Transcript Platelet count

Platelet count
Objectives
To understand the importance of doing a
platelet count
 To know the methods of performing a platelet
count .
 To perform a platelet count .
 Know the possible sources of error and
precautions to be taken in conducting a platelet
count.
 Know the normal values.
 Know the possible causes of abnormal platelet
counts.
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What is a platelet count?
Why is it done?
Bleeding-petechiae
Functions of platelets
Why is platelet counting difficult?
They are small and difficult to discern.
 Their adhesive character-attach readily to
glassware, particles or debris in the diluting
fluid.
 They clump easily.
 Not evenly distributed in the mixture of blood
and diluting fluid.
 They readily disintegrate in the blood diluted
with fluid making it difficult to distinguish them
from debris.
Therefore unless carefully done ,accurate counting
of platelets becomes impossible.
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Methods
 Haemocytometry
(direct count)
1.Brecher-Cronkite method
2.Rees –Ecker method
 Study of blood smear (indirect
method)
 Automated counting.
Brecher –Cronkite method
Principle:
The diluent contains Ammonium Oxalate.
This completely lyses the red cells.
the platelets are then counted with a phase
–haemocytometer and phase contrast
microscope to enhance the refractileness
of the platelets.(or ordinary microscope)
Advantage:
 Identification is easier.
 The error involved is low
Technique
Platelets as seen on
blood smears
Calculation
Sources of error
Precautions to be taken
Glassware must be scrupulously cleaned .
debris and dust are the main sources of error as
they are easily mistaken for platelets.
 The diluting fluid must be filtered just before use .
to remove particles.
 If venous blood is used the platelets must be
counted within 3 hours.
delay causes disintegration and clumping of
platelets.
 Blood should be rapidly diluted .
this is essential to prevent clumping.
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Precautions to be taken
Blood must be thoroughly mixed with the diluent
by shaking the contents at least for 10 minutes.
inadequate mixing results in clumping of
platelets.
 The charged chamber should be kept for 15
minutes under petri dish.
to prevent evaporation and for the cells to settle
down.
 If other haematologic tests are to be done with
platelet count ,and blood is used from the same
puncture ,take blood for the platelet count first.
 The finger should not be squeezed excessively
to collect blood .
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Conditions affecting number of
platelets in blood
Thrombocytopenia
low platelet count
 Thrombocytosis
high platelet count
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Thrombocytopenia
(low platelet count)
Causes
 Reduced production of platelets
 Increased breakdown of platelets
 Trapping of platelets in the spleen
Thrombocytopenia (low platelet count)
As a result of
 a bone marrow disorder such as leukemia
 an immune system malfunction
 as a reaction to a medication.
Complications may range from none at all to
severe bleeding.
 The greatest risk is when platelet count
falls very low <10,000 per microliter .
internal bleeding may occur despite a lack
of any injury.
Reduced production of
platelets
leukemia
 some types of anemia,
 Viral infections,
 cancers that affect bone marrow,
 chemotherapy drugs
 heavy alcohol consumption
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Increased breakdown of
platelets
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Pregnancy
Idiopathic thrombocytopenic purpura
(ITP),
Other autoimmune diseases, such as lupus
and rheumatoid arthritis,
Septicemia severe bacterial infections,
Thrombotic thrombocytopenic purpura
(TTP), a rare, life-threatening condition TTP can
happen sporadically or as a side effect of some
medications.
Hemolytic uremic syndrome,
Dengue fever
Trapping of platelets in the
spleen
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may harbor too many platelets, causing a
decrease in the number of platelets in
circulation.
Signs and symptoms of a low blood platelet
count may include:
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Easy or excessive bruising
Superficial bleeding into the
skin that appears as a rash
of pinpoint-sized reddishpurple spots (petechiae),
usually on the lower legs
Prolonged bleeding from
cuts
Spontaneous bleeding from
gums or nose
Blood in urine or stools
Unusually heavy menstrual
flows
Profuse bleeding during
surgery
Serious or widespread
bleeding indicates an
emergency and requires
immediate care.
Thrombocytosis
(high platelet levels )
reaction to an infection
 surgery
 certain medications
 Polycythemia vera, in which the bone
marrow produces too many platelets too
quickly.
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Questions
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Why does the platelet count give inaccurate
results unless performed carefully?
What are the different methods of platelet
count?
What is the principle of the Brecher –Cronkite
method?
Why is the reagent filtered before every use?
Why is venous blood preferred to capillary blood
for platelet count?
Why is glassware cleaned thoroughly for platelet
count?
Questions
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Why is the blood rapidly diluted and thoroughly mixed
with the diluting fluid?
Why is the charged chamber covered by a petridish for
15 minutes?
How do you identify platelets under the high power
objective?
What are the sources of error in manual method of
platelet count?
What is the normal platelet count?
What are the properties of platelets?what are their
functions?
What are the causes of thrombocytosis and
thrombocytopenia?
Happy counting!