non-immune hemolytic anemias (diseases, organisms, venoms/drugs, burns, pregnancy) can be extravascular or intravascular. Malaria causes what type of anemia? MAHA, Venom, and burns causes what type of anemia?

Malaria: Extravascular hemolysis

MAHA, venoms, burns: intravascular hemolysis

Microangiopathic hemolytic anemias (MAHAs) are non-immune intravascular hemolysis anemias. What happens to RBCs that causes this anemia? What are the 3 disorders that cause severe MAHA? Briefly describe the disorders.

Cause: RBC fragment as they pass through fibrin (clot) deposits inside small vessels → Fragmentation caused by the force (pressure) of the flowing blood

Disorders:

1. HUS (hemolytic-uremic syndrome): Multi-system disorder → RBC fragmentation, thrombocytopenia, acute nephrography and/or renal failure

2. TTP (Thrombotic thrombocytopenic Purpura): Syndrome of mechanisms → RBC fragmentation, thrombocytopenia, Neurological disfunction, progressive renal failure

3. DIC (Disseminated intravascular coagulation): Appears alongside birth complication, snakebite, heatstroke → RBC fragmentation & fibrin strands in PB, Thrombocytopenia, hemolysis not severe

Malaria is a non-immune extravascular hemolysis anemia. What causes it? How does it cause anemia (how is it extravascular)?

Caused by: malarial parasite → anopheles mosquito injects parasite → RBC nourishes parasite via iron in it

Extravascular: Ring stage grows into mature stages → spleen tries to pit out parasite → destroys parasite → non-infected RBCs become spherocytes

Venom is a non-immune intravascular hemolysis anemia. What causes it?

Brown recluse spider (or some snakes) injects venom → causes severe hemolytic anemia, necrosis, & ulceration

• Venom contains enzymes that acts on RBC membrane & produce lysis in circulation

Burns are a non-immune intravascular hemolysis anemia. What causes it?

3rd degree burns → severe acute hemolytic anemia

• Direct thermal to RBCs circulating in burned skin/tissue gets hemolyzed

  • Direct heat on RBC membrane damages spectrin → loss of elasticity & deformability

    • Schistocytes, spherocytes, acanthocytes

Acquired hemolytic anemias can be non-immune caused and immune caused. What are the 3 immune (Ab-Ag complex) hemolytic anemias (IHAs)? Include subtypes.

Immune hemolytic anemias:

1. Autoimmune (AIHA)

• Warm autoimmune hemolytic anemia

• Cold autoimmune hemolytic anemia

  • Paroxysmal cold hemoglobinuria

2. Drug-induced

3. Alloimmune (Ab’s from other people)

• Transfusion reactions

• Hemolytic disease of the newborn (HDN)

What causes immune hemolytic anemias? What will RBCs look like and what test is used to check for immune-mediated RBCs?

RBCs destroyed by immune mediated process (Ab or complement) → Damage occurs on surface of RBCs → removed extravascularly by macros and intravascularly if very bad damage

RBCs: normocytic, normochromic anemia

• spherocytes, schistocytes, polychromatophilia

• Retics

• Positive direct antiglobulin test (DAT)

What causes autoimmune hemolytic anemias (AIHAs)? Remember, what are the 3 forms? Which is the most common?

Cause: Auto-Ab’s target self RBC Ag’s

• Usually a secondary condition due to altered immunity state: ex. Lupus (SLE), Leukemia (CLL), Immunodeficiency disorders

3 forms:

• Warm autoimmune hemolytic anemia (WAIHA)

• Cold autoimmune hemolytic anemia

• Paroxysmal cold hemoglobinuria

Warm Autoimmune Hemolytic anemia (WAIHA) is an autoimmune anemia (AIHA). This is the most common AIHA. What causes it and what is usually the common Ab? What is the pathogenesis?

What will RBCs look like and what tests will be positive?

What is the treatment for it?

Cause: Warm reactive Ab → Usually by IgG

• Ab induces hemolysis at 37°C (Body TM)

• Anemia can be mild or severe

Pathogeneses: Extravascular hemolysis: IgG attaches to Ag on RBC → spleen macros “pick” out Ab-Ag complex → RBC becomes spherocyte → RBC phagocytosed in spleen by macros

• RBCs: spherocytes

Lab results:

• 5-10% retics & polychromasia

• ↑ unconjugated/indirect bilirubin

• Positive DAT (Coomb’s test)

Treatment: Prednisone, Splenectomy

Cold autoimmune hemolytic anemia (CIAHA - a.k.a cold agglutinin disease) is an autoimmune anemia (AIHA). This anemia makes up 16-30% of AIHAs. Who is usually affected? What causes it and what Ab is usually involved? What is the pathogenesis?

What will RBCs look like and what tests will be positive?

What is the treatment for it?

Affects: People 50+

Cause: cold reactive Ab → usually IgM

• Ab induces hemolysis at TM <32°C

• Chronic hemolytic anemia

Pathogenesis: Intravascular or extravascular hemolysis:

• IgM binds complement to RBC in cold environment → once warmed IgM releases but complement stays attached to RBC → Can cause intravascular hemolysis or initiate extravascular hemolysis

Lab:

• Polychromasia & retics

• Auto-agglutination of RBCs (especially at RT) → fix by warming at 32°C for 15 min

• ↑ unconjugated/indirect bilirubin

• Positive DAT

Treatment: Avoid cold exposure, move to warmer climates

Paroxysmal cold hemoglobinuria (PCH) is rare an autoimmune anemia (AIHA). This anemia makes up 30-40% of AIHAs in children. What 4 diseases is it usually associated with? What causes it (what Ab)? What is the pathogenesis?

Symptoms?

What will RBCs look like and what tests will be positive?

What is the treatment for it?

Diseases: EBV, Cytomegalovirus, measles & mumps

Cause: complement-binding IgG (Donath-Landsteiner Ab)

• Donath-Landsteiner Ab binds RBCs in Tm <15°C → upon warming Ab dissociates but complement activates → cell lysis (intravascular hemolysis)

• Ab induces massive hemolysis after cold exposure

Symptoms: pain in back & legs, cramps, headaches, chills & fever

Lab/RBC: Retics, spherocytes, hemoglobinuria & hemoglobinemia

• Weak + DAT for complement

• Elevated serum bilirubin

Treatment: avoid cold exposure, if severe - transfusions, if from infection = cure.

Moving away from autoimmune (AIHA) acquired immune anemias, another type of acquired immune hemolytic anemia (IHA) is caused by drugs.

Is this a common acquired anemia, and what are some drug types that can cause this anemia? What kind of hemolysis occurs in this anemia and what is believed to be the 2 potential pathogensis?

Not common in acquired anemias.

• Drugs: Antimicrobials, NSAIDs, Diuretics, Antidiabetic

2 possibilities:

1. Drug adsorption: drug binds to RBC → Ab produced against drug → Extravascular hemolysis via macrophages in spleen

2. Immune complex formation: drug binds w/ protein in plasma (Ag complex) → Ab produced against it → Complement activates → Intravascular hemolysis