Extracorpuscular Hemolytic Anemias Flashcards by Richen Basig

Classifications of hemolysis

acute vs chronic
inherited vs acquired
intravascular vs extravascular
intracorpuscular vs extracorpuscular (intrinsic vs extrinsic)

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acute

rapid onset, shorter time course

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chronic hemolysis

slow, with compensation from bone marrow

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premature destruction of structurally and functionally normal RBCs due to mechanisms outside of the RBCs

extracorpuscular hemolytic anemia

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Causes of Intracorpuscular Hemolysis

membrane defects
enzyme defects
hemoglobinopathies
PNH

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Causes of Extracorpuscular Hemolysis

non-immune causes: microangiopathic hemolytic anemias, infectious agents, mechanical forces
immune causes: alloimmune hemolytic anemias, autoimmune hemolytic anemias

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caused by a condition that leads to physical or mechanical RBC damage

non-immune hemolytic anemias

- microangiopathic, macroangiopathic

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abnormalities in the microvasculature

microangiopathic

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abnormalities in the heart or large blood vessels

macroangiopathic

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two other causes on non-immune hemolytic anemias

infectious agents

- chemical and physical agents: chemicals, drugs, venom, thermal injury

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microangiopathic hemolytic anemia

intravascular hemolysis = RBC fragmentation

- thrombocytopenia

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thrombotic microangiopathies (TMAs)

damage occurs when RBCs quickly pass through turbulent areas of small blood vessels partially blocked by microthrombi
combination of MAHA and thrombocytopenia in the appropriate clinical setting

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PBS Morphologies of MAHAs and TMAs

keratocytes (horn cells)
helmet cells
triangulocytes
microspherocytes

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Top 4 scary microangiopathic hemolytic anemias

thrombotic thrombocytopenic purpura
hemolytic uremic syndrome
disseminated intravascular coagulation (DIC)
HELLP syndrome

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What causes thrombotic thrombocytopenic purpura?

a deficiency of ADAMTS13

- protease responsible for cleaving ‘ultra-large’ multimers of von Willebrand Factor, which are involved in coagulation

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ULVWF can trigger this

inappropriate clotting which leads to ischemia

this causes RBC fragmentation and trapping of platelets

TTP = results in hemolysis, severe thrombocytopenia

- neurologic dysfunction, fever, and renal failure may also occur

Peripheral smear findings of TTP

schistos and polychromasia

urinalysis of TTP

protein, RBCs, casts if extensive renal damage

- Tx: plasma exchange

AKA ‘hamburger disease’

hemolytic uremic syndrome

Hemolytic Uremic Syndrome

caused by bacterial toxins (Shiga) - stimulates microvascular thrombi
presents w acute gastroenteritis and bloody diarrhea
damage to glomerular endothelial cells => acute renal failure
Tx: fluid replacement, renal support (why not antibiotics?)

~10% are atypical HUS that have other causes

inappropriate complement activation

HELLP Syndrome

hemolysis, elevated liver enzymes (transaminases), and low platelet count
complication in some pregnancies, correlation w pre-eclampsia, and eclampsia

the inappropriate activation of the coagulation system results in clots throughout the microvasculature

DIC

organ damage and bleeding
many causes: malignancies, infections, acute leukemias, obstetric complications, tissue damage, transfusion rxns, venoms, etc.

Mechanical causes of MAHAs

- prosthetic cardiac valves - circuits (ECMO) - vascular malformation - malignant hypertension - exercise (or hobby-induced hemoglobinuria)

immune hemolytic anemia

- shortened red cell survival due to an Ab-mediated mechanism > autoimmune: Ab specificity against one's pwn RBC antigens > alloimmune: Ab specificity against RBC antigens of another person > drug-induced: multiple mechanisms

autoimmune hemolytic anemia

- can be some complement activation - results from immune system dysregulation + loss of immune tolerance, exposure to antigen similar to self, etc - if all of complement cascade is fixed to RBC => intravascular cell lysis - if complement is only partially fixed = macs recognize Fc receptor of Ig and/or C3b complement - phagocytose RBC = extravascular RBC destruction

if all of complement cascade is fixed to RBC vs if complement is only partially fixed

- if all of complement cascade is fixed to RBC => intravascular cell lysis - if complement is only partially fixed = macs recognize Fc receptor of Ig and/or C3b complement - phagocytose RBC = extravascular RBC destruction

most common type of autoimmune hemolytic anemia

warm autoimmune hemolytic anemia

antibody characteristics of warm autoimmune hemolytic anemia

- most are IgG - react best at 37 degrees C - may fix complement (but only up to C3) - idiopathic cause (unknown) - secondary WAIHA (~70%) - Tx: steoids, splenectomy

cold autoimmune hemolytic anemia

- Ab characteristics = IgM, optimal reactivity at lower than 30 degrees C (~4C), and can bind complement - fix entire complement cascade - leads to the formation of membrane attack complex => RBC lysis in the vasculature - typically only complement found on cells - primary CAIHA = cold agglutinin disease - secondary '' (90%) = mycoplasma pneumonia infection, viral infections (mono)

lab findings for autoimmune hemolytic anemia

- decreased Hb - increased retics - increased serum bilirubin, lactate dehydrogenase - decrease haptoglobin - PBS: poly, spherocytes +/- agglutination

direct Ab test for autoimmune hemolytic anemia

- determines if RBCs are coated with Abs or complement | - can help to establish immune cause for hemolysis

Alloimmune hemolytic anemia

- hemolytic transfusion rxns | - hemolytic disease of the fetus and newborn

hematologic emergencies

- microangiopathic hemolytic anemia (> or equal to 1+ schisto) - suspected hemolytic anemia with > 1+ sphero