Disorders of Red Blood Cells
Professor Myat Thandar
Department of Physiology
University of Medicine 1
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Functions of RBCs
 O2 transport (Hb in the RBCs)
 CO2 transport
 Acid-base balance
2
Functional Importance of the Biconcave
Shape of RBCs
 Larger surface area for O2 diffusion
 Thinness of cell membrane enables O2 to diffuse easily
 Flexibility of membrane facilitates the transport function
3
Network of Fibrous Proteins of RBCs
 Spectrin and Ankyrin
 Imparts elasticity and
stability to membrane and
allows RBCs to deform
easily
4
Haemoglobin
 A natural pigment,
reddish when
oxygenated
 4 polypeptide chains
(a globin portion and
a heme unit)
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Haemoglobin F in Fetus
 Higher affinity for O2
than adult Hb
 HbF is replaced
within 6 months of
birth with HbA
6
Haemoglobin Synthesis
 Availability of iron for
heme synthesis
 Amount of iron: 2 g in
women and 6 g in men
Clinically, decreased ferritin levels
usually indicate the need for prescription
of
iron supplements.
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Red Cell Production
 Until 5, almost all bones; After 20, membranous bones
 Approximately 1% of total RBC is generated from bone marrow
each day
 Reticulocyte count serves as an index of erythropoietic activity of
bone marrow
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Stages of Erythropoiesis
Hematopoietic stem cell (HSCs)
IL-1, IL-6, IL-3 (interleukins)
GM-CSF, G-CSF, SCF
Unipotent committed stem cell
Erythropoietin
GM-CSF
Proerythroblast (15-20 mm)
Early normoblast (12-16 mm)
Intermediate normoblast (10-14 mm)
Haemoglobinization begins
Late normoblast (10-14 mm)
Haemoglobinization ++
Nuclear disintegration
Reticulocyte (7-8 mm)
-Haemoglobinization ++
Nucleus remains only as strands of reticular element
Erythrocyte (7.5 mm)
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Red Cell Production
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Red Cell Maturation
 Reduction in the cell size
 Increase in the amount of haemoglobin
 Disappearance of nucleus, and
 Change in staining characteristics of cytoplasm: basophilic to
eosinophilic. This is partly due to a fall in content of RNA.
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Erythropoietin
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Human Erythropoietin
Produced by recombinant DNA
technology
Used for anaemia induced by
chemotherapy in cancer patients, and
HIV infected persons treated with
zidovudine
In severe anaemia, retic count may
be as much as 30% (normal about
1%); numerous erythroblasts may
appear in the blood
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Destruction of Red Blood Cells
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Excretion of Bilirubins
Excess bilirubin elimination leads to
bilirubin gallstones
If red cell destruction and bilirubin
production is excessive, yellow
discoloration of the skin, jaundice,
occurs due to accumulation
of unconjugated bilirubin
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Haemoglobinuria
 Haemoglobin binding protein – Haptoglobin – in the plasma
 Other plasma proteins – albumin – also binds to Hb
 Extensive destruction of RBCs (haemolytic transfusion
reactions), binding capacity is exceeded
 Haemoglobinaemia and haemoglobinuria results
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Red Cell Metabolism
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2,3-DPG decreases affinity of Hb for O2, facilitating the release of O2 at
tissue levels
Increased 2,3-DPG occurs in chronic hypoxia such as chronic lung
diseases, anemia and residence at high altitude
Inhibition of Oxygen Haemoglobin
Binding
Certain chemicals : nitrates and sulfates
Hb reacts with nitrite to form methaemoglobin
G6PD deficiency predisposes to oxidative denaturation of hemoglobin
with resultant red cell injury and lysis (oxidative stress generated by
infection or exposure to certain drugs)
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Laboratory Tests
 Using automated blood cell counters: red cell content and
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indices
Red cell indices are used to differentiate type of anemias
by size or color of red cells
Haemoglobin
Hematocrit
Mean corpuscular volume (MCV falls in microcytic and rises
in macrocytic anemia)
Mean corpuscular haemoglobin concentration
(normochromic or normal MCHC; hypochromic or
decreased color or decreased MCHC)
Laboratory Tests
 Mean cell haemoglobin
 A stained blood smear: information about size, color and
shape of red cells and the presence of immature or abnormal
cells
 If blood smear is abnormal, bone marrow examination may
be indicated
 Bone marrow aspiration from posterior iliac crest or the
sternum
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Red cell count and Haemoglobin
severity of anemia
Red cell characteristics
Size
Color
Shape
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normocytic, microcytic or macrocytic
normochromic, hypochromic
the cause of anemia
Anemia
 Values of hemoglobin, hematocrit or RBC counts which are
more than 2 standard deviations below the mean
 HGB<13.5 g/dL (men)
 HCT<41% (men)
<12 (women)
<36 (women)
Normal Hb Concentration
Male
Female
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:
:
Western value
16 g / dL (14 - 17 g/dL)
14 g / dL (12 - 15.5 g/dL)
Myanmar value
14.4 g / dL
12.5 g / dL
Pathophysiology of Anemia
 Blood Loss
 Decreased Production (lack of nutritional elements or bone
marrow failure)
 Increased Destruction (haemolysis)
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Effects of Anemia
 Manifestations of impaired oxygen transport and the resultant
compensatory mechanisms
 Reduction in red cell indices and hemoglobin levels
 Signs and symptoms associated with the pathophysiologic
process that causes anemia
Manifestations depend on its severity, the rapidity of
its development and the person’s age and health status
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Symptoms of Anemia
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Impaired oxygen transport and tissue
hypoxia
 Weakness, fatigue, dyspnoea and angina
 Brain hypoxia results in headache, faintness and dim vision
 Redistribution of blood results in pallor of skin, conjunctiva,
mucous membranes and nail beds
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Compensatory Mechanisms
 Tachycardia, palpitations and increased cardiac output
 A flow type of systolic murmur
 Ventricular hypertrophy and high output heart failure
 Accelerated erythropoiesis results in diffuse bone pain and
sternal tenderness
Haemolytic anemia : jaundice
Aplastic anemia : petechiae and purpura due to reduced platelet functions
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Blood Loss Anemias
 Depends on rate of haemorrhage and blood loss is external
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or internal
Rapid loss causes circulatory shock and collapse; fall in red
cell count, Hb, hematocrit due to fluid shift into vessels
Initially red cells are normocytic, normochromic
Increased erythropoietin and retic count
Slow loss (GI bleeding, menstrual disorders) causes anemia;
signs and symptoms develop if the amount of red cell mass
loss reach 50% (Hb <8 g/dL)(iron deficiency anemia)
External bleeding leads to iron loss and iron deficiency
Haemolytic Anemias
 Characterized by premature destruction of red cells,
retention in the body of iron and other products of Hb
destruction and increased erythropoiesis
 Normocytic normochromic red cells
 Increased retic count in the circulating blood
 Haemoglobinemia, haemoglobinuria, jaundice,
haemosiderinuria
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Haemolytic Anemias
 Intravascular haemolysis is less common, caused by
complement fixation in transfusion reactions, mechanical
injury or toxic factors
 Extravascular haemolysis occurs when RBCs are less
deformable to traverse splenic sinusoids, characterized by
anemia and jaundice
 Intrinsic : defects of red cell membrane,
haemoglobinopathies (sickle cell disease and thalassemias)
and enzymes defect
 Extrinsic or acquired : drugs, bacteria and other toxins,
antibodies and physical trauma
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Inherited Disorders of Red Cell Membrane
 Hereditary spherocytosis : abnormalities of spectrin and
ankyrin
 Mild hemolytic anemia, jaundice, splenomegaly and bilirubin
gallstones
 Splenectomy done to reduce red cell destruction and blood
transfusion in a crisis
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Sickle Cell Disease
 Haemoglobin S (point mutation in
the β chain of Hb, valine for
glutamic acid)
 Haemolytic anaemia, jaundice,
gallbladder stones, pain and organ
failure (infarction of organs)
 Hb S becomes sickled when
deoxygenated or at a low oxygen
 Deoxygenated Hb aggregates and
polymerizes in the cytoplasm,
creating a semisolid gel that
changes the shape and
33 deformability of the cell
Red Cell Sickling
 Chronic hemolytic anemia
 Blood vessel occlusion
 Associated conditions: cold,
stress, physical exertion, infection,
illnesses that cause hypoxia,
dehydration or acidosis
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Features of Sickle Cell Disease
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Diagnosis and Treatment
 Neonates : clinical findings and haemoglobin
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electrophoresis
Prenatal diagnosis : analysis of fetal DNA by amniocentesis
Prevention of sickling episodes, symptomatic treatment and
treatment of complications (prophylactic penicillin and full
immunization)
Cytotoxic drug – hydroxyurea – to allow synthesis of more
HbF and less HbS
Nitric oxide appears to be a promising new drug
Bone marrow or stem cell transplantation
Thalassemias
 Inherited disorders of haemoglobin synthesis and decreased
synthesis of α or β globin chains of HbA
 Heterozygous or homozygous
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Thalassemias
 β thalassemias – Cooley anaemia or Mediterranean anemia
– common in Mediterranean population of southern Italy
and Greece
 α thalassemias more common among Asians
 Anemia due to low production of affected chain and
continued production and accumulation of unaffected
globin chain
 Reduced Hb synthesis leads to hypochromic microcytic
anemia; accumulation of unaffected chain interferes with
normal red cell maturation, and membrane changes leading
to hemolysis and anemia
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β - thalassemias
 Excess α chains are
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denatured to form
precipitates (Heinz bodies)
in the bone marrow red cell
precursors
 Heinz bodies impair DNA
synthesis and damage to red
cell membrane
 Coagulation abnormalities,
thrombotic events (stroke
and pulmonary embolism)
in moderate to severe form
Pathophysiology of β - thalassemias
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Thinning of cortical bones
Treatment of β - thalassemias
 Regular transfusion to maintain Hb at 9 to 10 g/dL
 Iron chelation therapy to reduce iron load
 Stem cell transplantation
 Stem cell gene replacement
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α - thalassemias
 Synthesis of globin chains is controlled by 4 genes
 Deletion of single gene : silent carrier; two genes is α
thalassemia trait
 Deletion of three genes leads to unstable aggregates of α
chains – HbH
 Four globin chains are deleted : Hb Bart (extremely high
oxygen affinity, cannot release oxygen in the tissues
 Chronic hemolytic anemia
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Inherited Enzymes Defect
 G6PD deficiency
 RBCs vulnerable to oxidants, direct oxidation of Hb to
methaemoglobin, and denaturation of Hb to form Heinz
bodies
 Anti-malaria drug primaquine, the sulfonamides,
nitrofurantoin, aspirin, phenacetin, some
chemotherapeutics and other drugs cause hemolysis
 Diagnosed through G6PD assay or screening test
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Acquired Hemolytic Anaemias
 By direct membrane destruction or antibody mediated lysis
 Various chemicals, toxins, venoms, malaria infection,
prosthetic heart valves, vasculitis, severe burns, septicaemia,
thrombotic thrombocytopenic purpura, renal disease
 Warm reacting antibodies (IgG) and cold reacting
antibodies (IgM)
 Warm antibodies bind with Ag on red cell membrane (Rh
Ag), resulting in spherocytosis and destruction by RE
system
 Cold antibodies activate complements; as in
lymphoproliferative disorder and idiopathic
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Rh incompatibility
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Coomb’s Test
 Direct Antiglobulin Test (DAT) is positive in autoimmune
hemolytic anaemia, erythroblastosis fetalis, transfusion
reactions, transfusion reactions and drug induced hemolysis
 Indirect antiglobulin test is used for antibody detection and
crossmatching before transfusion
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Anemias of Deficient Red Cell Production
 Deficiency of nutrients for hemoglobin synthesis (iron)
 Deficiency of nutrients for DNA synthesis (Cobalamin or
folic acid)
 Marrow is replaced by nonfunctional tissues
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Iron Deficiency Anemia
 Dietary deficiency (vegetarians)
 Loss of iron through bleeding (peptic ulcer, polyps, cancer,
menstrual bleeding)
 Increased demands (growing children, pregnancy)
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Iron Metabolism
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Characteristics of Iron Deficiency Anemia
 Low haemoglobin and hematocrit
 Decreased iron stores, low serum iron and ferritin
 Red cells number decreased and are microcytic and
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hypochromic
Poikilocytosis (irregular shape)
Anisocytosis (irregular size)
Reduced MCHC and MCV
Membrane changes predispose to
hemolysis
Manifestations of Iron Deficiency Anemia
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Treatment of Iron Deficiency Anemia
 Prevention and treatment of
the cause
 Ferrous sulfate
 Parenteral iron (iron dextran
or sodium ferric gluconate)
 Initial test dose to prevent
severe anaphylactic reactions
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Megaloblastic Anemia
 Impaired DNA synthesis
 Enlarged red cells (MCV >100 fL)
 Develop slowly
 Vitamin B12 and folic acid
deficiency
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Vitamin B12 Deficiency Anemia: B12
Absorption
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Pernicious Anemia
 Atrophic gastritis
 Autoimmune
destruction of gastric
mucosa
 Gastrectomy, ileal
resection, inflammation
or neoplasms in
terminal ileum,
malabsorption
syndrome
 MCV elevated; MCHC
is normal
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Vitamin B12 Containing Food
Normal body stores of
1000 to 5000 µg provide
the daily requirement of
1 µg for a number of
years.
Therefore, deficiency
develops slowly
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Diagnosis of B12 Deficiency
 The Shilling test – 24 hour urinary excretion of radiolabelled
vitamin B12 administered orally
 Detection of parietal cell and intrinsic factor antibodies
 Lifelong intramuscular or high oral doses of vitamin B12 is
required
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Folic Acid
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Folic Acid Deficiency
Total body stores amount to 2000 to 5000 µg and 50µg is required
in the daily diet. A dietary deficiency may result in anaemia in a few months
Pregnancy increases the need for folic acid 5 to 10 fold
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Aplastic Anemia
 Reduction of all 3 hemopoietic cell lines
 Onset may be insidious but may be abrupt and severe
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Therapy in Aplastic Anemia
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Therapy in Aplastic Anemia
 Immunosuppressive therapy with lymphocyte immune
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globulin
Avoid offending agents
Antibiotics for infection
Red cell transfusion to correct anaemia
Platelets and corticosteroid therapy to minimize bleeding
Chronic Disease Anemia
 Occur as a complication of chronic infections, inflammation,
cancer and chronic kidney diseases
 Short red cell life span; deficient red cell production; a
blunted response to erythropoietin, and low serum iron
 Mild anemia – normocytic and normochromic – with low
reticulocyte counts
 In chronic renal diseases, uremic toxins and retained nitrogen
interfere with actions of erythropoietin; hemolysis and blood
loss associated with hemodialysis and bleeding tendencies
also contribute to anemia
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Therapy in Chronic Disease Anemia
 Short-term erythropoietin therapy
 Iron supplementation
 Blood transfusions
 In future – iron chelating agents and cytokines to stimulate
erythropoietin production
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