Pincez Pathophysiologies of RBCs (L7) Flashcards
What informations do automated blood cell counters provide us with?
(ex: flow cytometry?)
What is the good old alternative?
- Count for each cell type: RBC, platelets white blood cells
- Differential of wbc (i.e. subtypes: neutrophils, lymphocytes)
- Several erythrocytes parameters:
- Hemoglobin concentration (g/L)
- Mean corpuscular volume (MCV) = hematocrit/rbc count (fL)
- Reticulocytes (g/L) = rbc precursors → marker of RBC production
Good old method = let the blood sediment in a tube and measure the hematocrit
How do reticulocytes appear in the microscope?
They appear more blue/purple because they still have RNA
- center is less pale
What different part of RBC morphology can be indicative of disorders?
- Size variations
- Hemoglobin distribution (very thin outside)
- Shape variation (Sickle cell, Burr cell/dehydrated, elongated, spheric)
- Inclusions of other organelles
- Agglutination/Rouleaux
- Crystal formation
What is the difference between looking at normal bone marrow vs peripheral blood?
Bone marrow → different blood cell precursors
Peripheral blood → only mature forms of the cells (mostly RBCs)
How does Hemoglobin concentration in the blood vary throughout life?
What is the normal range for male vs females?
Very high in neonates → goes down quickly in first 3 months → gradually ramps back up to reach steady state ~20 years old
Hemoglobin (Hb) concentration:
120 – 155 g/L (adult females)
140 – 175 g/L (adult males)
What is the normal hematocrit (Ht) range for male vs female adults?
Total volume of rbc/total blood volume:
34.9-44.5% (adult females)
38.8-50.0% (adult males)
*Ht and Hb are highly correlated
What are the 2 main sites of destruction of erythrocytes?
Liver and Kidney
Which diseases are related with bone marrow failure (aplastic anemia)?
Constitutional (genetic):
- Fanconi anemia (susceptibility to DNA damage) → lack of DNA replication due to the damage
- Dyskeratosis congenita (telomere maintenance failure) → quickly children can’t produce enough blood cells because the telomeres are too short
Acquired:
- Immune (idiopathic)
- Toxic (drug or radiation-induced)
- Infection
Tumoral bone marrow (Leukemia) → tumor cells take up all the space, noe more space for normal hematopoietic cells (see a lack of diversity un the microscope)
*Not specific to erythrocytes, all hematopoiesis is affected
What are the 3 main phases of erythrocyte synthesis?
- Ribosome synthesis
- Hemoglobin synthesis
- Nuclear and organelles extrusion
2e6 RBCs produced/second
- main component of mature erythrocytes = hemoglobin
What factor can be the cause of anemia at the different levels listed below:
1. DNA
2. Ribosomes
3. Globin chains
4. Fe2+
5. Porphyrin
6. Heme
7. EPO (hormonal stimulus)
the different levels listed below:
1. DNA → B9/B12 vitamine deficiency impairs replication
2. Ribosomes → Diamond-Blackfan anemia (can’t translate enough GATA1 or globin chains)
3. Globin chains → Thalassemia
4. Fe2+ → Inflammation or Iron deficiency
5. Porphyrin → Porphyria
6. Heme → Sideroblastic anemias
7. EPO → Chronic kidney disease
What part of erythrocyte synthesis can explain polycythemia/erythrocytosis?
Increase in EPO secretion from the kidney
What is primary vs secondary polycythemia?
Primary = Defect in the bone marrow (EPO-independent)
Secondary = Defect in the kidney → secrete higher levels of EPO
What can be the different causes of Secondary polycythemia?
ELEVATED EPO LEVELS
- Constitutional (germline) genetic variants leading to augmented hypoxia sensing => Inappropriate activation of EPO transcription (i.e. even in normoxia)
- Variants in VHL, EPAS1 (HIF-1a), EGLN1 (PHD2, which degrades HIF-1α) - Chronic hypoxia due to high altitude => Appropriate activation of EPO transcription (physiological)
- Chronic hypoxia due to cardiopulmonary disease or smoking => Appropriate activation of EPO transcription
- Chronic pulmonary disease, Sleep apnea, Smoking
- Cyanotic heart disease - Local chronic hypoxia due to kidney disease => Appropriate activation of EPO transcription
- Arterial stenosis, Kidney disease (hydronephrosis, cysts) - Secretion of EPO by tumors (hepatocellular carcinoma, renal cell carcinoma, hemangioblastoma…) => Ectopic activation of EPO transcription (non-regulated)
What is the main cause of Primary polycythemia?
Polycythemia vera
Polycythemia vera (PV), the most frequent type of myeloproliferative neoplasm (MPN). Somatic mutation in JAK2 kinase (V617F) most common
Result in constitutive (EPO-insensitive) activation of downstream STAT (promotes differentiation)
=> Polycythemia
What are the 2 main/general types of anemias?
Non-regenerative (low RET):
- Problem in the production of RBCs
1) Microcytic (low MCV)
2) Normo/Macro-cytic
Regenerative (high RET)
- Problem in the destruction of RBCs
1) Non-hemolytic
2) Hemolytic → Intracorpuscular or Extracorpuscular
What can be causes of Non-regenerative Microcytic anemias?
How do these cell appear in the microscope?
Microcytic = low MCV + low RET
- Iron deficiency (poïkylocytosis = abnormal shape)
- Thalassemia (globin chains) → normal iron, target cells (Hb small circle in the center)
- Sideroblastic anemia → normal iron, cells have dark spots of iron in them as it is not incorporated into heme
Can diagnose in the microscope seing low hemoglobin content → thick edges get very thin
What can be causes of Non-regenerative Normo or macrocytic anemias?
Normal or high MCV, low RET
- Chronic kidney disease
- Blackfan Diamond anemia
- B9/B12 deficiency
Other causes…
What can be causes of Regenerative Non-hemolytic anemias?
*high RET
Non-hemolytic = not related to destructions of RBCs
Cause = Acute Bleeding
What can be causes of Regenerative Hemolytic Intrcorpuscular anemias?
High RET, High RBC destruction
- Membranopathies
- Hemoglobinopathies
- Enzymopathies
What can be causes of Regenerative Hemolytic Extracorpuscular anemias?
High RET, High RBC destruction
- Autoimmune hemolytic anemia
- Mechanical
- Infection
What are the 2 mechanisms of erythrocyte destruction?
Extravascular (physiological, but pathological when too much):
Physiological < 1% of RBCs
1. RBC is phagocytosed by macrophage in the kidney/liver and broken back in 1 of the 3 main components
2. Protoporphyrin turned into bilirubin → liver and excreted in urine
Intravascular (pathological):
- Contents are released in the bloodstream → Hb goes to the kidney → urine (change in color)
What are clinical indicators of hemolysis?
- Icterus (jaundice)
- Splenomegaly if extravascular (macrophages destroying the RBCs are mainly in the spleen → spleen gets really big
- Red urine if intravascular
What are biological consequences of hemolysis?
*Regenerative anemia (high RET)
- Increased unconjugated bilirubin
- Increased lactate dehydrogenase
What are the intracorpuscular hemolysis mechanisms?
*Defect of the RBC
Membrane:
- Congenital membrane defects
- Paroxysmal nocturnal hemoglobinuria
Hemoglobin: (acquired)
- Thalassemia
- Sickle Cell Disease
Enzymes:
- G6PD deficiency
- Pyruvate kinase deficiency
What are the extracorpuscular hemolysis mechanisms?
Immune:
- Autoimmune hemolytic anemia
Mechanic:
- Thrombotic microangiopathy
- Cardiac valves
- Thermal injury
Infection:
- Malaria
What is hereditary spherocytosis?
A membranopathie → intracorpuscular hemolysis
Membrane → phospholipid bilayer closely linked to cytoskeleton
Problem: lack of link between cytoskeleton and membrane → loss of pieces of membranes
Spherocytes have lost a small volume and a large surface → decreased surface/volume ratio → more spherical shape → splenic sequestration → increase contact with macrophages → phagocytosis
*Cytoskeleton made of a-spectrin and b-spectrin
What confers deformability to RBCs?
- High surface/volume ratio
- Low intracellular viscosity
- Healthy membrane
*Disk shape, not spheric
What is the best treatment for hereditary spherocytosis?
Splenectomy
But increase risk of encapsulated bacteria fatal infections, thrombosis and possibility cancer
Because spherical RBCs get seuqestered in the spleen
What are the 3 membranopathies?
membranopathie → regenerative anemia (hemolysis)
- Spherocytosis → loss of vertical interactions
- Elliptocytosis → loss of horizontal interactions
- Defect inside the cytoskeleton → RBC is elongated - RBC hydration is maintained through ionic channels and pumps
- Intracellular Ca2+ (by activating GARDOS channel) is the main parameter of H2O flux regulation
- Overhydrated hereditary stomatocytosis
- Dehydrated hereditary stomatocytosis (xerocytosis)
*Can see all in the microscope with a blood smear
What causes paroxysmal nocturnal hemoglobinuria?
Somatic (acquired) variant (mutation) in PIGA gene (coding for GPI)
GPI is an anchor for CD55 and CD59 proteins that prevent complement activation
=> Acquired loss of CD55 and CD59 => Complement mediated hemolysis
*Encoded by PIGA locus on the X chromosome
Can be diagnosed by treating the samples in flow cytometry (CD55-CD59-)
What are clinical implications and treatment of paroxysmal nocturnal hemoglobinuria?
1) Acute hemolytic anemia Classically at night
2) Thrombosis
3) Bone marrow failure
Treatment:
Complement blocker (eculizumab)
Which enzymopathies cause regenerative anemia?
- G6PD deficiency
RBC are highly vulnerable to oxidative stress due to:
- High oxygen content
- Presence of only one defensive mechanism against free radicals: G6PD/NADPH pathway that produces reduced glutathione
*X-linked autosomal disease
- Pyruvate kinase deficiency
RBC do not have nucleus nor mitochondria, Energy supply rely on Glycolysis (Amount of pyruvate kinase already synthetized)
Without enough ATP, Na+ K+ ATPase pumps are the first to stop => Dehydration secondary to K+ leak
*Autosomal recessive disorder
What are the different classes of G6PD deficiencies?
Increased sensitivity to oxidative stress
- Class 2-3: Only while increased oxidative stress
(some drugs, ingestion of fava beans, infection) - Class 1: At baseline (permanent)
Hemolytic regenerative anemia
- Intermittent (class 2-3)
- Chronic (class 1)
What are 2 types of Autoimmune hemolytic anemia (AIHA)?
Autoimmune destruction of RBC, by:
- IgG → produced mainly in B-cells, most frequent
- Leads to macrophage phagocytosis → they remove small parts and end up with microspherocyte - IgM → bigger immunoglobulin, hemolysis in the liver and by complement activation
What are causes/test/features of Autoimmune hemolytic anemia (AIHA) by IgG?
Causes:
Primary (no underlying cause)
Secondary to
- Immunodeficiency
- Autoimmune disorder
- Leukemia/lymphoma
- Drugs
Direct antiglobin test (coombs test)
Agglutination at 37 degrees
=> Warm AIHA
- In a dish, put an Ab against IgG at the surface of RBC → will bind and agglutinate in the dish
- If no agglutination, it means the RBCs have no IgGs at their surface
Clinically classified as regenerative hemolytic anemia
What are features of Autoimmune hemolytic anemia (AIHA) by IgG?
Direct antiglobin test (coombs test) Agglutination at 3-4 degrees
=> Cold AIHA
Causes:
Primary
Secondary to
- Infection
- Lymphoma
What are clinical symptoms of Mechanic-caused Extracorpuscular Hemolytic Regenerative anemia?
And the dysfunction of organ implicated?
Mechanic
Clinically:
- Regenerative hemolytic anemia
- Thrombocytopenia (low blood platelet count)
- Schistocytes (fragmented red cells)
Dysfunction of the organ downstream of thrombi:
- Kidney (hemolytic and uremic syndrome)
- Brain (thrombotic thrombocytopenic purpura)
What are Infection-causes Extracorpuscular Hemolytic Regenerative anemia?
Malaria → RBC destruction
*regenerative hemolytic anemia
