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Haematocrit or PCV

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hematocrit are packed cell volume

determination

hematocrit literally means blood

separation it measures the percentage of

volume of packed red cells in a volume

of whole blood so it is also known as

packed cell volume or PCV it is a

screening test for anemia or

polycythemia

a volume of anticoagulated blood is

placed in a glass tube which is

centrifuge so the blood will be

separated into three layers red cells

Buffy coat of WBC's and platelets and

plasma idly there should be complete

separation of the three layers

hematocrit is a ratio of the height of

red cells column to that of the whole

blood in the tube winthrop tube is a

hundred ten millimeters long narrow

thick walled tube an internal diameter

of 2.5 millimeters it is graduated from

zero to ten centimeters with graduation

both in ascending and descending order

on two sides of the tube the scale with

the markings from zero to ten from above

downwards is used in ESR determination

and from below upward is used for

hematocrit or PCB determination

apparatus required to measure PCV by

winch rope method when drop tube

centrifuge machine pasture Pipit

procedure under aseptic conditions

obtain a venous blood sample carefully

mix the blood sample in EDTA while by

repeated inversion fill the vent drop

tube with the help of pasture pipit to

the 10 centimeters mark there should be

no air bubbles place the winter up tube

in the centrifuge machine and other

winch rope tube filled with water on the

opposite side so as to balance it turn

the centrifuge on to the slow speed and

then gradually increase the speed

centrifuge for 30 minutes at 3,000

revolutions per minute after 30 minutes

stop the centrifuge machine and allow it

to stop by itself

take out the winch rope tube and note

the readings

directly off the graduation the red

cells are seen packed at the bottom and

straw-colored column of plasma is seen

above that in between there is a greyish

white layer consisting of WBC's and

platelets this layer is called the Buffy

coat and is 0.5 to one millimeter in

thickness read the level at which

erythrocytes meet leukocytes quality

control the test should be performed in

duplicate to check for imprecision the

duplicate test should not differ by more

than 50%

sources of error hemolyzed samples may

give falsely decreased results and

should not be used blood must be well

mixed and should be at room temperature

before testing the time and speed of

centrifugation are important factors in

obtaining maximum packing of the red

cells inadequate centrifugation will

result in falsely elevated results due

to excessive trapped plasma the blood to

anticoagulant ratio is particularly

important especially when using EDTA

excessive EDTA will cause a falsely

decreased hematocrit due to shrinkage of

the red blood cells falsely increased

hematocrit s-- may be reported the buffy

coat which is comprised of white cells

and platelets is usually a very thin

whitish layer above the red cells that

can be observed when the blood is

centrifuged in disease states where the

white count is excessively elevated

inclusion of the buffy coat can cause a

significant error failure to read the

hematocrit within 10 minutes after the

centrifuge stops will result in three

dispersion of the red cells in the

plasma and a slanting of the red cell

plasma interface causing a falsely

elevated reading even when the

hematocrit is properly centrifuged there

remains a small amount of plasma trapped

in the red cell column when comparing

man will hematocrit s-- from an

automated instrument which does not have

trapped plasma the manual result is

usually about one to two percent higher

normal ranges for PCV in adult males 40

percent to 50 percent and in adult

females 37 percent to 47 percent

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