Red Blood Cells
1
Hemoglobin: Structure, Function & Disorders
HEMOGLOBIN
STRUCTURE:
Hemoglobin is the oxygen carrying protein of red blood cells responsible for the
red color characteristic of these cells. The amount of hemoglobin (Hb) present in red
blood cells differs in males and females and varies also with age. Each hemoglobin
molecule consists of 4 subunits and each subunit consists of a polypeptide chain
conjugated to a heme moiety. Heme is an iron-containing porphyrin derivative and the
polypeptides chains are collectively called globins. The 4 subunits of normal Hb are
arranged as two pairs of different polypeptide chains. In normal adults, one pair of
polypeptide chains is called the  chains, each of which contains 141 amino acids and the
other pair is called the  chains, each consisting of 146 amino acids. Thus the structure of
normal adult Hb, known as Hb-A, can be designated as 22.
In adults, a small proportion of another type of Hb is also present, Hb-A2, representing
about < 2.5% of the total Hb in blood. Instead of  chains, Hb-A2 contains another type
of polypeptide chain called , which is similar to  but contains 10 different amino acid
residues. Different hemoglobins are present in embryonic and fetal stages.
Derivatives of Hb-A are also present in small amounts in normal blood. In one derivative
called Hb-A1c the hemoglobin is glycosylated where glucose is attached to the terminal
valine residue in each  chain. Hb-A1c is elevated in patients with diabetes mellitus and is
an indicator of the glucose levels in the preceding weeks to months.
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Red Blood Cells
2
Hemoglobin: Structure, Function & Disorders
HEMOGLOBIN SYNTHESIS:
Heme synthesis:
Heme synthesis occurs both in the cytosol and mitochondria in a series of enzymatically
controlled steps that begins with the condensation of glycine and succinyl-CoA to form
the first intermediary product -aminolevulinic acid. All successive steps are catalyzed by
specific enzymes, the deficiency of each one leads to a group of disorders called
Porphyria. The various steps of heme synthesis, the enzymes involved, and the disorders
with their manifestations are shown in the figure below.
[This picture is adapted from BLOOD: Principles & Practice of Hematology by Handin et al. Lippincott Press]
The enzymes ALA Dehydratase & Ferrochetalase are inhibited by lead (Pb) that causes
anemia in chronic lead poisoning, especially in children living in old houses with lead
paint.
[This picture is adapted from BLOOD: Principles & Practice of Hematology by Handin et al. Lippincott Press]
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material for teaching purposes only. No commercial incentives are sought or intended.
Red Blood Cells
3
Hemoglobin: Structure, Function & Disorders
Globin synthesis:
The two pairs of hemoglobin molecules are derived from two gene clusters: the  globin
gene cluster and the  globin gene cluster. The  globin gene cluster contains the  gene,
2 and 1 genes and the  globin gene cluster contains the , G, A, 
 genes.
During embryonic stages of development, the  gene of the -chain gene complex
associates with  and  chains of the  globin gene complex form Hb-Gower 1 & 2,
which are embryonic hemoglobins. Another embryonic hemoglobin called Hb Portalnd is
formed by association of  &  chains. The various hemoglobins are also shown below.
[The above picture is adapted from BLOOD: Principles & Practice of Hematology by Handin et al. Lippincott Press]
The contents & pictures in this handout are derived from various sources including books, journal articles and patient
material for teaching purposes only. No commercial incentives are sought or intended.
Red Blood Cells
4
Hemoglobin: Structure, Function & Disorders
The sequence of expression of various chains of hemoglobin during various stages
development is shown below.
[This picture is adapted from BLOOD: Principles & Practice of Hematology by Handin et al. Lippincott Press]
HEMOGLOBIN DEGRADATION:
After an intravascular or an extravascular hemolysis or when old red blood cells are
destroyed in the reticuloendothelial system, the globin portion of the hemoglobin
molecule is split off and the heme is converted to biliverdin and finally to bilirubin.
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material for teaching purposes only. No commercial incentives are sought or intended.
Red Blood Cells
5
Hemoglobin: Structure, Function & Disorders
HEMOGLOBIN FUNCTION:
The main function of hemoglobin is to carry oxygen from lungs to peripheral tissues in
the form of oxyhemoglobin; O2 attaches to the Fe+2 in the heme. This function is
achieved by cooperative association of O2 with the heme moiety. The association of
oxygen with heme and hence O2 saturation at a given O2 tension is governed by several
factors including pH, temperature and the concentration of 2,3-DPG in red cells as shown
below.
The affinity of Hb-F for oxygen is greater than Hb-A. Nature has provided this property
to Hb-F to facilitate movement of oxygen from maternal to the fetal circulation. From 828 weeks of gestation, Hb-F is the predominant form, accounting for almost all of the
hemoglobin. The red cells of newborns, however, start forming Hb-A such that they have
about 80% Hb-F and ~20% Hb-A and <0.5% Hb-A2. After 6 months of age, Hb-F is
usually <1% of total hemoglobin. In some individual, however, fetal Hb persists long
after without any clinical symptoms, a condition called hereditary persistence of fetal
hemoglobin (HPFH). Hb-F is also increased as a compensatory mechanism in conditions
causing decreased output of normal  chains such as sickle cell anemia, Hb-C disease, thalassemia, and other conditions of  chains. The embryonic hemoglobin forms also
have oxygen affinity similar to Hb-F.
When blood is exposed to various drugs and other oxidizing agents, the ferrous iron that
is normally in the molecule is converted to ferric iron, forming methemoglobin. This Hb
is darker in color and causes a dusky discoloration of the skin resembling cyanosis. Some
oxidation of Hb to methemoglobin occurs normally, but an enzyme system in red cells,
the NADH-methemoglobin reductase system, converts methemoglobin back to normal
Hb. Congenital absence of this enzyme is one cause of hereditary methemoglobinemia.
Carbon monoxide (CO) can also react with Hb to form carboxyhemoglobin. The affinity
of CO is much greater for Hb than oxygen. This is why CO easily displaces O2 on Hb,
thus reducing oxygen capacity of blood.
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Red Blood Cells
6
Hemoglobin: Structure, Function & Disorders
DISORDERS OF HEMOGLOIBIN:
These are simply of two kinds
A. Quantitative – called Thalassemias, and
B. Qualitative – called Hemoglobinopathies
THALASSEMIA:
They are simply the result of reduced output of one or more globin chains and can be
classified based on the type of globin chain deficiency. A total lack of synthesis of a
chain is symbolized as 0 such as , and , whereas partial lack of a normal chain
is characterized by a + sign such as , , , and . The genetic defects are either a
deletion of the gene (partial or total) or any one or more of a variety of non-deletion
mutations such as base substitutions in the gene itself or any of the regulatory regions.
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material for teaching purposes only. No commercial incentives are sought or intended.
Red Blood Cells
Hemoglobin: Structure, Function & Disorders
Clinical syndromes:
Clinically all the thalassemia mutations can be categorized as follows:
Clinically and hematologically normal:
(Silent carrier state)
1. –
2. cs
3. 
/A
Microcytosis with little or no anemia:
(Thalassemia minor)
  (Asian type)
2.  (African type)
3. cs/cs
4. 0/A
5. Lepore/A
Microcytosis with moderate anemia:
(Thalassemia intermedia)
1. African/African
2. 0 or + with  or 
3. ()o/()o
4. Lepore/Lepore
Microcytosis with marked anemia:
(Thalassemia major- <2 years of age)
1. 0/0
2. Medit/Medit
Hemolytic anemia and microcytosis:
(Hemoglobin H disease)
 
2. cs
Lethal defects:
(Hydrops fetalis)
1.  for  genes
2. mutants
3. ()0/()0
 and  thalassemia:
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material for teaching purposes only. No commercial incentives are sought or intended.
7
Red Blood Cells
8
Hemoglobin: Structure, Function & Disorders
See Robbins Pathologic Basis of Disease for a detailed description of each.
HEMOGLOBINOPATHIES:
These are the functional abnormal forms of hemoglobin and some of them are described
in a table at the end of this handout. For sickle cell anemia see Robbins Pathologic basis
of Disease.
-Chain Abnormalities:
-thalassemias1.
2.
3.
4.
A/GA : no effect or slight hypochromia of fetal RBCs. Asymptomatic in adults.
GA : mild hypochromia & microcytosis of fetal RBCs. Asymptomatic in adults.
G or A : Moderate to severe fetal anemia with microcytosis.
 for -chains : incompatible with life.
-hemoglobinopthies

abnormal -Hb represents 10-20% of total Hb in the heterozygous states.
No hematologic abnormalities except in Hb-F Poole, which presents with neonatal
Heinz body hemolytic anemia.
Unstable Hemoglobinopathies
 Several Hb variants that are unstable at high temperature (50 oC) and form a
precipitate.
 About 100 variants have been described. About 75% are -chain variants and 25%
are -chain variants.
 Heinz bodies (denatured Hb) are present in RBCs in most but not all cases.
 Patients usually present in early childhood with a hemolytic anemia, jaundice, and
splenomegaly.
 Prominent basophilic stippling present.
 Red cell abnormalities are more pronounced after splenectomy.
1. Hb-Koln
2. Hb-Zurich
3. Hb-Indianapolis
4. Hb-Mississippi
5. Hb-Leiden
6. Hb-Gun Hill
7. Hb-Sydney
8. Hb-Bristol
9. Hb-Istanbul
10. Hb-Geneva
The contents & pictures in this handout are derived from various sources including books, journal articles and patient
material for teaching purposes only. No commercial incentives are sought or intended.
Red Blood Cells
Hemoglobin: Structure, Function & Disorders
The contents & pictures in this handout are derived from various sources including books, journal articles and patient
material for teaching purposes only. No commercial incentives are sought or intended.
9
10
Thalassemias
Thalassemia
type

0A
African +African


Medit+Medit
A
+
Lepore

/Lepore
Lepore A

/
S
+S
C
C
E
E




thal
thal






CSCS
CS
CS
Genetic defect
Point mutations; deletions
Point mutations; deletions/Hb-A
Point mutations
Point mutations
Point mutations
Point mutations; deletions/Hb-A
Point mutations
Point mutations
Point mutations; deletions/Hb-S
Point mutations/Hb-S
Point mutations; deletions/Hb-C
Point mutations/Hb-C
Point mutations; deletions/Hb-E
Point mutations/Hb-E
Deletions
Deletions
Deletions
Deletions
Point mutations
Deletions
Various defects.
Deletion. Point mutations.
Deletion. Point mutations.
Deletion. Point mutations.
Deletion. Point mutations.
Deletions, with or without  gene
Deletions and mutations
Chain elongation mutation
Deletions and mutations
Hb
g/dl
2-7
7-10
7-10
2-7
>10
2-7
2-7
>10
7-10
9-12
7-10
>10
2-7
7-10
9-10
>12
7-10
Normal
Normal
Normal
10-12
10-12
7-10
3-6
9-10
Normal
5-7
MCV
fl
50-60
50-70
60-70
50-60
70-80
50-60
50-60
70-80
60-70
~70
60-70
70-80
50-60
60-70
>80
70-80
60-70
Normal
Normal
75-85
65-75
65-75
55-65
110-120
Normal
-
Hb-A
Hb-A2
Hb-F
Clinical features/Comments
0
~90%
~65%
5-30%
~90%
2-10%
0
90%
0
5-40%
0
5-40%
0
5-40%
0
80%
>95%
Normal
Normal
Normal
~85%
~85%
~65%
0
Normal
-
2-8%
3.5-8%
2-8%
2-8%
3.5-8%
3.5-5%
0
1.5-3%
3.5-5%
3.5-7%
3.5-5%
3.5-5%
3.5-5%
3.5-5%
0
<2%
normal
0
Normal
Normal
1.5-3%
1.5-3%
<2%
0
Normal
-
>94%
1-5%
20-30%
60-90%
1-5%
>85%
80-90%
3-5%
1-5%
1-5%
1-5%
1-5%
1-5%
1-5%
100%
5-15%
normal
Normal
low
Normal
<1%
<1%
<1%
0
Normal
-
Thalassemia major. Mild at birth to 6 month of age. Premature death.
Thalassemia minor.
Thalassemia intermedia (African type).
Thalassemia major (Mediterranean type ).
Thalassemia minor.
Thalassemia major. Mild at birth to 6 month of age.
Thalassemia major. Hb-Lepore (-fusion protein) = 10-20%
Thalassemia minor. Hb-Lepore (-fusion protein) = 2-5%
Clinical severity like SS-disease. >90% Hb-S. Target & SS cells.
Severity depends upon level of hemoglobin A. 60-70% Hb-S
Thalassemia major. Hb-C = 95%
Thalassemia intermedia. Hb-C = 60-70%
Thalassemia major. Hb-E = 95%
Thalassemia intermedia. Hb-E = 60-70%
Thalassemia intermedia. High Hb-F thalassemia.
Thalassemia minor. High Hb-F thalassemia. Heterocellular Hb-F
Incompatible with life.
Microcytic, hemolytic anemia in newborns. -thal trait in adults.
May occur in other forms, ; A; A; 0
Asymptomatic, May occur in G-only or A-only varieties.
Various syndromes. Severity depends on  &  chain imbalances.
Silent carrier. Hb Bart’s () = 1-2% at birth; Hb-H (4) = rare
-thal trait. Hb-Bart’s (4)= 5-10% at birth. Hb-H = rare. SE Asian
-thal trait. Hb-Bart’s (4)= 5-10% at birth. Hb-H = rare. Africans
Hb-H disease. Hb-H (4) in adults = 5-30%. Red cell inclusions.
Hydrops fetalis. Hb-Bart’s = 80-95%; Hb-Portland (22)= 5-20%
Hb-Bart’s ~15% in infants and ~5% in adults.
Clinically and hematologically normal. 1% Hb-CS (longer proteins)
Clinically Hb-H disease
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11
Hemoglobinopthies
Hemoglobin
variant
Hb-S
Genetic defect
Ethnic group
Homozygous or
Heterozygous
Heterozygous/Trait
Homozygous/Disease
10% of American blacks. Clinically asymptomatic. A= 60; S = 33-40
0.2% of American blacks. Moderate to severe disease.
Clinical features/Comments
-6 Glu--Val
African & American blacks
-6 Glu--Val; -121 Glu--Gln
American blacks
Double heterozygous
(rare)
Moderate to severe hemolytic anemia & vasoocclusive complications.
Sickled cells on smear. Neg sickle prep. Hb-S = 50%; Hb-D = 50%
-6 Glu--Val; -6 Glu--Lys
African & American blacks
Double Heterozygous
(0.13%)
Mild chronic hemolytic anemia. Clinical course quite variable, from
completely asymptomatic to severe. Hb-S = 50%; Hb-C = 50%
Prominent target but rare SS-cells. Hb = 10-12 g/l. MCV = 70-90
-6 Glu--Val; -121 Glu--Lys
African & American blacks
Double Heterozygous
Relatively severe chronic hemolytic anemia with vaso-occlusive
episodes.
-6 Glu--Val & -73 Asp--Asn American Blacks
Heterozygous
Double hetero with S
Asymptomatic
Resembles SS-disease
Hb-C
-6 Glu--Lys
African & American blacks
Heterozygous/Trait
Homozygous/Disease
Clinically and hematologically normal. 2% American blacks. 60:40
Mild hemolytic disease
Hb-E
-26 Glu--Lys
South East Asia
Heterozygous/Trait
Homozygous
Clinically asymptomatic. Slightly low MCV. Hb-E = 30%
Clinically mild disease/-thal-trait. Low MCV. Hb-E = 99%
Hb-DLA
-121 Glu--Gln
English/Irish; Punjab
Heterozygous/Trait
Homozygous
Clinically & hematologically normal.
Clinically not disabling.
Hb-O Arab
-121 Glu--Lys
Arabs. African origin
Heterozygous/Trait
Homozygous/Disease
0.5% in American blacks. Hematologically and clinically normal.
Hypochromia and microcytosis.
Hb-GPhila
-68 Asn--Lys
African & American blacks
Hb-SDLA
Hb-SC
Hb-SO Arab
Hb-CHarlem
Can occur with -thal with levels of Hb-G from 33-50%
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12
The contents & pictures in this handout are derived from various sources including books, journal articles and patient material for teaching purposes only. No commercial incentives
are sought or intended.