Microcytic and macrocytic anemias Flashcards
What is the unifying pathogenic mechanism for all microcytic anemias?
Defect in RBC hemoglobin synthesis at a cellular level
What can a large RDW indicate?
In respect to microcytic anemia
The presence of a population of mixed normo/microcytic RBC population
Dimorphic RBC populations
Classically associated w/ sideroblastic anemia (myelodysplastic variant)
Microcytic RBCs arise from the mutated clone and normal rbcs from the unmutated one
Can also be seen in Pt’s w/ iron deficiency anemia who are treated w/ iron - normal cells representing those produced in response to iron supplementation, and microcytic RBCs arising from the period of iron deficient erythropoiesis
Pathway abnormailities in microcytic anemia
Defect in cellular heme synthesis
Defect in globin chain synthesis
Defect in heme synthesis in microcytic anemia
Unavailability of iron:
-iron deficiency; anemia of inflammation/chronic disease
-Defect in cellular heme/protoporpyrin synthesis
Defect in globin chain synthesis in microcytic anemia
-Thalassemias
-Thalassemia-like hemoglobinopathies: :
HbC
HbE (both β globin);
Hb Constant Spring(HbCS (α globin))2
Decreased serum iron
Increased Tf/TIBC w/ decreased Tf/Fe saturation%
Iron deficiency anemia
In early stages, MCV might be normal but is typically low
Microcytic RBCs in in iron deficiency anemia are typically also hypochromic (decreased MCHC, expanded area of central pallor)
Causes of iron malabsorption
- Celiac disease
- Autoimmune gastritis
- Bariatric surgery
- Achlorhydria (acidic pH required for optimal iron apsorption)
- Resection duodenum/proximal ileum
- Iron-refractory iron deficiency anemia (IRIDA) TMPRSS6 mutation; congenital microcytic/hypochromic anemia
Gene mutation associated w/ iron-refractory iron deficiency anemia (IRIDA)
TMPRSS6 mutation; congential microcytic/hypochromic anemia
Qualitative defects of globin synthesis
Hemoglobinopathies - characterized by the production of abnormal hemoglobin w/ an abnormal α or (more commonly) β globin chain resulting from a mutation in the globin gene
Quantitative defects of globin synthesis
Thalassemias - . As a result of a mutation in a globin gene promoter, either α or β globin chains are not produced or are produced at a decreased level that leads to imbalance between α and β globin production. It is this imbalance that causes the anemia
Thalassemia associated w/ increased levels of HbF and/or HbA2
β thalassemia syndromes
Asymptomatic Pt who is not anemic, has normal iron studies, but has MCV in the 70s
Almost certainly has a thalassemia syndrome (thalassemia trait)
HbA2 and/or HbF are elevated
β thalassemia
Target cells
Thalassemia patients other than silent carriers have “target cells” (they look like targets).
infrequent in αα/-α thalassemia, β+/β thalassemia, more common in other phenotypes.
Nucleated RBCs in thalassemia
Indicates extramedullary hematopoiesis
HbH stained w/ new methylene blue or brilliant cresy blue
HbH cannot be quantified w/ HPLC
Thalassemia that requires molecular testing
Since the most common α thalassemia syndromes do not produce an abnormal hemoglobin, the vast majority of α thalassemia patients will have normal hemoglobin quantitation. The diagnosis can be inferred by patient and family history, but requires molecular studies to confirm it. Molecular studies are almost never needed in β thalassemia
Thalassemia major
Transfusion dependent throughout life
Risk for Fe overload and complications like myocardial iron deposition-related heart disease and endocrinopathy (massive splenomagaly and extramedullary hematopoiesis)
Thalassemia minor
almost never require transfusion, are typically only mildly anemic;
many have mild splenomegaly but do not have the other complications above; and have a low risk of iron overload.
Thalassemia intermedia
Require transfusion sometimes.
They have some risk of developing the same complications as thalassemia major patients, and if they start developing those problems, they are put on chronic transfusion programs to prevent excess ERFE production and suppression of hepcidin.
Thalassemia trait
are usually not anemic at all or just barely; they have microcytosis but nothing else.
HbH disease
Clinical phenotype of thalassemia major/TDT
Frequently also have a small abount of Hb Barts (present w/ hydrops fetalis, severe TDT, and short survival)
They mostly show HbA becuase HbH is unstable
A β thalassemia syndrome with no HbA
β0 thalassemia
A β thalassemia syndrome with HbA
β+ thalassemia
α-/αα
α THALASSEMIA
clinically silent carrier
–/αα or α-/α-
α THALASSEMIA
(α thalassemia trait type 1 (cis))
or
α-/α- (α thalassemia trait type 2 (trans)):thalassemia trait
Type 2 trait most common in Black/African ancestry
type 1 trait most common in Asian, rare with Black/African ancestry
α-/–
ααND/–
αND-/α-
Hb H disease (Three absent or mutant genes; ND – non-deletion mutation, of which the best known is HbCS)
-TDT/thalassemia major; target cells; nucleated red cells
-Non-deletional mutations like αCS are associated w/ more severe phenotype
αND-/–
αND-/αND-
Hb Barts/hydrops fetalis (Four absent or mutant alleles total- two or three absent alleles with one or two mutant alleles)
-Severe TDT; short lived
β/β+ or rarely β/β0
o Mild anemia, microcytosis, some targets
o β thalassemia minor
o Strictly speaking there is no “β thalassemia trait” but some β/β+ behave like it
β/β0, or mild β0/β+
o Definite anemia, microcytosis, targets but typically no or rare transfusions
o β thalassemia intermedia
β0/β+, β0/β0
o Severe anemia, transfusion dependent, microcytosis, target cells, nucleated red cells
o β thalassemia major
Mechanism of anemia in thalassemias
Hemolysis due to cell damage from unbound globin chains
Patients with concurrent α thalassemia trait 2 (α-/α-) and β thalassemia minor are less anemic and microcytic than patients with beta thalassemia minor alone because they have less imbalance in α and β globin chain production.
Mechanism for iron overload
ERFE production/hepcidin suppression. Subsequent iron overload leads to osteoporosis and endocrinopathy
Extramedullary hematopoiesis
manifestation of extreme ineffective erythropoiesis causing
reactivation of embryonic blood production sites.
Luspatercept
activin receptor ligand trap that drives late stage erythropoiesis, is approved for use in thalassemia
Triad of saturnine gout
Patients with lead poisoning may have neuropathic abdominal pain, hypertension, joint pain, and kidney disease
Causes sideroblastic anemia
Macrocytosis/macrocytic anemia vs megaloblastic anemia
Macrocytic anemia - increased MCV, usually reflects presence of large RBCs (macrocytes)
Megaloblastic anemia - defects of nucleic acid synthesis results in specific morphologic changes in nucleated cells (particularly erythroid and myeloid precursors)
In megaloblastic anemia where are megaloblastic changes present?
Bone marrow - macrocyte you see in peripheral blood is not a megaloblast
What you do see in the peripheral blood in megaloblastic anemia:
(macroovalocytes) and neutrophils with a greater than usual number of nuclear lobes (hypersegmented neutrophils; usually 5 or more lobes)
What anemia typically reflects an abnormality in B12 or folate metabolism?
Megaloblastic anemia
Megaloblastoid changes
Congenital dyserythropoietic anemia (CDA)
Multinucleate erythroid precursors - hallmark of CDA
Do not have hypersegmented neutrophils in peripheral blood - do not have macroovalocytes
B12 and folate are normal
Diamond-Blackfan anemia
Macrocytic
Congenital form of pure red cell aplasia that is associated w/ mutation in the ribosomal regulatory proteins
Chronic liver disease:
the lipid composition of the RBC membrane is abnormal, causing “extra” membrane that produces a higher surface-tovolume ratio.
These cells have the appearance of target cells except that the target cells of thalassemia and hemoglobinopathies are microcytic.
These cells are large and the “target” is not precipitated globin but rather a fold of cell membrane.
Artifactual macrocytosis
MCV is measured as large but RBCs are normal size
- Rouleaux/RBC clumping
- RBC agglutination
Pt’s w/ rouleaux typically have eleved erythrocyte sedimentation rate and CRP (common labs to ID inflammation)
Cryoglobulinemia type I
Associated w/ hematologic malignancies
Cryoglobulinemia type II
Associated w/ hepatitis C
Cryoglobulinemia type III
Nonspecific indicator of inflammation (mixed cyroglobulinemia)
What enhances folate/THF retention in cells?
Polyglutamation
What biochemical conversion does methylene-THF acts as a one-carbon donor for?
The conversion of deoxyuridine monophosphate (dUMP) to thymidylate monophosphate
Enzyme for conversion = thymidylate synthase
Leads to release of dihydrofolate (reduced back to THF by dihydrofolate reductase)
Required for DNA synthesis
Methyl-THF
If methylene-THF is not metabolized by thymidylate synthase, it is irreversibly reduced by methylene-THF reductase (MTHFR) to methyl THF.
MethylTHF is not polyglutamated as effectively as other THF forms and tends to diffuse out of cells and be lost in the urine
Methyl-THF is convered to THF by methionine synthase (B12 dependent enzyme)
Elevated homocysteine levels
In respect to anemia
Macrocytic anemia caused by either B12 or folate deficiency
Methylmalonic acid accumulation
Accumulates in B12 deficiency only
Haptocorrin
R-protein/factor
Glycoprotein produced in salivary glands - binds cobalamin in the stomach
Pancreatic proteases in the presence of bicarb digest haptocorrin - releases the cobalamin
Cobalamin then becomes bound to IF
Intrinsic factor
Produced by parietal cells in stomach
After haptocorrin-cobalamin complex is degraded in duodenum, cobalamin binds IF
IF-cobalamin complexes then travel to ileum where they bind with the cubam receptor - internalized in lysosomes
What exports IF-cobalamin complex from lysosomes?
2 receptors:
LMBD1 and ABCD4
After exportation from the lysosome, what exports cobalamin B12 into circulation?
Transcobalamin
What mediates cellular uptake of B12?
The transcobalamin receptor = CD320
Deficiency of transcobalamin vs deficiency of haptocorrin?
TC deficiency - megaloblastic abnormality
HC deficiency - does not produce disease
What are Pt’s w/ congenital hemolytic anemias and severe exfoliative skin diseases (i.e. psoriasis) at risk for?
Folate deficiency
What drugs can induce actual or functional B12 deficiency?
NO
Metformin
Histamine-blocking agents or PPis
Imerslund-Grasbeck syndrome
Defective cubam receptor leading to B12 deficiency
Most common cause of B12 deficiency?
Pernicious anemia - caused primarily by Abs against IF, and secondarily by autoimmune gastric atrophy leading to loss of parietal cells
Drugs that interfere w/ folate activity
Antifolates: carbamazepine, methotrexate, premetrexed, phenytoin, sulfasalazine, trimethoprim, valproic acid
Drugs that require methylation: L-Dopa, α-lipoic acid, high dose niacin
Inborn defects of folate metabolism that causes megaloblastic anemia
Methylene-THF DH deficiency (MTHFD1)
MTHFR deficiency does not cuase megaloblastic anemia
Causes of megaloblastic anemia not due to B12/folate deficiency
Antineoplastic/immunomodulatory: Azathiprine, 5-fluorouracil, hydroxyurea, 6-mercaptopurine, mycophenolate mofetil
Tyr kinase inhibitors: imantinib, sunitinib
Antitetrovirals: zidovudine, stavudine
Infancy-onset of megaloblastic anemia, sensorineural deafness, diabetes, optic atrophy. High dose thiamine corrects anemia
Thiamine responsive megaloblastic anemia
Autosomal recessive
SLC19A2 family gene for high affinity thiamine receptor
Hereditary orotic
aciduria
Developmental delay with or without megaloblastic anemia. Responds to uridine
Autosomal recessive
Uridine monophosphate synthase
gene → impaired pyrimidine
synthesis
Lesch-Nyhan
syndrome
Abnormal uric acid metabolism, severe neurobehavioral issues, and megaloblastic anemia
X-linked
Hypoxanthine-guanine phosphoribosyltransferase (HGPRT)
mutation → impaired purine metabolism
MCV greater than 115 fL
Increases the likelihood that macrocytic anemia is due to B12
Although MCVs that high or
higher are routine in patients taking
hydroxyurea
Serum B12 assay
Measures both transcobalamin and haptocorrin
Normally - ~80% HC-B12 and ~20% TC-B12
Elevated serum B12
primarily reflects elevated unbound (apo) HC, and less frequently elevated apo-TC. This occurs most commonly in liver disease but can be seen in myeloproliferative disorders (it was once considered a minor criterion for the diagnosis of polycythemia vera).
Elevated B12 levels do not carry an adverse implication in and of themselves.
Elevated LDH and bilirubin
In context of megaloblastic anemia
Serum lactate dehydrogenase (LDH) and bilirubin may be mildly elevated, reflecting intramedullary hemolysis from ineffective erythropoiesis. Serum/plasma haptoglobin may low.
Subacute combined degeneration in the posterior/lateral columns of the spinal cord
Reflects demyelination in B12 deficiency
MRI = hyperintense lesion in the posterior part of the cervical spinal cord (V sign)
Anti-IF Abs imply
Pernicious anemia
Anti-parietal cell Abs imply
Atrophic gastritis
Esophagogastroduodenoscopy tests for?
Achlorhydria/gastric atrophy
Anti-endomysial IgA implies
Celiac disease
Elevated serum gastrin implies
Achlorhydria/gastric atrophy
Low serum pepsinogen implies
Immune or atrophic loss of parietal cells
Mutation associated w/ HbE syndrome
β26 Gln(Q) → Lys (K)
Two persons who each have alpha thalassemia trait type 2 (trans; α -/α -) are planning to have a child together. What is the likelihood that the child will have HbH disease?
0%
What is the pathenogenic mechanism for X-linked sideroblastic anemia?
Impaired heme/protoporphyrin synthesis (defective 5-ALA synthase)
Hypochromia
Increased central pallor of RBCs
In a woman with a hematocrit of 40% (normal 36-48%), the reticulocyte production index (RPI) will be (greater than; lower than; or the same as;) the corrected reticulocyte count?
Same as
Isoniazid-associated sideroblastic anemia can be prevented by?
Pridoxine (B6) supplementation
Which of the following contributes to iron overload in Pt’s w/ congenital X-linked sideroblastic anemia?
A. Increased erythroferrone production
B. Increased 5-ALA synthase activitiy
C. Increased pyridoxal-6-phosphate metabolism
D. Increased hepcidin production
A. Increased erythroferrone production
Reticulocyte index
Frontal bossing
Typical characteristic of thalassemias
Due to infeffective heamtopoeisis
Pathogenic mechanism of Hb constant spring (CS)
α142 STOP → Gln(Q)
(gives a long unstable α chain)
Pathogenic mechansim of HbC syndrome
β6 Gln(Q) → Lys (K)
B. Hemoglobin concentration
RBC# and red cell size (MCV) and hemoglobin concentration are only values that are measured directly
C. 36%
D. Polychromatophilic cytoplasm
Restless legs syndrome
PICA - is the most specific sx
C. Decreased cellular Hb synthesis
C. Low serum ferritin
MCV<75fL
Almost always hemoglobinopathy or thalassemia
D. 0%
HbE syndrome
Hb constant spring syndrome
C. SF3B1 mutation
Tx w/ rhEPO; transfusion/chelation; Luspatercept
Why is oral B12 replacement in pernicious anemia effective?
B12 is absorbed by intrinsic factor-independent processes
How does high-dose niacin induce functional folate deficiency?
By depleting methyl groups required for folate effects
How does infection w/ Giardia lamblia cause B12 deficiency?
Competition for intestinal cobalamins
Diphyllobothrium latum is another pathogen that competes with cobalamins
The initial step in the metabolism of dietary folate naturally occurring in food is?
Hydrolysis by folypolyglutamate hydroxylase
Where is haptocorrin (cobalaphilin) produced?
Salivary glands
Which of the following participates in the reaction converting homocysteine to methionine?
A. Thymidylate monophosphate
B. Methelene-THF
C. Methylmalonyl CoA
D. Methyl-THF
D. Methyl-THF
The peripheral blood smear of a patient with B12 deficiency anemia would be expected to contain which of the following?
A. Megaloblasts
B. Macroovalocytes
C. Giant metamyelocytes
D. Multinucleated erythroblasts
B. Macroovalocytes
RBC agglutination is characteristic of which of the following disorders?
A. Multiple myeloma
B. Mixed cryoglobulinemia
C. Acute inflammatory arthritis
D. B12 deficiency
B. Mixed cryoglobulinemia
D. Copper deficiency
Non-megaloblastic, macrocytic anemia causes
Common cause of copper deficiency induced macrocytic anemia
Zinc toxicity - copper and zinc compete for absorption
A. Hepatitis C (cryoglobulinemia type II)
B. Cubulin/amnion-less
Cubam, a multi-ligand receptor that absorbs vitamin B12 and reabsorbs proteins in the kidney, is made up of two proteins: cubilin and amnionless:
Cubilin: A cell receptor that recognizes the vitamin B12-intrinsic factor complex
Amnionless: A transmembrane protein that anchors the receptor to the membrane and helps with endocytosis
B. Binding to protein-coupled folate transporter
Dietary folic acid is polyglutamated and needs to be hydrolyzed by folypolyglutamate hydroxylase before binding to protein-coupled transporter
C. Both B12 and folate absorption (although folate is absorbed more broadly it will be impacted)
B. Hemodialysis
All answer choices are associated w/ folate deficiency - only hemodialysis is associated w/ loss (B12 does not dialyze)
Non-drug-related causes of folate deficiency
Methylene-THF DH (MTHFD1) - inborn defect of folate metabolism
Also; pregnancy, hemolytic anemia, exfoliative skin disease, leukemia, and hemodialysis
C. Thiamine-responsive megaloblastic anemia
Due to defect in SLC19A2 family gene (high-affinity thiamine recetor)
C. Serum anti-intrinsic factor antibodies
Serum methylmalonic acid accumulation just indicates B12 deficiency
Common causes of secondary B12 deficiency
Obesity (common)
HIV (fairly common)
B12 deficiency effect on RBC folate content
B12 deficiency inhibits methionine synthase, which leads to accumulation of methyl-THF (able to diffuse out of RBC) leading to low RBC folate levels
D. Terminal ileum resection
“pernicious anemia is second best answer”
