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Sickle Cell Anemia And Thalassemia - NEET PG Pathology 

Apr 11, 2023


Sickle cell disease and thalassemia are genetic disorders and they are caused by errors in the genes for hemoglobin. These are essential topics under Pathology so feel free to revisit this blog post as many times as necessary. 

Read the following post thoroughly and level up your NEET PG Pathology preparation

  • Hemoglobinopathies - Sickle cell anemia and Thalassemia. 
  • Normal hemoglobin

Adult hemoglobin (HbA) is  95% and above and it is made of α 2 and β 2 chains. HbA2 is Less than 3% and is  made of α 2 and delta 2 chain whereas Fetal hemoglobin (HbF) is made of α 2 and gamma 2 chain.

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1. Sickle Cell Anemia

  • Mutation - Point mutation

Int this the Problem occurs at β 6 subunit. Glutamic acid is changed to valine. When glutamic acid is present - patients have HbA. When changed to valine the HbA changes to sickled hemoglobin (HbS). So, it is a missense point mutation.

At β 6 position, if glutamic acid changes to lysine.

It is called HbC hemoglobin disorder.

Factors of Sickle Cell Anemia 

Amount of HbS and HbA- HbS is directly proportional to Sickling, it means more are the levels of hbs more sickling of the cells will be present.

  • Cell converts to Sickle cell when:
    • Normal O2 levels are low - Hypoxia.
    • Less PH - Acidic environment. 
    • Less water - Dehydration.
  • Dehydration: More sickling. 
  • Hypoxia: More sickling.
  • Less PH: More sickling. 
  • Amount of fetal hemoglobin- Fetal hemoglobin has more affinity to oxygen. So when more oxygen levels are present we will find  less sicking.
  • Sickle-alpha thalassemia- In alpha thalassemia there is no α chain so there is formation of Less hemoglobin. So as there is less hemoglobin so we will find less  sickling of the cells.


  • HbAA - Normal.
  • HbAS - Heterozygous type.
    • Sickle cell trait.
  • HbSS - Homozygous type.
    • Sickle cell anemia. 
  • Sickle cell anemia is autosomal resistance disease. 

Compound Heterozygous 

It Contains both harmful genes  Like HbβS, Here both the genes are harmful. β thal and Sickle cell genes are present. If it contains one normal and one harmful gene then this condition is known as heterozygous.


Regular Normal cells

In the absence of oxygen and less pH  The cells convert to sickle shape . This is a reversible process. When there is enough oxygen and proper PH, the sickle shaped cells are converted to normal again and this condition is known as  called reversible sickling. But When there is repeated reversible sickling it leads to irreversible sickling. These sickle shaped cells are very sticky. They stick to each other and forms a mass. If these get stuck in the narrow blood vessels - results in vaso-occlusive crisis. 

Clinical Features of Sickle Cell Anemia 

  • Pallor
  • Splenomegaly - It is an extravascular hemolysis and the cells are  broken by spleen, Causing splenomegaly.
  • Jaundice - RBCs are broken therefore increases the level of  bilirubin.
  • Vaso-occlusive crisis in different organs
    • Brain - results in stroke.
    • Heart - results in MI.
    • Lungs - results in acute chest syndrome.
    • Bones
      • Vertebra - Fish mouth vertebra. 
      • Femur - Avascular necrosis.
      • Digits - Acute dactylitis.
  • Fish mouth vertebra is seen in:
    • Sickle cell anemia
    • Osteoporosis 
  • Fish mouth valve is seen in - Rheumatic Heart Disease (RHD).

Other Crisis of Sickle Cell Anemia 

  • Aplastic crisis: Associated with parvovirus B19 infection.
  • Hemolytic crisis: Associated with Epstein Bar Virus. In this condition Everything is broken off.
  • Sequestration crisis: All sickle cells are sequestered into the spleenand then these cells Attacks the spleen and damages it. This is Referred as multiple splenic infarcts and it leads to decrease in spleen size which is known as Auto splenectomy. 

Initially the spleen gets enlarged as it is performing more functions.

When a sequestration crisis forms - the spleen gets shrinked.

Leads to auto splenectomy. 

Also Read:

CHRONIC INFLAMMATION: Symptoms, Causes, Diagnosis, and Treatment: Pathology

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Diagnosis of Sickle Cell Anemia 

  • Hemoglobin: Hb levels decrease
  • Reticulated Count: As bone marrow works more the reticulocyte count increases. 
  • Bilirubin: As it is an extravascular hemolysis the breakdown of RBCs increases bilirubin.
  • ESR: Erythrocytes Sedimentation Rate. Normal cells get packed and settle down whereas the Sickle cells do not get packed and are not settled down. Hence, ESR is low.

Sickle-shaped cells

These are also called drepanocytes. It is Only seen in sickle cell anemia. Sickle-shaped cells are seen only in sickle cell anemia but not in sickle cell trait.

a. Sickling Test

It is Done if there are no sickle cells to know if it is sickle cell trait or not.

Sickling test

Take a clean slide and Add a drop of patients blood. Add 2% sodium metabisulfite or sodium dithionite To remove oxygen from the cells. And then Cover the slide with coverslip to prevent the exposure of atmospheric oxygen then seal the coverslip with paraffin wax or nail paint. The cells convert to sickle shape. This test is very primitive. This test  Do NOT differentiate between sickle cell anemia and sickle cell trait.

b. Solubility Test

Sickle cells are sticky and also have less solubility. It is also a primitive test. In this Blood is added into the test tube and then sodium dithionite is added to remove oxygen. Sickle cells form polymers, which makes the test tube turbid  which indicates less solubility.

c. Hemoglobin Electrophoresis

  • It is of 2 types
    • Cellulose acetate electrophoresis - pH 8.4 (alkaline).
    • Citrate electrophoresis - pH 6.2 (acidic).
  • Cellulose acetate electrophoresis
    • Hemoglobin electrophoresis has 2 ends - anode and cathode.
    • Hemoglobin bands are formed.
      • Hemoglobin H
      • Hemoglobin A
      • Hemoglobin F
      • Hemoglobin S
      • Hemoglobin A2
    • Mnemonic: HAFSA2
    • These bands are formed from anode to cathode. Along with hemoglobin S, hemoglobin D can also be seen. To differentiate these the other type citrate electrophoresis is used.
  • Citrate electrophoresis
    • Here the hemoglobin S and D are splitted which are formed in cellulose acetate electrophoresis along With Hemoglobin A2 - C, E, O-Arab.

Note: Hemoglobin A2, C, E, O-Arab are present near the cathode.

Concept - Slide is taken and blood is placed at cathode

  • If hemoglobin moves faster and reaches the anode - HbA (normal).
  • If hemoglobin presents both towards anode and cathode - HbAS (sickle cell trait).
  • If hemoglobin moves slower and stays at cathode - HbS (sickle cell anemia).
  • Even the electrophoresis doesn't show proper results as there are overlaps and no quantity is examined.

d. HPLC: High-Pressure Liquid Chromatography. 

  • Gold standard test for any type of hemoglobin disorders.

HPLC graph

  • Graph shows different peaks for different hemoglobin.
Peak NameRetention time, Min
P1 window0.63-0.85
F window0.98-1.20
P2 window1.24-1.40
P3 window1.40-1.90
A0 window1.90-3.10
A2 window3.30-3.90
D window3.90-4.30
S window4.30-4.70
C window4.90-5.30
  • Peak name and retention time
  • The peaks are formed based on the elution time.

Treatment of Sickle Cell Anemia 

  • As it is a hereditary disorder there is nothing more can be done.
  • Hydroxyurea (to treat hypoxia)
    • Increases the fetal hemoglobin. 
    • Therefore increases oxygen affinity.

2. Thalassemia 

Adult hemoglobin is Made up  of α2 and β2 chains.This means there are 2 alpha chains and 2 beta chains. 4 alpha  genes are present on chromosome 16 and 2 beta   genes present on chromosome 11 which  gives 2 alpha chains and 2 beta  chains respectively . Absence of α gene leads to alpha  thalassemia and absence of β gene leads to  β thalassemia.


  • α thalassemia - There is α gene deletion.
  • β thalassemia - There is β gene mutation.

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A. β Thalassemia 

  • 3 types
    • Thalassemia major - It is always dependent on transfusion. It is also known as Cooley anemia.
    • Thalassemia  intermedia
    • Thalassemia  minor / trait - Heterozygous 


Thalassemia major

Thalassemia intermedia

Thalassemia minor / trait

β chain production 

  • No β chain production.
  • β⁰β⁰
  • Little chains present.
  • One β chain is normal.
  • Others are defective.


  • Pallor
  • Jaundice 
  • Splenomegaly
  • Pallor
  • Jaundice 
  • Splenomegaly



3 to 5 (more severe)

5 to 8

> 8

Iron profile




Hb electrophoresis and HPLC

Increased HbF

Both increased

HbA2 > 3.5%

  • β thalassemia is also an extravascular hemolytic disease. 

β Thalassemia - Genetics 

  • Most of them are promoter region mutation.
  • Splicing mutation can also occur - most common.
    • Splicing - removes introns.
    • Mutation in intervening sequence - IVS1-5 G to C in India.
  • Chain termination mutation.
  • Frameshift mutation: Occurs at +8/9th codon or +41/42 codon.
Only deletion in β thalassemia - 619 base pair deletion. 

a. Pathogenesis of β Thalassemia Major

In this condition the β chains are missing. There are no β chains available for α 2 chains to combine. The α 2 chains to sustain and maintain the valence of 4 - tires 2 possibilities:

It stays alone and forms α 4 tetramers. This leads to ineffective erythropoiesis which  Increases load on bone marrow. This is known as  Erythroid hyperplasia.

It combines with gamma 2 (fetal hemoglobin). This has high affinity for oxygen. Less oxygen is reached to tissues . Stimulates the release of erythropoietin. Increases work load on bone marrow - Erythroid hyperplasia 

  • Therefore, in thalassemia major:
    • HbF increases
    • RBC increases but Hb decreases - Typical in thalassemia patients.
    • Iron levels increase.

As there is erythroid hyperplasia so it requires some energy to work more. It Stimulates the GIT to absorb more Iron so the  Iron levels increases. The patients are kept on blood transfusions. Repeated blood transfusion also increases Iron levels and it leads to  Iron overload. Erythroid hyperplasia increases work on other bones and organs as well . It stimulates erythropoiesis from other bones and organs. This erythropoiesis from other bones leads to Crew Cut Skull. The erythropoiesis from other organs is known as  Extra medullary Hematopoiesis. 

Crew Cut Skull

Crew cut appearance of skull

  • This is also called Hair on End appearance. It is seen in both thalassemia and sickle cell anemia. This is an indication of erythropoiesis in other bones.
Chipmunk facies

Chipmunk facies

  • Maxillary Prominence is present.

Peripheral Smear Finding of β Thalassemia Major

  • It is a type of microcytic hypochromic anemia. In this Nucleated RBCs are present. Target cell or codocyte is also present.
  • Confirmatory test - HPLC.
    • Shows high HbF.

Note: Globin gene sequencing is the best technique.

b. β Thalassemia Minor/Trait

  • Microcytic hypochromic anemia. 
  • Asymptomatic. 
  • The condition is confused with iron deficiency anemia. 
FeatureIron Deficiency Anemia β Thalassemia Minor
Type Microcytic hypochromic anemia Microcytic hypochromic anemia 
RDW (size variance)MoreNormal
Mentzer index: MCV/RBC> 13< 13
HbA2 - confirmatory test<3.5%> 3.5%
\Iron deficiency anemia is associated with dietary changes.

Less Iron in diet - Size of RBC decreases.

More Iron  or sufficient Iron - Size becomes normal.

Thalassemia Is associated with defects in genes.

Also Read:

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Nestroft Test

This test is used as One of the screening tests for β thalassemia. It is the Naked Eye Single Tube RBC Osmotic Fragility test. Thalassemia cells are always tough. No microscope is needed to identify the results. The test is used to test osmotic fragility of RBCs.

Method of Nestroft Test

In this 2 test tubes are taken and then the patient's blood and normal person's blood is added in each 5 ml of 0.35% normal saline to both  making a Hypotonic solution. The hypotonic saline starts entering the RBCs. A white paper with black line is placed behind both the tubes. The RBCs of normal person blood breaks due to hypotonic saline and  the black line is visible whereas Thalassemia cells do not break and the line is not visible.

  • Mnemonic: ThALESSemia
    • A - absent lines
    • LESS - Mentzer index is < 13.

B. α Thalassemia 

In this condition the alpha chains are missing due to α gene deletion.

α Gene Detection


AA/AA - All 4 are present


AA/A- 1 α gene is deleted


AA/- - 2 α genes are deleted 

α thalassemia trait

A-/- - 3 α genes are deleted

  • Formation of β 4 tetramers
  • Shows golf ball inclusions
  • HbH disease

All 4 α genes are deleted (- -/- -)

  • Hb Barts disease
  • Results in intrauterine death.
  • Gamma 4 tetramers are formed
  • Mnemonic: Barbaad fetus 
 α Thalassemia

Golf ball inclusions

  • New methylene blue stain is used. The blue ball-like cells indicate golf ball inclusions.  These are due to β 4 tetramers.It is Seen in 3 alpha  gene deletion thalassemia which is  known as HbH disease.
  • Mnemonic: He is a Boy playing Golf at 3 AM
    • He - HbH
    • Boy - β 4 tetramers
    • Golf - Golf ball inclusions 
    • 3 AM - 3 α gene deletion

Also Read : Amyloidosis: Types, Causes, Symptoms, Diagnosis, Risk Factors, Treatment

And that is it! You have now covered everything you need to know about Sickle cell disease and Thalassemia for your Pathology paper preparation. For more interesting and informative posts like these, download the PrepLadder App keep following our blog. 

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