Extracorpuscular Hemolytic Anemia

Intravascular vs Extravascular Hemolysis Clinical Results

1. Plasma free Hb

2. Haptoglobin

3. Hemoglobinemia

4. Hemoglobinuria

5. Hemosiderinuria

6. LDH

7. Indirect bilirubin

8. Urobilinogen

9. Splenomegaly

Finding	Intravascular hemolysis	Extravascular hemolysis
RBC destruction	Inside blood vessels	Mainly spleen/liver macrophages
Plasma free Hb	↑↑	Normal or slight ↑
Haptoglobin	↓↓↓	Normal or mildly ↓
Hemoglobinemia	Present	Usually absent
Hemoglobinuria	Present	Usually absent
Hemosiderinuria	May be present	Absent
Lactate dehydrogenase (LDH)	↑↑↑	↑
Indirect/Unconjugated bilirubin	↑	↑↑
Urine bilirubin	Usually negative for intact Hb; urine dipstick detects Hb	Usually negative
Urobilinogen	↑	↑
Splenomegaly	Usually less prominent	Common
Peripheral smear	Schistocytes may occur depending on cause	Spherocytes can occur
Main Hb breakdown site	Plasma → kidney/liver	Macrophages → spleen/liver

Classical Pathway {Trigger Condition}

1. Triggers when Igs bind to microbial Ags and the Fc region is opened

2. C1q binds Fc region to activate C1r & C1s

3. C1s cleaves both C4 & C2

4. IgG3 is the most efficient at activating complement, while IgG4 is not capable

Alternate/Properdin Pathway {Trigger Condition}

• Triggers when C3b (hydrolyze from C3) opsonizes the microbe (binds to factor b)

• Factor D then cleaves it into C3 convertase (C3bBb) and Ba

• Properdin stabilizes the C3 convertase

Lectin Pathway {Trigger Condition}

1. Initiates by mannose-bind lectin (MBL) attaches to mannose of microbes

2. MBL-associated serine proteases (MASP-1 & MASP-2) becomes activated

3. MASP-1 & MASP-2 performs similar job as C1s by cleaving C4 & C2

Intravascular Hemolysis

• Occurs from complete activation of the complement system where MAC is generated and lyse the RBC

• Cannot determined by decreased haptoglobin alone

Antibody-Dependent Cellular Cytotoxicity (ADCC)

• A mechanism where RBCs are opsonized with Ig1/Ig3/C3b/iC3b. Then the effectors cells FcR (recognized Igs) or complement receptor CR bind to RBCs

Hemoglobinuria vs Hematuria {Etiology}

	Hemoglobinuria	Hematuria
What is in urine?	Free hemoglobin	Intact RBCs
Source	Intravascular RBC destruction	Bleeding from urinary tract
Urine dipstick for "blood"	Positive	Positive
RBCs on urine microscopy	Absent or very few	Present
Plasma free Hb	↑	Usually normal
Haptoglobin	Often ↓	Usually normal
Classic association	Intravascular hemolysis	UTI, kidney stones, trauma, glomerular disease

Extravascular Hemolysis

• RBC destroyed by MPS of the spleen and liver

• Complement system can opsonize RBC with C3b/iC3b without MAC generation

• When partial phagocytosis occurs, RBC can repair itself by converting biconcave disk to a sphere-shape becoming spherocytes

Classification of Immune Hemolytic Anemia

• Alloimmune: patient produces alloantibodies to foreign red cell introduced through transfusions, pregnancy, transplants

• Autoimmune: autoreactive antibodies are not being destroyed and now directed against patient’s cells

• Drug-induced: antibodies directed at the red cells coated with the drug

Polyspecific DAT (Direct Antiglobulin Test)

Detect both IgG and complement (C3d, C3b) that are attached to the RBCs

Acute Hemolytic Transfusion Reaction {Intra/Extra}

• Associated with ABO blood group and intravascular hemolysis

• Involved IgM (group A & B) , IgG (group O), and IgA

• Must be monitored during transfusion because the reaction is immediate

• Administered IV fluid to prevent hemolyzed red cells from clogging the renal glomeruli

Delayed Hemolytic Transfusion Reaction {Intra/Extra}

• Most common type of transfusion reaction that is caused by IgG that are not ABO antigens

• Associated with extravascular hemolysis

• Post-transfusion, the Hct level is expected to rise by 3. Otherwise, it may due to hemolytic transfusion

Hemolytic Disease of Fetus Newborn (HDFN) {Intra/Extra}

• Only IgG can cross the placenta so only IgG is involved

• Associate with extravascular hemolysis

Warm Autoimmune Hemolytic Anemia

• Most common, accounts for 70% in adults

• Antibodies’ reactivity is optimal at 37 degree

• Positive for both IgG and C3D in 70% cases, 20% with only IgG

• Treat the present underlying disease. Otherwise corticosteroid → splenectomy → Rituximab (monoclonal antibody)