Hematology Flashcards
How do sites of hematopoiesis differ between infants and adults?
Infants: marrow in all bones
Adult: more limited: vertebrae and pelvis, ribs, sternum, skull, sacrum, proximal ends of femur
What are the sites of fetal hematopoiesis?
0-2 mos: yolk sac
2-7 mos: liver and spleen
5-9 mos: bone marrow
In bone marrow, how many cells are stem cells?
1 in 20x10^6 (20 million)
Beyond this: sign of potential leukemia
What are molecular markers for hematopoietic stem cells (HSCs)?
HSC: CD34+ and CD38-
Once committed to differentiation, become CD38+, but lack lineage specific markers.
What transcription factors regulate the survival of HSCs in bone marrow?
NOTCH-1
GATA-2
What transcription factors commit cells to the myeloid lineage in early hematopoiesis?
PU.1
CEPB family
What transcription factors commit cells to erythropoietic and megakaryopoietic lineages?
GATA-1
FOG-1
Where are Erythropoietin and Thrombopoietin produced?
EPO: 90% in kidney
Thrombopoietin: Liver
3 roles of growth factors in hematopoiesis
- control of cell cycle
- gene activation
- inhibition of apoptosis
What is BCL-2?
Anti-apoptotic protein
Production stimulated by growth factor
Inhibits release of cytochrome C from mitochondria
3 families of adhesion molecules
Immunoglobin superfamily: antigen dependent surface receptors (TCR, etc) and antigen independent surface adhesion molecules
Selectins: leukocyte and platelet adhesion to endothelium
Integrins: cell adhesion to ECM
What is CFU-GEMM?
first step of erythropoiesis: commitment of pluripotent stem cells to non-lymphoid lineage
CFU-GEMM: Colony Forming Unit - Granulocyte, Erythrocyte, Megakaryocyte, Macrophage
What is BFU-E?
Erythrocyte Burst Forming Unit - first committed erythroid progenitor
divides -> CFU-E
Is there RNA in the cytoplasm of an RBC?
No
What is erythropoietin? Where is it produced?
Glycosylated polypeptide (165 AA) 90% produced by peritubular interstitial cells of kidney 10% in liver and elsewhere
What factors in the kidney stimulate erythropoietin production?
HIF-2a and B
hypoxia induced
What type of anemia results following kidney damage (failure, removal, etc.)
Normochromic, normocytic
Because of reduced production rather than Hb or structure problem.
What is normal adult hemoglobin and what are its subunits?
HbA
consists of 2a and 2B
What forms of Hb are normally found in adult blood?
HbA (a2B2): dominant
HbF (a2Y2): fetal
HbA2 (a2d2):
Where are the components of hemoglobin synthesized?
All in RBC precursor cells
protoporphyrin: in mitochondria
Fe2+: transported by Transferrin -> mito -> + protoporphyrin -> haem
Globin: ribosomes
What is the P50 of hemoglobin under normal conditions? How does it change?
P50: partial pressure of O2 at which Hb is 50% sat.
normal blood: 26.6
increased affinity: falls
decreased affinity (ex. 2,3-DPG): rises
4 factors that move Hb O2 dissociation curve to the right
Move to right (low O2 affinity) high 2,3-DPG high H+ high CO2 HbS
factors that move Hb O2 dissociation curve to the left
Move to left (high affinity)
low 2,3-DPG
low H+
HbF
What is methemoglobinemia? Causes?
Circulating Hb w/ Fe3+ rather than 2+ (patients often cyanotic)
Hereditary HbM: AA substitution affecting heme pocket
Hereditary deficiency of methemoglobin reductase
Toxic: drug or toxin induced oxidation of Fe2+ in Hb.
How do RBCs produce energy?
ATP and NADH: Embden-Meyerhof pathway (glycolytic)
NADPH: Hexose Monophosphate Shunt (PPP)
Important proteins in RBC membrane structure.
Band 3 (Cl- / HCO3- exchanger): binds ankyrin which binds protein 4.2 which together bind alpha spectrin
Glycophorin binds protein 4.1 and actin which bind spectrin
What is the relationship between anemia and 2,3-DPG?
2,3-DPG usually rises in setting of anemia -> rightward shift of Hb / O2 dissociation curve: Hb gives O2 to tissues more readily.
With what Hb concentration do symptoms of anemia usually become apparent?
9-10 g/dL
What are the criteria for microcytic, hypochromic anemia, and what are the causes?
MCV: <27pg
Iron deficiency, thalassemia, anemia of chronic disease (some), lead poisoning, sideroblastic anemia
What constitutes normocytic, normochromic anemia and what are the types / causes?
MCV: 80-95 fL
MCH: >27pg
may be hemolytic or non-hemolytic
Acute blood loss, chronic disease, renal disease, mixed deficiencies, bone marrow failure (post-chemo)
What constitutes macrocytic anemia and what are the causes?
MCV >95 fL
Megaloblastic: B12 or folate deficiency
Non-megaloblastic: ETOH, liver disease, myelodysplasia, aplastic anemia
What is a normal reticulocyte count (% and absolute) and how does it change with anemia?
Normal: 0.5-2.5%, absolute: 50-150x10^9 /L
should rise w/ anemia due to increase EPO
If anemia is suspected, what should the first step be toward making a diagnosis?
look at a blood film to count / characterize
What stain is used to visualize RNA and Heinz bodies in a blood smear?
Methylene Blue (supra-vital staining)
What are Pappenheimer bodies?
Iron containing RBC/reticulocyte inclusions - siderotic granules
What is a Howell-Jolly body?
DNA remnant seen in reticulocytes
What are Heinz bodies?
Reticulocyte/RBC inclusions of oxidized, denatured Hb
What is ineffective hemopoiesis?
Death of erythroblasts before production of mature cells
Normally, 10-15% of developing erythroblasts die in marrow.
What is seen in anemia w/ ineffective hemopoiesis?
If marked: elevated unconjugated bilirubin and lactate dehydrogenase
Low reticulocyte count relative to degree of anemia and number of erythroblasts in marrow.
How is total erythropoiesis assessed?
Marrow cellularity
myeloid : erythroid ratio (normally 2.5 : 1 to 12 : 1, smaller with increased erythropoiesis)
What are microscopic features of Iron deficiency anemia?
Central pallor in RBCs (>1/3 diameter)
Small RBCs (smaller than lymphocyte)
“pencil” cells
4 causes of iron deficiency anemia
- dietary lack
- impaired absorption
- increased requirement
- chronic blood loss (most importantly)
What is the gold standard test for iron deficiency anemia?
Prussian Blue staining of Bone Marrow
Reveals a lack of granular iron stores
Where in the GI tract is iron absorbed?
Duodenum (mostly proximal)
3 ways iron is absorbed in duodenum
1) complexed with mucin
2) complexed with ascorbate
3) complexed with heme (globin enzymatically removed)
How is iron transported from intestinal enterocytes into plasma?
Fe2+ is transported across basolateral membrane by ferroportin, oxidized to Fe3+ by hephaestin and released into plasma where it binds Transferrin
What is hephaestin?
ferricoxicase enzyme in basolateral enterocyte membrane. Oxidizes iron to Fe3+
How is iron transported into enterocytes?
Fe3+ -> Fe2+ in lumen by dcytb on brush border (ferric reductase)
Transported across by DMT-1
What is dcytb?
Ferric reductase found on apical brush border of duodenal enterocytes.
Fe3+ -> Fe2+ for transport into cell by DMT-1
What is DMT-1?
transporter on apical brush border of enterocytes. Transports Fe2+ into cell
How is iron transported in the blood?
Solubilized by Transferrin, which carries 80% to bone marrow and most of the rest to liver and kidney
Where is Transferrin produced?
liver
What is ferritin?
Iron storage protein found in many cell types
Hepatic parenchymal cells, macrophages
What is ferrochelatase?
heme synthetase
found in mitochondria. inserts iron into protoporphyrin
How much of absorbed iron is incorporated into Hb?
80%
rest in storage
What are and how do IRE and IRPs work?
IRE: iron responsive element - found in iron metabolism mRNA
IRP: iron responsive protein - IRE affinity modulated by iron levels
In high iron levels: IRP binds iron and has low affinity for IRE
Iron deficiency: IRP affinity for IRE is enhanced:
IRP binding in 3’ region ->up-regulation of transferrin receptor
and DMT-1
IRP binding in 5’ region -> down-regulation of ferritin and ALA
synthetase
What is the function of hepcidin?
Central regulator of iron metabolism
High levels of hepatic iron uptake -> Hepcidin production
Hepcidin binds ferroportin -> internalization and degradation -> DECREASED IRON ABSORPTION
What is TfR2?
Hepatic trasnferrin receptor - hepatocellular iron uptake.
What is the effect of inflammation on iron metabolsim?
Inflammation -> cytokine production, esp IL-6 -> increased hepcidin -> decreased iron absorption; increased hemophagocytosis, decreased erythropoietin production -> inhibited erythroid proliferation
What is ceruloplasmin?
ferricoxidase enzyme in plasma, oxidezes iron (Fe2+ -> Fe3+)
How much iron is in 1g of Hb?
3.5 mg
How much iron is absorbed / lost daily?
1-2 mg absorbed
1-2 mg lost (desquamation, sweat, no pathway)
How much iron is lost in a pregnancy?
500 mg total
How much iron is lost in a menstrual period?
4-100 mg
Physical signs of iron deficiency
Glossitis
Angular chelosis
Concave nails
What is TIBC?
Total Iron Binding Capacity
What happens to TIBC in Iron Deficiency Anemia?
Increased due to increased hepatic production of Transferrin
What lab tests are ordered in iron deficiency anemia and what are the usual findings?
Serum Transferrin: elevated
Serum Iron: low
Serum Ferritin: low
What is the preferred oral iron suppliment?
Ferrous Sulfate 324 mg (65mg iron) 3x daily
Is dietary intervention appropriate for iron deficiency anemia?
No - 3oz steak contains 3mg iron
adults need 150-200 mg = 10lbs steak
What are benefits of IV iron therapy?
Correction of nonhematologic effects of iron deficiency
Enhanced erythropoiesis
What is the #1 reason for failure to respond to oral iron supplimentation?
Failure to take pill
What is hereditary hemochromatosis and what kind of anemia does it produce?
#1 single gene inherited disease in US Not anemic - iron overload Iron deposits in organs -> dysfunction
What is the most common mutation found in heredetary hemochromatosis?
C282Y in HFE gene (6p21.3)
Mutation results in low levels of hepcidin -> elevated levels of ferroportin and increased iron absorption
How is iron toxic (as in hemochromatosis)?
Direct tissue toxicity
- lipid peroxidation via iron-catalyzed free radical rxns
- stimulation of collagen formation by stimulation of hepatic stellate cells
- interaction of reactive oxygen species and of iron itself w/ DNA
How many blood transfusions does it take for signs of iron overload to become apparent?
10-20 transfusions
200mg iron / unit blood
How is iron overload (hemochromatosis) treated?
phlebotomy goals: ferritin <50
Conditions associated w/ anemia of chronic disease
Rheumatoid Arthritis
Chronic infections (osteomyelitis)
Inflammatory Bowel Disease
Cancer
What is the primary mechanism underlying anemia of chronic disease?
IL-6 produces an increase in hepcidin -> decreased iron absorption, decreased iron release from macrophages Erythropoietin depression (production in kidney and decreased sensitivity in bone marrow)
Features of anemia of chronic disease
Low serum iron Low serum transferrin Low transferrin saturation Decreased TIBC Normal to High serum ferritin
What defines a finding of hypersegmented PMNs?
> 5% PMNs w/ 5 nuclear lobes or more
What causes megaloblastic anemia?
Vitamin B12 or folate deficiency or metabolic impairment-> impairment of DNA synthesis (impaired thymidine and purine synth)
What are some causes of non-megaloblastic macrocytic anemia?
Liver disease, hemolysis, splenectomy, Myelodysplastic syndromes, hypothyroid, hemorrhage, etoh, pregnancy
What abnormal RBCs are seen in non-megaloblastic anemia assoc. w/ liver disease?
target cells, stomatocytes
What is a schistocyte?
Fragmented RBC - seen in hemolysis that may be associated with macrocytosis
Are patients who have undergone splenectomy typically anemic?
No, though they may display macrocytosis with Howell-Jolley bodies
What are Pelger-Huet cells?
bilobed PMNs seen in myelodysplastic syndrome
What is the association between hypothyroidism and macrocytosis?
May be due to nutrient malabsorption or menorrhagia
What is a normal serum B12 level
> 400 pg/mL
What are 2 important biochemical roles of vitamin B12?
serves as a cofactor
1: Methylcobalamin: cofactor for methinonine synthase (methyltransferase): Homocysteine + mTHF -> methionine + THF
2: Adenosylcobalamin: cofactor for methylmalonyl CoA mutase: Methylmalonyl CoA -> Succinyl CoA
B12 deficiency results in the elevated levels of what substances?
Precursors in reactions in which B12 is a cofactor:
homocysteine and methylmalonyl CoA
How is B12 absorbed?
in food -> stomach where R-protein binds -> duodenum -> pancreatic enzymes degrade R-protein -> IF binds -> enterocyte -> IF degradation -> transcobalamin II binding and absorption to blood
What antibodies are associated with pernicious anemia?
Intrinsic Factor Autoantibodies (IFA): 100% specific for atrophic body gastritis
Gastric Parietal Cell Autoantibodies (PCA): non-specific for atrophic body gastritis
What are gastric parietal cell autoantibodies associated with?
autoimmune gastritis
What does a positive IFA titer indicate?
IFA: Intrinsic Factor Autoantibody
Indicates atrophic damage in gastric body mucosa (contributes to pernicious anemia)
Where is folic acid absorbed?
proximal jejunum
What is the daily intake requirement for B12 and folate?
B12: 7-30 mcg
Folate: 50-100 mcg
What are body stores of B12 and Folate?
B12: 2-3 mg (enough for 2-4 years)
Folate: 10-12 mg (enough for 4 months)
How is folic acid lost from the body?
bile and urine
What is methotrexate’s role in folate deficiency?
inhibits folic acid -> THF rxn
decreased purine and pyrimidine production
What is compensated hemolysis?
Marrow produces more RBCs in face of hemolysis -> higher circulating reticulocyte numbers.
What is the effect of intravascular hemolysis? Cause?
severe and rapid process -> free Hb in circulation, renal toxicity
ex: mismatched blood transfusion
What happens in extravascular hemolysis? Cause?
Insidious process. RBCs in liver or spleen. Hb bound by serum proteins
ex: hereditary spherocytosis
Intracorpuscular vs extracorpuscular hemolytic anemia, inherited or acquired?
Intracorpuscular: inherited (except PNH)
extracorpuscular: acquired
Clinical findings in hemolysis
Pallor Jaundice (elevated bilirubin) Dark Urine (hemoglobin or urobilin) Gallstones (elevated bilirubin) Aplastic crises (exp Parvovirus B19 -> suppression of erythropoiesis)
What is the cause of Hereditary Spherocytosis?
RBC cytoskeletal defects: Band 3, ankyrin, and band 4.2 defects and spectrin deficiency (vertical interaction defect)
Autosomal dominant, poorly penetrant
How is hereditary spherocytosis diagnosed?
Osmotic fragility testing (hypotonic intolerance)
EMA fluorescence test (band 3 deficiency)
Clinical features of hereditary spherocytosis
often presents as neonatal jaundice
aplastic crisis (parvovirus implicated)
gallstones
may need transfusion
How is splenectomy helpful in hereditary spherocytosis and when is it warranted?
eliminates stressful microcirculatory environment, increases RBC lifespan.
warranted if Hb 9 gm% (gram solute / 100g solution)
What defect occurs in hereditary elliptocytosis?
Horizontal defect: spectrin and band 4.1 defect -> reduced RBC lifespan, but milder than spherocytosis
What is Southeast Asian Ovalocytosis?
Band 3 defect -> severe hemolysis
What is Paroxysmal Nocturnal Hemoglobinuria?
Acquired intrinsic RBC disorder
Mutation of PIG-A in stem cell progenitor in marrow -> lack of glycosyl phosphatidyl inositol (GPI) anchor results in loss of CD55 and CD59 -> no inhibition of compliment activation -> MAC induced lysis
What is a common progression of PNH?
Leukemia - premalignant condition
Myelodysplastic sydrome
What is the appearance of bone marrow in PNH?
Hypoplastic with low Fe stores
defective clone -> harm to normal marrow elements -> symptomatic state
What is Budd-Chiari?
Occlusion of IVC or Hepatic vein -> congestive liver disease
May be present in PNH due to platelet abnormality / hypercoagulability
What vessels are often affected in PNH?
Large veins: mesenteric, portal, hepatic
How is G6PD deficiency inherited?
X-linked recessive
What substances can trigger hemolysis in pts with G6PD deficiency?
Antimalarials (Primaquine) Sulpha Nitrofuratoin, chloramphenicol Naphthalene (mothballs) overwhelming infections
What population has the highest frequency of G6PD deficiency?
Blacks - 10% affected
Highest incidence in malarial areas
B-subtype affects caucasians - chronic hemolysis
2 types of autoimmune hemolytic anemia
Warm-reactive: idiopathic, involves IgG
Cold-reactive: associated with infection (mycoplasma, CMV, mono, lymphoma), involves IgM
What is Evan’s Syndrome?
May occur with autoimmune hemolytic anemia
Ab coat platelets -> thrombocytopenia
How is AIHA diagnosed?
Coomb’s tests (direct or indirect)
At what temperature are cold-reactive AIHA antibodies most active?
2-4 degrees C
How is AIHA treated?
Transfusion for low Hb
Protect kidney: alkalinize urine, maintain hydration
Steroids
plasmaphoresis (remove Ab from plasma, controversial)
Splenectomy (last resort)
What are causes of fragmentation hemolysis?
Microangiopathy: as in DIC - fibrin strands produce shear stress
Artificial valves
March hemoglobinuria: repeated trauma - runners, karate, soldiers
Heat denaturation: pre-trasfusion cell warmers
What subunit interface of Hb is particularly important for O2 binding?
a1B2 interface.
Mutations alter O2 affinity
What percent of delivered O2 are tissues able to extract?
25%
What is the P50 of Hb?
O2 tension at which Hb is 50% saturated
Normal ~26 torr
What chromosomes are Hb genes located on?
a: 16
B: 11
What are the forms of hemoglobins in normal adults?
HbA (a2B2) 96%
HbF (a2Y2) 1%
AbA2 (a2d2) 3%
What are the alpha thalassemias?
1 gene deletion: silent carrier
2 gene deletion (cis or trans, cis high risk to offspring): mild anemia
3 gene deletion: HbH disease: hypochromic microcytic anemia w/ splenomegaly (extramedullary hematopoiesis). Moderate anemia.
4 gene deletion: hydrops fetalis, intrauterine death
What Hb tetramers are seen in alpha thalassemia?
Insoluble tetramers formed due to inadequate alpha production
Bart’s Hb: gamma Hb tetramers. only present in first few weeks of live
HbH: Beta tetramers in adults.
Both move faster than reg. Hb on electrophoresis.
What chelation agent is used for B-thalassemia major?
deferioxamine
What does management of B-thalassemia major consist of?
Blood transfusions Chelation Folic acid supplimentation Splenectomy Bone Marrow Transplant
What is Hb like in SC disorder?
2 abnormal B alleles:
HbS and HbC present
Patient produces no HbA
What is Sickle-B-Thalassemia?
Patient with HbS allele and either fully (SB0thal) or partially (SB+thal) suppressed 2nd B allele
Both have elevated HbA2
Both are microcytic
What is the inheritance pattern of sickling hemoglobins?
Codominant
Heterozygous individuals have discernable, but very mild clinical findings.
What is sickle cell Trait?
Heterozygousity for HbS
Rarely symptomatic: heat + dehydration + exercise, high altitude
Always: HbA > HbS
What bones are frequently involved in osteonecrosis in adults with SS disease?
Vertebrae and femur heads
What is acute chest syndrome in SS disease?
Pulmonary infarct or pneumonia caused by vascular occlusion
What is the result of co-inheritance of a-thalassemia with SS disease?
Helpful
Reduces severity of symptoms
What tests are used for diagnosis of Sickle Cell?
Solubility test: Cells lysed by saponin, deoxygenated by N-diathionite. HbS falls out of solution
Electrophoresis: F>S>C>A
What drug is given to Sickle Cell patients to stimulate HbF?
Hydroxyurea - iron chelator, anti-cancer - increases HbF
What occurs in combined HbE / B-thalassemia phenotype?
Transfusion dependent thalassemic phenotype
2 broad groups of WBCs
Phagocytes (granulocytes)
Immunocytes (lymphocytes, plasma cells)
Total number of leukocytes in peripheral blood
4-11x10^9 / L
2 classes of granules in PMN and when in development do they appear?
Primary: Promyelocyte
Secondary: Myelocyte: dominant in mature cells
What are the stages of PMN development and where are those stages found?
Marrow: Myeloblast -> Promyelocyte -> Myelocyte -> Metamyelocyte -> Band -> Neutrophil
Blood: Neutrophil only
Developmental process of monocyte / macrophage
Myeloblast -> Promonocyte -> monocyte (circulating) -> macrophage (tissue)