MLS 2304 Chapters 20–22: Hemolysis and RBC Disorders

What is the primary goal when studying RBC destruction?

To separate destruction from production failure and recognize major intrinsic RBC disorders.

What does a low reticulocyte count indicate in anemia?

A production problem.

What does an appropriate or high reticulocyte count suggest?

Blood loss or RBC destruction.

What is compensated hemolysis?

A condition where hemolysis occurs without anemia due to adequate marrow output.

What happens when RBC destruction exceeds marrow output?

Hemoglobin falls and anemia appears.

What are the markers of hemolytic disorder?

Reticulocytosis, increased LDH, increased indirect bilirubin, decreased haptoglobin, and compatible smear clues.

What distinguishes hemolytic anemia from a hemolytic disorder?

In hemolytic anemia, RBC destruction exceeds the marrow's ability to replace cells, leading to decreased hemoglobin and hematocrit.

What are the five descriptors used to classify hemolysis?

Time course, origin, defect location, site, and mechanism.

What is the difference between intravascular and extravascular hemolysis?

Intravascular hemolysis occurs in blood vessels, while extravascular hemolysis occurs in the spleen or liver.

What does increased LDH indicate in hemolysis?

Cellular breakdown.

What does increased indirect bilirubin indicate?

Heme catabolism.

What happens to haptoglobin during intravascular hemolysis?

Haptoglobin decreases as it binds free hemoglobin.

What are common findings in macrophage-mediated hemolysis?

Indirect bilirubin increases, and urobilinogen may also increase.

What is a typical morphology finding in hereditary spherocytosis?

Dense RBCs without central pallor.

What does the presence of schistocytes indicate?

Mechanical or fragmentation hemolysis.

What is the significance of reticulocytosis in hemolysis?

It supports marrow compensation in response to RBC destruction.

What does the term 'macrophage-mediated removal' refer to?

The process where macrophages remove RBCs, typically in the spleen or liver.

What is the role of morphology in diagnosing hemolysis?

Morphology suggests the mechanism but does not define it alone.

What does the term 'hemoglobinuria' indicate?

The presence of free hemoglobin in urine, often due to intravascular hemolysis.

What is the relationship between site and mechanism in hemolysis?

Site indicates where destruction occurs, while mechanism explains how RBCs are damaged or removed.

What is the importance of building a pattern in hemolysis diagnosis?

No single marker proves the whole mechanism; a pattern of markers provides stronger evidence.

What does a decrease in haptoglobin indicate?

It can indicate hemolysis, particularly if free hemoglobin is released into plasma.

What is the clinical significance of spherocytes in a blood smear?

They may indicate immune hemolysis or hereditary spherocytosis.

How can one differentiate between intravascular and extravascular hemolysis based on lab findings?

Intravascular hemolysis shows free hemoglobin in plasma, while extravascular hemolysis does not.

What should be assessed to confirm the cause of RBC removal in hemolysis?

Morphology and confirmatory tests.

What does the term 'hemolytic anemia' imply about RBC survival?

RBC survival is shortened due to destruction exceeding the marrow's replacement capacity.

What is the significance of the reticulocyte response in hemolysis?

It indicates whether the marrow is capable of compensating for RBC loss.

What can cause LDH and indirect bilirubin to rise without effective peripheral hemolysis?

Ineffective marrow production or breakdown markers from RBC destruction after release.

What does an increased reticulocyte count indicate?

It indicates a response to RBC loss or destruction.

What is intrinsic hemolysis?

A condition where the RBC itself has a survival problem due to internal defects.

What are some intrinsic mechanisms that can fail inside the RBC?

Membrane structure, oxidative defense, ATP generation, and deformability.

What is the significance of RBC deformability?

It allows RBCs to bend and squeeze through capillaries, affecting their survival.

What are vertical and horizontal membrane interactions?

Vertical interactions anchor the lipid membrane to the cytoskeleton, while horizontal interactions stabilize the cytoskeletal lattice.

What is hereditary spherocytosis?

A condition where membrane loss creates less deformable RBCs, leading to spherocyte formation.

What clinical patterns are associated with hereditary spherocytosis?

Chronic extravascular hemolysis, jaundice, splenomegaly, gallstone risk, and reticulocytosis.

What does a positive Direct Antiglobulin Test (DAT) indicate?

It indicates immune hemolysis, while a negative DAT suggests hereditary spherocytosis.

What is the role of EMA binding in diagnosing hereditary spherocytosis?

Decreased EMA binding supports a membrane-protein defect in hereditary spherocytosis.

What does osmotic fragility testing reveal in hereditary spherocytosis?

Increased osmotic fragility indicates that spherocytes tolerate hypotonic stress poorly.

What is the relationship between RBC shape and membrane function?

RBC shape can indicate which membrane function has failed, aiding in diagnosis.

What is paroxysmal nocturnal hemoglobinuria (PNH)?

An acquired intrinsic defect where RBCs lack surface complement protection due to a PIGA mutation.

Why is PNH considered an intrinsic defect?

Because the blood-cell clone lacks protective surface proteins, making it vulnerable to complement attack.

What are some broader hereditary membrane patterns to recognize?

Elliptocytes in hereditary elliptocytosis, ovalocytes in band 3-related rigidity, and stomatocytosis.

What does the term 'spherocyte' refer to?

A spherical RBC that is less deformable and often associated with hereditary spherocytosis.

What is the importance of reticulocyte count in hemolytic disorders?

It helps differentiate between successful compensation for RBC loss and inadequate marrow production.

What does a family history suggest in the context of hereditary spherocytosis?

It may support the diagnosis due to the genetic nature of the disorder.

What is the typical morphology seen in hereditary spherocytosis?

Spherocytes and polychromasia on the blood smear.

How does membrane loss affect RBCs in hereditary spherocytosis?

It decreases the surface area-to-volume ratio, leading to less deformability.

What is the clinical significance of indirect bilirubin and LDH levels in hemolysis?

Elevated levels indicate hemolysis and can help differentiate types of hemolytic anemia.

What are some common intrinsic defects leading to RBC survival issues?

Defects in membrane structure, oxidative defense, and metabolic pathways like glycolysis.

What does the term 'acquired intrinsic defect' refer to?

A defect that arises from an acquired mutation in a hematopoietic stem cell, such as in PNH.

How can morphology aid in diagnosing hemolytic disorders?

Morphological patterns on blood smears provide clues to the underlying mechanism of hemolysis.

What is the role of cytoplasmic viscosity in RBC survival?

It affects hemoglobin concentration and hydration, influencing the RBC's ability to withstand circulation stress.

What does PNH stand for?

Paroxysmal Nocturnal Hemoglobinuria

What are the three main clinical patterns of PNH?

Hemolysis, thrombosis risk, and marrow-failure overlap

What laboratory findings indicate intravascular hemolysis in PNH?

Markedly increased LDH, decreased haptoglobin, hemoglobinuria or hemosiderinuria

What is the significance of a negative DAT in PNH?

It suggests that hemolysis is not immune-mediated.

What is the key diagnostic test for confirming PNH?

Flow cytometry to demonstrate a GPI-deficient clone.

What role does G6PD play in red blood cells?

It protects RBCs from oxidative injury by maintaining NADPH levels.

What happens to RBCs when G6PD activity is decreased?

NADPH and reduced glutathione levels drop, leading to increased oxidative damage.

What triggers oxidant stress in G6PD deficiency?

Infections, certain drugs, and fava beans.

What are Heinz bodies?

Denatured hemoglobin precipitates that form in response to oxidative stress.

What is the morphology of bite and blister cells?

Cells that have undergone splenic pitting after oxidative injury.

What is a common laboratory trap in diagnosing G6PD deficiency?

A normal G6PD result during acute hemolysis may be misleading due to reticulocyte dominance.

What is the primary problem in Pyruvate Kinase deficiency?

Impaired ATP generation leading to decreased RBC membrane function and deformability.

What does a chronic nonspherocytic hemolysis pattern indicate?

It suggests a glycolytic ATP defect, often confirmed by PK activity testing.

What is the first step in the hemolysis decision path?

Determine if RBC destruction is occurring using reticulocyte count, LDH, and haptoglobin levels.

What does reticulocytosis indicate?

It suggests that the marrow is compensating for RBC destruction.

What is the importance of morphology in hemolysis diagnosis?

It provides clues about the type of hemolysis and directs further testing.

What confirms the mechanism of hemolysis?

Targeted tests such as DAT, EMA, flow cytometry, G6PD activity, or PK activity.

What is the role of splenic pitting in oxidative injury?

It removes altered membranes from RBCs, leading to the formation of bite and blister cells.

What is the relationship between oxidant exposure and G6PD deficiency?

Oxidant exposure reveals the vulnerability of G6PD-deficient RBCs by overwhelming their antioxidant defenses.

What does a high-sensitivity flow cytometry test assess in PNH?

It checks for the absence of GPI-linked proteins on blood-cell clones.

What is the clinical significance of unexplained thrombosis in PNH?

It may indicate the presence of a GPI-deficient clone and the risk of thrombosis.

How does the presence of reticulocytes affect G6PD testing results?

Reticulocytes may have higher G6PD activity, potentially masking deficiency.

What is the consequence of decreased ATP in RBCs?

Impaired membrane function and increased risk of hemolysis.

What does the term 'chronic nonspherocytic hemolysis' refer to?

A type of hemolysis characterized by a defect in glycolysis leading to RBC destruction.

What is the final step in diagnosing hemolytic disorders?

Naming the disorder should be the last step after confirming the mechanism.

What can destroy a normal red blood cell (RBC)?

Its environment, specifically through extrinsic nonimmune hemolysis.

What is the clinical question regarding RBC survival?

What external process is shortening RBC survival?

What are the initial steps to confirm RBC destruction?

Confirm destruction, inspect the film, and separate the causes.

What are the four external mechanisms that can shorten RBC survival?

Microangiopathic, macroangiopathic, infectious, and direct injury.

What is microangiopathic hemolytic anemia (MAHA)?

A condition where microvascular injury fragments RBCs.

What is a common clue for mechanical fragmentation in RBCs?

The presence of schistocytes and a specific platelet pattern.

What causes mechanical fragmentation in macroangiopathic hemolysis?

Valve shear or repetitive impact.

What does infectious hemolysis involve?

Lysis or accelerated clearance of RBCs due to intra-RBC organisms or toxins.

What is direct injury to RBCs?

Membrane injury caused by heat, chemicals, or venoms.

What is the significance of schistocytes in blood films?

They indicate fragmentation of RBCs but do not specify the cause.

What are the three evidence streams to follow in MAHA?

Platelet count, coagulation tests, and patient context.

What does a low platelet count suggest in MAHA?

Small-vessel thrombotic injury.

What is the role of ADAMTS13 in thrombotic thrombocytopenic purpura (TTP)?

ADAMTS13 deficiency permits the formation of platelet-rich microthrombi.

What are the two major pathways to hemolytic uremic syndrome (HUS)-associated kidney injury?

Shiga toxin-associated and complement-mediated pathways.

What does HELLP syndrome stand for?

Hemolysis, Elevated Liver Enzymes, Low Platelets.

What are the laboratory findings in HELLP syndrome?

Increased LDH, elevated AST/ALT, and decreased platelet count.

What triggers disseminated intravascular coagulation (DIC)?

Systemic triggers such as sepsis or trauma.

What are typical laboratory findings in DIC?

Decreased platelets, prolonged PT/aPTT, decreased fibrinogen, and increased D-dimer.

What is the importance of integrating clinical context in MAHA diagnosis?

To narrow down the cause based on the laboratory pattern and clinical findings.

What is the clinical significance of microthrombi in MAHA?

They indicate vessel injury and can lead to mechanical shear of RBCs.

What is the role of coagulation tests in diagnosing MAHA?

To assess factor consumption and help identify the underlying cause.

What is a common result of both TTP and HUS?

Microvascular RBC fragmentation, low platelets, and kidney injury.

What does the term 'mechanical mimic' refer to in MAHA?

A situation where preserved platelet counts suggest a non-thrombotic cause of fragmentation.