1. Hemolysis: Hemolysis is the destruction of formed elements. To define more specifically, it is the process, which involves the breakdown of red blood cells (RBCs) and liberation of hemoglobin.

2. Fragility: Susceptibility (to be affected) of RBC to hemolysis or tendency to break easily is called fragility (Fragile = easily broken).

Fragility is of two types:

i. Osmotic fragility, which occurs due to exposure to hypotonic saline

ii. Mechanical fragility, which occurs due to mechanical trauma (wound or injury).

Under normal conditions, only old RBCs are destroyed in the reticuloendothelial system. Abnormal hemolys is is the process by which even younger RBCs are destroyed in large number by the presence of hemolytic agents or hemolysins.


Normally, plasma and RBCs are in osmotic equilibrium. When the osmotic equilibrium is disturbed, the cells are affected. For example, when the RBCs are immersed in hypotonic saline the cells swell and rupture by bursting because of endosmosis. The hemoglobin is released from the ruptured RBCs.


Fragility test is a test that measures the resistance of erythrocytes in hypotonic saline solution. It is done by using sodium chloride solution at different concentrations from 1.2% to 0.2%. The solutions at different concentrations are taken in series of Cohn’s tubes. Then one drop of blood to be tested is added to each tube. The sodium chloride solution and the blood in each tube are mixed well and left undisturbed for some time. Results can be analyzed by observing the tubes directly or by centrifuging the tubes after 15 minutes.

Direct observations

1. If there is no hemolysis: Fluid in the tube appears turbid

2. If hemolysis is started: Turbidity is reduced

3. If hemolysis is completed: Fluid becomes clear.

Observations after centrifugation

1. If there is no hemolysis: Cells sediment at the bottom with clear colorless fluid above

2. If hemolysis is started: Cell sedimentation is less and the fluid becomes slightly reddish because of

the release of small amount of hemoglobin from few hemolyzed RBCs

3. If hemolysis is completed: Fluid becomes more reddish without any sedimentation due to release ofmore amount of hemoglobin from all the hemolyzed cells.

Index for Fragility

After 20 minutes:

No hemolysis = up to 0.6%

Onset of hemolysis = around 0.45%

Completion of hemolysis = around 0.35%

At 0.45%, only the older cells are destroyed because, their membrane is fragile. So, these cells

cannot withstand this hypotonicity. But, younger cells are not affected. At 0.35%, even the younger cells are destroyed.


1. Hemolytic jaundice

2. Antigenantibody reactions

3. Poisoning by chemicals or toxins

4. While using artificial kidney for hemodialysis or heartlung machine during cardiac surgery (rare



Hemolysins or hemolytic agents are the substances, which cause destruction of RBCs. The hemolysins are of two types:

A. Chemical substances

B. Substances of bacterial origin or substances found in body.


1. Alcohol

2. Benzene

3. Chloroform

4. Ether

5. Acids

6. Alkalis

7. Bile salts

8. Saponin

9. Chemical poisons like:

i. Arsenial preparations

ii. Carbolic acid

iii. Nitrobenzene

iv. Resin.



1. Toxic substances or toxins from bacteria:

i. Streptococcus

ii. Staphylococcus

iii. Tetanus bacillus, etc.

2. Venom of poisonous snakes like cobra

3. Hemolysins from normal tissues

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