CH5 - Red Blood Cell Disorders Flashcards
What is Anemia?
Reduction in circulating red blood cell (RBC) mass
How does anemia present?
signs and symptoms of hypoxia
- Color: Pale conjunctiva and skin
- Low Energy: Weakness, fatigue, and dyspnea
- CNS low energy: Headache and lightheadedness
- Heart low energy: Angina, especially with preexisting coronary artery disease
How is RBC mass measured?
Hemoglobin (Hb) = [Hb] in blood
hematocrit (Hct) = Ratio of RBC volume to total blood volume
(Etymology: haemato- + Ancient Greek krites (judge) - blood judge = way of assessing judge)
The percentage (by volume) of packed red blood cells in a centrifuged sample of blood
RBC count = #RBC’s/ volume of blood
Why would Hemoglobin, Hct, and RBC count be normal in a gun shot wound victim?
Heavy blood loss can still result in normal concentration test results because both RBC’s and plasma are lost proportionally. (won’t be reflected in tests until IV fluids given to patient and low RBC mass is diluted out)
All 3 are based on concentration and used as surrogates for RBC mass, which is difficult to measure
Why would Hb, Hct, and RBC count be abnormal in a healthy pregnant woman?
All 3 are based on concentration and used as surrogates for RBC mass, which is difficult to measure. Because they are concentration-based they can sometimes do a poor job of reflecting RBC mass
a woman’s blood volume (plasma) goes up during pregnancy, so her concentrations go down, but her RBC mass is normal.
Anemia is defined as what (in terms of Hb)?
Hb<12.5 g/dL in females - lower because of menstrual blood loss
Hb<13.5 g/dL in males
Normal: 12.5-16.0 g/dl. in females
Normal: 13.5-17.5 g/dL in males
What is the basis for anemia classification?
Based on mean corpuscular volume (MCV)
Normal MCV 80-100
What does the MCV measure?
Average volume of a red blood cell
Microcytic Anemia [Hb]
<80
Normocytic Anemia [Hb]
80-100
Normal size, but [Hb], RBC count are low
Macrocytic Anemia [Hb]
>100
Microcytic anemias are due to
decreased production of Hb
RBC progenitor cells in the bone marrow are?
large and normally divide multiple times to produce smaller mature cells (Normal MCV = 80-100)
Microcytosis is due to?
an “extra” division which occurs to maintain hemoglobin concentration in each RBC despite low [Hb]
Hemoglobin is made of
heme and globin (protein tetramer)
heme is composed of?
Fe
+
porphyrin ring
A decrease in what components leads to microcytic anemia?
1) Fe
2) Protoporphyrin
OR
3)Globin
Microcytic anemias include
(1) Fe deficiency anemia
(2) Anemia of chronic disease (Fe locked in response to chronic inflammatory state via Hepcidin)
(3) Sideroblastic anemia (failure in protoporphyrin synthesis)
(4) Thalassemia (failure in globin synthesis)
Iron deficiency anemia is due to?
↓ Fe -> ↓ heme -> ↓ hemoglobin —» microcytic anemia
What is the most common type of anemia?
iron deficiency anemia
What is the most common nutritional deficiency in the world?
Lack of iron, affecting roughly 1/3 of world’s population
Iron is consumed in what forms?
heme (meat-derived)
and
non-heme (vegetable-derived) forms
Absorption of iron occurs in the?
Duodenum
Enterocytes have heme and non-heme transporters
(DMT1 = Divalent metal transporter 1)
Heme = more readily absorbed
How do enterocytes transport iron?
via DMT1 (Divalent Metal Transporter) on luminal (aka apical)side and into blood via ferroportin on basolateral membrane (opposite of lumen))
Where does transferrin transports iron and where does it take it?
in the blood and delivers it to liver and bone marrow macrophages for storage
Stored intracellular iron is bound to what?
Ferritin = prevents iron from forming free radicals via the Fenton reaction
Followup Lab tests for anemic patient
1) serum iron
2) TIBC
3) % saturation
4) Serum Ferritin
What does the serum iron measure?
Serum iron is a measure of Fe in the blood
What does total iron-binding capacity (TIBC) measure?
How many transferrin molecules in the blood
What does % saturation of iron measure?
percentage of transferrin molecules that are bound by Fe (normal is 33%)
What does serum ferritin measure?
reflects iron stores in macrophages
of
Bone Marrow
and
Liver
What is iron deficiency is usually caused by?
Nutritional deficit
OR
blood loss
MCC of Fe deficiency in infants?
breast-feeding (human milk is low in Fe)
MCC of Fe deficiency in children?
poor diet
MCC of Fe deficiency in adults?
(20-50 years old)—peptic ulcer disease in males
and
menorrhagia or pregnancy in females
MCC of Fe deficiency in elderly?
colon polyps/carcinoma in the Western world;
hookworm (Ancylostoma duodenale and Nieator americanus) in the developing world
What are some other causes of iron deficiency?
1) malnutrition
2) malabsorption
3) gastrectomy - b/c acid aids iron absorption by maintaining the Fe2+ state, which is more readily absorbed
What are the stages of iron deficiency?
- Storage iron is depleted—> decreased serum ferritin> increased TIBC (transferrin)
- Serum iron is depleted— low serum iron; ↓ % saturation
- Normocytic anemia—Bone marrow makes fewer but normal-sized, RBCs
- Microcytic, hypochromic anemia—Bone marrow makes smaller and fewer RBC’s
The initial stage of iron deficiency results in what type of anemia?
normocytic anemia b/c the bone marrow’s initial response is to make as many normal RBC’s as possible, so RBC count goes down, but they are normocytic
what are the clinical features of iron deficiency
anemia
koilonychia = flat fingernails
pica = eating ice
Laboratory findings for iron deficiency include?
- microcytic, hypochromic RBCs with ↑ RDW (red cell distribution width)
- ↓ ferritin; ↑ TIBC; ↓ serum iron; ↓ % saturation
- ↑ Free erythrocyte protoporphyrin (FEP) because not enough Fe to bind up all protoporphyrin rings
What is FEP?
free erythrocyte protoporphoryin - ↓ Fe means less protoporphorin is bound
What is RDW?
red blood cell distribution width, measures the spectrum of size of the RBC’s
What does a low RDW mean?
all of the red blood cells have the same size
What does a high RDW mean?
RBC’s have different sizes
Why do you have increased RDW in iron deficiency?
Initial Bone Marrow response to lower Fe is to produce fewer normal sized RBC’s (normocytic)
After iron deficiency worsens, Bone Marrow starts producing small RBC’s with less Hb (microcytic)
Since RBC’s live 120 days, these varying sizes result in increased RDW
What is the treatment for iron deficiency anemia?
1) Determine underlying cause of Iron Deficiency,
DON’T JUST SUPPLEMENT
2) Supplemental iron (ferrous sulfate) - always
How does the size of the RBC compare to a lymphocyte on a blood smear?
RBC the size of a lymphocyte nucleus
What is Plummer-Vinson syndrome?
A questionable syndrome associated with iron deficiency anemia, esophageal webs, and atrophic glossitis
What is atrophic glossitis?
“Bald tongue” or “beefy tongue”
smooth glossy tongue that is often tender/painful, caused by complete atrophy of the lingual papillae
What is an esophogeal web?
some of the mucosa of the esophagous outfolds potentially creating a partial obstruction in the esophagus -> dysphagia
How Does Plummer-Vinson Syndrome Present?
presents with anemia, dysphagia (food stuck on esophageal webs), and beefy-red tongue (atrophic glossitis)
What is anemia of chronic disease?
Anemia associated with
chronic inflammation
(e.g., endocarditis or autoimmune conditions)
or
Cancer
What is the most common type of anemia in hospitalized patients?
anemia of chronic disease
How is hepcidin related to chronic disease?
chronic disease results in production of acute phase reactants from the liver including hepcidin
What does hepcidin do?
sequesters Fe in storage sites by:
(1) limiting iron transfer from macrophages to erythroblasts
(2) suppressing erythropoietin (EPO) production by kidney
Why did humans evolve to produce hepcidin in response to chronic inflammation?
Just in case, chronic inflammation is due to bacterial infection, to prevent bacteria from accessing Fe, b/c Fe necessary for bacterial survival.
How is anemia of chronic disease related to microcytic anemia?
↓ Fe —> ↓ heme -> ↓ Hb -> microcytic anemia
What are the laboratory findings for anemia of chronic disease?
Ferritin
TIBC
Serum Iron
% Sat
FEP (free erythrocyte protoporphyrin)
↑ Ferritin
↓ TIBC
(b/c High Ferritin causes ↓ transferrin)
↓ serum Fe
↓ % saturation (of transferrin)
↑ FEP
(floating around RBC, free, because not enough Fe to bind with it)
In anemia of chronic disease why is there increased ferritin?
in anemia of chronic disease hepcidin blocks the release of storage Fe from macrophages
- storage Fe builds up meaning ↑ ferritin
Why is there a decrease in serum iron in anemia of chronic disease?
if the bone marrow cannot access the Fe in the macrophages it will deplete the serum Fe bound to transferrin->
↓ % saturation (transferrin)
Why is there increased FEP in anemia of chronic disease?
↓ Fe availability leads to free protoporphyrin since
Hb is composed of
HEME + PROTOPORPHYRIN
Is anemia of chronic classified as normocytic or microcytic?
in the early phase of anemia of chronic disease, the pt first develops a normocytic anemia (just like in Iron Deficiency Anemia) as RBC’s try to pump out fewer but normally sized RBC’s with proper [Hb],
As available Fe becomes severely depleted -> production of microcytic RBCs
What is the treatment of anemia of chronic disease?
Addressing the underlying cause,
exogenous EPO is useful in a subset of patients, especially cancer patients
What is sideroblastic anemia due to?
Defect in protoporphyrin synthesis
How does sideroblastic anemia lead to microcytic anemia?
↓ protoporphyrin -> ↓ Hb -> microcytic anemia
Where are the 7 reactions of the protoporphorin synthesis occuring?
Erythroblasts = RBC progenitor cells located in BM
In both the cytoplasm and Mitochondria
What is the first and rate-limiting step in the production of protoporphyrin?
Aminolevulinic acid synthetase (ALAS) converts
Succinyl CoA -> aminolevulinic acid (ALA)
vit B6 is cofactor for ALAS
What is the rate-limiting step in the synthesis of protoporphyrin?
SCoA -> ALA via ALAS with B6 as a cofactor
What happens after the rate-limiting step in the synthesis of protoporphyrin?
Aminolevulinic acid dehydrogenase (ALAD) converts
aminolevulinic acid (ALA) -> Porphobilinogen
(Additional rxns convert Porphobilinogen -> protoporphyrin)
In the synthesis of Protoporphyrin what happens in the final step?
Ferrochelatase attaches
Protoporphyrin + Fe -> HEME
(occurs in the mitochondria)
How is Heme formed?
Fe transferred from Bone Marrow Macrophages
Fe transferred to Bone Marrow Erythroid precursors (Erythroblasts)
Fe then transferred the Mitochondria to bind with Protoporphyrin to form HEME
What happens if protoporphyrin is deficient?
Fe remains trapped in Erythroblast mitochondria
What is seen when Fe gets trapped in the Mitochondria?
Fe-laden mitochondria form a ring around the nucleus of Erythroblasts (visualized using Prussian Blue Stain)
Erythroblasts with rings of Fe-laden Mitochondria surrounding the nucleus are called ringed sideroblasts
(hence, the term sideroblastic anemia)
Where does sideroblastic anemia get its name?
The ring around the nucleus of erythroid precursors of iron laden mitochondria is called ringed sideroblasts
Ancient greek = sídēros, “iron”
Latin = sideris “constellation”
Constellation fo Fe around nucleus
Is sideroblastic anemia congenital or acquired?
Can be BOTH:
congenital or acquired
Describe the Most Common Congenital form of Sideroblastic Anemia?
most commonly involves mutation in ALAS
(rate-limiting enzyme)
What are the acquired causes of sideroblastic anemia?
1) Alcoholism
2) Lead poisoning
3) Vitamin B6 deficiency
How can alcoholism lead to sideroblastic anemia?
EtOH = mitochondrial poison
- >damages production of protoporphyrin
- > sideroblastic anemia
How does lead poisoning lead to sideroblastic anemia?
Pb DENATURES
enzymes, including
ALAD (Protoporphyrin synthesis)
and
Ferrochelatase (binds Fe to Protoporphyrin)
How does Vitamin B6 deficiency lead to sideroblastic anemia? This is most commonly seen as a side effect of what treatment?
Required cofactor for ALAS
(first and rate-limiting step in Protoporphyrin synthesis)
What patients get Vit B6 deficiency, and what kind of anemia can they develop?
most commonly seen as a side effect of
isoniazid treatment for Tuberculosis
Sideroblastic anemia b/c Vit B6 is a cofactor for ALAS (rate limiting step in protoporphyrin synthesis)
In sideroblastic anemia why is there increased ferritin?
Fe builds up in the Bone Marrow Erythroid Precursor (Erythroblast)
A ton of Fe loaded in Erythroblast Mitochondria
Unbound Fe generates so many free radicals
Erythroblast damaged and dies
Fe leaks out of dead Erythroblast into BM and Serum
- > leaked Fe consumed by Bone Marrow Macrophages
- > high stores of Fe (increased ferritin)
Not enough Protoporphyrin to bind all of the Fe, so Fe accumulates
What are the laboratory findings for sideroblastic anemia?
Ferritin
TIBC
Serum Fe
% saturation
↑ Ferritin
(BM Macrophages store Fe leaked from dead Erythroblasts)
↓ TIBC
(in response to high Ferritin)
↑ serum Fe
(Fe leaked from dead Erythroblasts)
↑ % saturation
(Fe binds up transferrin at higher than normal 30% rate)
Why is there increased percent saturation in sideroblastic anemia?
In iron-overloaded state there is also Fe leakage into serum
Leads to ↑ percent saturation (transferrin)
How are hemochromatosis patients similar to sideroblastic anemia patients?
Both are iron overloaded states
similar lab values
what is a characteristic of the carriers of thalassemia?
it is an inherited mutation
carriers protected against Plasmodium falciparum malaria
Sickle cell carriers also protected from severe malaria due to Plasmodium falciparum)
What are normal lab findings for
TIBC
Serum Iron
% Saturation
TIBC - 300pg/dL
Serum Iron - 100pg/dL (1/3 of TIBC)
% Saturation - 33% (1/3 of TIBC)
Regarding microcytic anemia what are the lab values for Iron Deficiency Anemia?
Ferritin - ↓
TIBC - ↑
Serum Iron - ↓
% Saturation- ↓
Regarding microcytic anemia what are the lab values for Anemia of Chronic Disease?
Ferritin- ↑
TIBC - ↓
Serum Iron- ↓
% Saturation- ↓
Regarding microcytic anemia what are the lab values for sideroblastic anemia?
Ferritin - ↑
TIBC - ↓
Serum Iron - ↑
% Saturation - ↑
What are lab values for
TIBC
% Saturation
seen with pregnancy and oral contraceptives?
TIBC- ↑
b/c liver ↑ production of transferrin
% Saturation- ↓ (because of ↑TIBC )
What is thalassemia?
Anemia due to decreased synthesis of the globin chains of hemoglobin
How is thalassemia divided?
Alpha
vs.
Beta
thalassemia
based on DECREASED production of
alpha vs beta globin chains
How is thalassemia related to microcytic anemia?
dec globin -> dec hemoglobin —> microcytic anemia
What are the normal types of hemoglobin?
HbF = Fetal Hemoglobin
(α2 and γ2)
HbA
(α2 and β2)
and
HbA2
(α2 and δ2)
What is alpha-Thalassemia usually due to?
Gene DELETION
Normally
4 αlpha alleles present
on chromosome 16
(2 on mom’s copy of Ch 16 and 2 on dad’s copy of Ch 16)
In alpha thalassemia what are the symptoms when one gene is deleted?
asymptomatic - 3 copies remain
In alpha thalassemia what are the symptoms when two genes are deleted?
mild anemia
with
slight ↑ RBC count
cis deletion - both copies knocked out on one chromosome
trans deletion - the 2 deleted alleles are on different copies of Ch 16
In alpha thalassemia what are the symptoms when cis deletion occurs?
it is when both deletions occur on the same chromosome; seen in Asians -
believed to be responsible for higher rate of spontaneous abortions in Asia
In alpha thalassemia what are the symptoms when trans deletion occurs?
mild anemia
with
slight ↑ RBC count
it is when one deletion occurs on each chromosome; seen in Africans, including African Americans (increased probability of carrier status in offspring-> protecting against Plasmodium falciparum)
Which is worse cis or trans deletion in alpha thalassemia?
Cis because it is associated with an increased risk of severe thalassemia in offspring, because 50% chance that offspring will get Ch 16 with both alpha globin alleles deleted.
If partner also has at least one defective copy, strong risk of severe thalassemia
In alpha thalassemia what are the symptoms when three genes are deleted?
No problem in utero. One copy enough to produce HbF.
Severe Anemia after birth
as HbA, and HbA2 production begins.
beta dimers (b/c low alpha dimers) combine to form tetramers (HbH) that damage RBCs
HbH is seen on electrophoresis
In alpha thalassemia what are the symptoms when four genes are deleted?
lethal in utero (hydrops fetalis = serious fetal condition defined as abnormal accumulation of fluid in two or more fetal compartments)
HbF not possible without alpha chains, so
gamma chains form tetramers (Hb Barts) that damage RBCs
Hb Barts seen on electrophoresis
What is Hb Barts?
it is a tetramer of gamma chains in Fetus
What is the difference between beta and alpha thalassemia?
Alpha is due to Alpha gene deletions
Beta is due to Beta gene mutations
Beta-Thalassemia is usually due what?
to gene mutations (point mutations in promoter or splicing sites); seen in individuals of African and Mediterranean descent
Where are beta genes present?
One beta allele present on each copy of Ch 11
Mutations result in either
complete knock out of Beta allele ( β0 - Beta Null)
or
Diminished ( β+) production of the β-globin chain
Results in spectrum of severity
β β+ - Beta Thalassemia Minor
β+/β+
β+β0
β0 β0
What is the difference between β0/ β+?
β0 is the complete inability to produce beta chain,
β+ is decreased production of beta chain
ß-thalassemia minor
(β/β+ - one normal beta and one decreased production of beta)
is the mildest form of disease
usually asymptomatic with an increased RBC count
In ß-thalassemia minor, what is seen on blood smear?
microcytic
hypochromic RBCs
target cells are seen on blood smear
In ß-thalassemia minor, what is seen on hemoglobin electrophoresis?
It shows slightly ↓ HbA
↑ HbA2 (5%, normal 2.5%)
↑ HbF (2%, normal 1%)
Why are target cells seen with Beta Thalassemia Minor?
Because Hb production is down, the RBC is not very densely packed, so some membrane forms a bleb in the middle where normally there is narrowing.
Hb accumulates in this bleb
ß-Thalassemia major
(ß0/ß0) is the most severe form of disease and
How does ß-Thalassemia major present?
with severe anemia a few months after birth;
high HbF (α2γ2) at birth is temporarily protective
In ß-Thalassemia major, why is there ineffective erythropoiesis?
alpha tetramers aggregate and damage RBCs as they are produced
removal by splenic macrophages of circulating RBCs by the spleen
In ß-Thalassemia major, why is there extravascular hemolysis?
removal by splenic macrophages of circulating RBCs by the spleen, as they recognize abnormal α-tetramers
What is ineffective erythropoesis in ß-Thalassemia major?
damage to the red blood cells as they are being generated by precipitated Hb caused by alpha tetramers
What is extravascular hemolysis in ß-Thalassemia major?
removal of circulating RBCs by the spleen
Why do the patients with ß-Thalassemia major develop massive erythroid hyperplasia?
Severe anemia causes massive EPO production by kidney
Why is there expansion of hematopoiesis into the skull in ß-Thalassemia major?
Severe anemia ->
massive EPO increase from kidney ->
BM hyperplasia
and
erythropoiesis expansion beyond axial skeleton and into skull and facial bones
and
Extramedullary hematopoesis
(Liver and Spleen)