Hematopathology Flashcards
RBC Life Cycle/ Structure
- EPO → normoblasts → loss of nucleus → reticulocytes → mature RBC
- Reticulocyte stage: 5-7 days
- RBC life span: 120 days
RBC Parameters (4)
• Mean Cell Volume (MCV): average volume of an RBC • Mean Cell Hemoglobin (MCH): average content of Hb per RBC • Mean Cell Hemoglobin Concentration (MCHC): average concentration of Hb in a given volume of RBC’s • Red Cell Distribution Width (RDW): coefficient of variation of RBC volume
Hemolytic Anemias
ETIOLOGY:
- Intravascular Hemolysis: mechanical injury to RBC
- Defective cardiac valves
- Microvascular thrombi
- Complement Fixation
- Infections (malaria, clostridia toxin)
- Extravascular Hemolysis: RBC rendered deformed or foreign
- Spherocytosis
- Sickle Cell anemia
- Immune antibody coating
PATHOGENESIS: shortened RBC life span - increased erythropoietin and erythropoiesis
- Intrinsic RBC Defect: membrane defect (spherocytosis), enzyme defect (G6PD), hemoglobin defect( Sickle cell and Thalassemias)
- Extrinsic RBC Defect: Immune mediated damage, trauma, infections Acute Hemorrhage - hypovolemia chronic Hemorrhage - iron stored becomes depleted
MORPHOLOGY:
- normochromic, normocytic anemia
- Polychromasia
- Erythroid hyperplasia
- Increased bilirubin, hemoglobin, and LDH
- Decreased Haptoglobin
Hereditary Spherocytosis
ETIOLOGY: mutated proteins in the RBC membrane skeleton
- Northern Europeans
- Autosomal dominant
MORPHOLOGY: RBCs become spheroid and rigid
• With splenectomy → Howell-Jolly Bodies (DNA remains left due to splenectomies)
PATHOGENESIS: reduced RBC membrane stability → 10-20 day life span
- Ankyrin
- Band 3
- Spectrin
- Band 4.2
- Reduced RBC membrane stability → loss of small fragments during normal shearing stresses in the blood circulation → RBCs become increasingly more spherical → unable to traverse the splenic sinusoids → phagocytosis and destruction by splenic macrophages (spleen usually enlarged)
SYMPTOMS: chronic hemolytic anemia, gall stones (increased bilirubin)
- TREATMENT: splenectomy → anemia corrects, spherocytosis persists
- DIAGNOSIS:
- Osmotic Fragility Test: when exposed to hypotonic salt solutions → RBCs lyse prematurely
- Increased MCHC (only one)
- Increased LDH
G6PD Deficiency
- ETIOLOGY: abnormality in the Hexose Monophosphate Shunt due to impaired enzyme function - leaves RBC’s prone to oxidative injury
- X-linked recessive
- G6PD Type B = most common
- African Americans (Type A)
- Mediterranean/Middle Eastern (Type B)
- PATHOGENESIS: exposure to oxidants (abnormal protein folding and increased proteolytic degradation) → oxidation of SH groups on globin chains → precipitation of denatured globins = Heinz bodies
- severe damage → RBC to spleen → macrophage bite out inclusions → bite cells → extravascular hemolysis
- Presentation follows infection, Sulfa drugs, fava beans
- SYMPTOMS:
- Acute hemolysis
- Neonatal jaundice (uncommon)
- Heterozygote advantage against P. falciparum malaria
Sickle Cell Disease (HbS)
- ETIOLOGY: point mutation at position 6 in B-globin chain (glutamic acid → valine)
- 10% of African Americans are HbAS (heterozygotes)
PATHOGENESIS: HbS aggregate during crises (sticky) - formation of long-needle like structures
SICKLING FACTORS:
- Amount of HbS & its interaction with other Hb chains in the red cell:
- HbA & HbF decrease sickling; HbC sickling increased. - Hb concentration per red cell: Dehydration increased sickling Coexisting α-thalassemia decreases sickling (less globin, therefore less hemoglobin). - Acidity: lower pH increases sickling. -Length of exposure to low O2 tension.
CRISIS
- Vaso-occlusive/ painful crises: ischemic events due to microvascular occlusions
- Sequestration crises: rapid pooling of blood in the spleen.
- Aplastic crises: acute viral infection, due to parvovirus B19 (infects red cell precursors).
- Hemolytic crises.
MORPHOLOGY: target cells
SYMPTOMS:
- Chronic hemolysis (intravascular & extravascular)
- Hyperplastic bone marrow → skull bone changes in kids
- Repeated infarction and fibrosis → Autosplenectomy in children → susceptible to H. influenzae and Pneumococcus
- Jaundice
- Microvascular occlusions
- Osteomyelitis with Salmonella infections
- Aplastic crises: acute viral infection (Parvo B19)
DIAGNOSIS: mixing blood with O2 consuming agent induces sickling
• Hemoglobin electrophoresis
TREATMENT: analgesics, B9, Hydroxyurea (increases HbF)
B-Thalassemias
- ETIOLOGY: diminished synthesis of structurally normal B-globin chains (chromosome 11), with unimpaired alpha-chain production
- B+ Thalassemia: reduced B chains produced (mutation in promoter)
- B(o) Thalassemia: no B chains (mutation in splicing or chain termination) •
PATHOGENESIS: reduced survival of RBCs due to cell membrane damage by precipitated alpha-chains → ineffective erythropoiesis
- 75% of RBC precursors die in bone marrow
- Excessive iron absorption
- MORPHOLOGY: hypochromic, microcytic anemia
- Target cells
- TREATMENT: bone marrow transplants
B-Thalassemia Major Syndrome
- ETIOLOGY: presents 6-9 months after birth when HbF levels naturally fall
- Mediterranean, Africa, SE Asia
- PATHOGENESIS: B+/B+, B+/B(o), B(o)/B(o) = severe transfusion-dependent anemia
SYMPTOMS: • Expansion of hematopoietic marrow → prominent facial bones, erosion of bony cortex, new bone formation
- Hepatosplenomegaly → due to extravascular hemolysis
- Hemosiderosis
- Secondary hemochromatosis due to iron overload → cardiac failure, liver failure, pancreatic damage - growth retardation + death → unless given blood transfusion
DIAGNOSIS: • Hb levels = 3-6 g/dL
• HbF remains elevated
TREATMENT: iron chelator to prevent iron overload
B-Thalassemia Minor
• PATHOGENESIS: B+/B or B(o)/B = mild hypochromic, microcytic anemia
SYMPTOMS: usually asymptomatic
• DIAGNOSIS: hemoglobin electrophoresis: increased HbA2 with normal or elevated HbF
TREATMENT: avoid treating as iron-deficiency anemia
A-Thalassemia
- Silent Carrier: one alpha-gene deleted
- A-Thalassemia Trait: 2 genes deleted
- a/a, -/- (SE Asian)
- a/-, a/- (African)
- Hemoglobin H Disease: 3 genes deleted
- HbH is formed from tetramers of excess B-chains → high affinity for O2 → hypoxia
- HbH oxidation →precipitated inclusions in RBCs → spleen → extravascular hemolysis
- Hydrops Fetalis: all 4 genes deleted (incompatible with life)
- Hb Barts formed from tetramers of excess gamma-chains → high affinity for O2 → no O2 reaches the tissues → death unless given intrauterine transfusion
Paroxysmal Nocturnal Hemoglobinuria (PNH)
- ETIOLOGY: rare acquired clonal stem cell disorder associated with periodic hemolysis
- X-linked
- Phosphatidylinositol glycan class A (PIGA)
PATHOGENESIS: PIGA gene synthesizesglycosylphosphatidyl inositol (GPI)
- GPI (anchors CD55/CD59) inhibits complement activation on blood cells
- At night → hypoventilation → decreased pH → complement activated
- PNH is rare → PIGA clones gain selective advantage to produce disease
SYMPTOMS: intravascular hemolysis, pro-thrombotic state (40% develop venous thrombosis)
- Hemoglobinuria, hemosiderinuria
- Iron deficiency
- Aplastic anemia
- 5-10% develop AML or Myelodysplastic Syndrome
DIAGNOSIS:
- Sucrose hemolysis test (screening)
- Ham’s Acid hemolysis test
- Flow Cytometry: absence of CD55 and CD59 on WBC’s
- Flaer Test
TREATMENT: Immunosuppression
Warm Antibody Immunohemolytic Anemia
- ETIOLOGY: most common form of IHA
- 50% are idiopathic
- 50% have predisposing autoimmune disease, lymphoma or drug reactions • Most antibodies are IgG
Cold Antibody Immunohemolytic Anemia
- ETIOLOGY: IgM antibodies bind and agglutinate RBCs at <4C SYMPTOMS: • Acute Self-limiting Hemolysis: seen in infectious diseases (CMV, HIV, Influenza, Mycoplasma pneumonia)
- Chronic Hemolysis: idiopathic or associated with lymphoma
Direct Antiglobulin Test (DAT):
Detection of antibodies ± complement on patient RBCs. Patient RBCs are incubated with antibodies to these elements → RBC agglutination - anti- antibodies → bind to patient RBC’s
Indirect Antiglobulin Test (IDAT):
- Patient serum is tested for its ability to agglutinate test RBCs that have known antibodies bound onto them. -Temperature dependence defines “warm” or “cold”.
Megaloblastic Anemias
- ETIOLOGY: deficiency of Vitamin B12 (cobalamine) or B9 (folate)
- Poor people, pregnant women, alcoholics, overcooked food, impaired absorption
PATHOGENESIS: both vitamins are coenzymes required for synthesis of thymidine (methionine synthase, thymidylate synthase)
- B9 → Impaired DNA synthesis → ineffective erythropoiesis → destruction of macrocytes
- B12 → Autoantibodies → Blocked IF (parietal cells) → B12 def. → Megaloblastic anemia
- MMA requires cobalamin. B12 deficiency increases urine methyl malonic acid -Neurological deficits → dorsal and lateral tracts affected: sensory and functional functions affected
- MORPHOLOGY: pancytopenia with macrocytic anemia
- (MCV>100)
- Decreased reticulocyte count
- Enlarged hyper-segmented neutrophils (5+ lobes)
- Hypercellular bone marrow
- Increased homocysteine
SYMPTOMS: Fatigue, atrophic glossitis, cheoilsosis
• Neurological symptoms → B12 ONLY → Decreased vibration/proprioception, degeneration of dorsal/lateral tracts of CNS
Pernicious Anemia
• Type II Hypersensitivity
ETIOLOGY:
- Decreased intake (diet deficient → strict vegetarian)
- Impaired GI absorption → pernicious anemia, malabsorption (IF defect)
- Common in N. Europeans, ages 40-80
PATHOGENESIS: autoimmune atrophic gastritis → failure of IF production → B12 not absorbed → B12 deficiency → Megaloblastic anemia
- SYMPTOMS: CNS deficits → sensory ataxia, lower limb parasthesia
- Atrophic gastritis
- DIAGNOSIS:
- Increased plasma and urine methyl-malonic acid
- Increased serum homocysteine
- Increased MCV
- Decreased reticulocytes
- Schilling Test: inability to absorb oral B12
- Reticulocyte Response: improvement of anemia 5 days after paraenteral B12 injections
- serum antibodies to intrinsic factor
Folate Deficiency
- ETIOLOGY:
- Decreased intake: inadequate intake of green vegetables (alcoholics)
- Impaired GI absorption
- Increased requirements (pregnancy, infancy, cancer therapy)
SYMPTOMS: no CNS symptoms DIAGNOSIS:
- Increased homocysteine
- Decreased serum folate (differentiation b/w B12 deficiency)
Iron Deficiency Anemia
• Microcytic hypochromic anemia
ETIOLOGY: most common cause of anemia worldwide
- Dietary deficiency
- Impaired absorption ( normally absorbed in the duodenum)
- Increased requirements: growing infants, premenopausal female, pregnancy
- Chronic blood loss (most commonly due to chronic GI blood loss)
DIAGNOSIS:
- CBC: decreased Hb, decreased MCV, increased RDW
- Blood Smear: hypochromic microcytic anemia, sometimes poikilocytosis (pencil cells)
- Biochemical: decreased transferrin saturation, increased TIBC, decreased ferritin
- Depletion of BM iron stores: Prussian Blue stain of bone marrow is negative
NORMAL METABOLISM: mostly absorbed in the duodenum
- Hepcidin: inhibits ion uptake from duodenal mucosal cells in response to high levels of iron stores
- Free iron is toxic → Fe is bound as ferritin
- Storage: ferritin (in liver, spleen, BM, muscle) + hemosiderin
- Transport: transferrin
- Functional iron → 80% is bound to hemoglobin
SYMPTOMS: Koilonychia, decreased reticulocytes, MCV, MCHC
- Plummer Vinson Syndrome = Iron deficiency anemia, proximal esophageal webs, atrophic glossitis
- Pica Syndrome = Eat dirt, ice (psychiatric problems)
Anemia of Chronic Disease
- ETIOLOGY:
- Chronic bacterial infections: lung abscesses, endocarditis, tuberculosis
- Chronic immune disorders: rheumatoid arthritis
- Malignant tumors: lung, breast, lymphoma
PATHOGENESIS: impaired iron utilization and decreased RBC production
- Increased Hepcidin → decreased transfer of iron from bone marrow pool to RBC precursors due to inflammatory mediators
- Decreased erythropoiesis with low EPO
- MORPHOLOGY: hypochromic, microcytic anemia
DIAGNOSIS: decreased serum Fe, decreased TIBC (transferritin) , increased ferritin
