PCV Test

Manual Packed Cell Volume Test

The packed cell volume ( PCV ) is the amount of packed red blood cells following centrifugation , expressed as percentage of total blood volume . The two methods for determination packed cell volume are  the micromethod and the macromethod . In both methods , a column of blood is centrifuge in a tube of uniform bore , closed at one end. The micromethod is more convenient method in many laboratories as routine method . Therefore this test is used for screening of anaemia.

PCV Test

PCV values are reduced than normal in anaemia , hydration and pregnancy. Increased PCV values are found in when there is a loss of plasma as in severe burns , dehydration and also in polycythemia .

• Principle

In the micromethod ,  anticoagulated blood in a glass capillary tube ( haematocrit  tube ) is centrifuged at high – speed to obtain the constant packing of the red cells at the bottom of the tube . The packed cell volume value is read from the scale of a microhaematocrit reader or manually calculated by dividing the height of the red cell column by the height of the total column of blood .

• Specimen

EDTA anticoagulated venous blood / capillary blood collected directly into heparinized capillary tube

• Requirements

  • Microhaematocrit centrifuge
  • Capillary tubes ( disposable )
  • Sealant – clay
  • Microhaematocrit reader

• Procedure

The microhaematocrit tube is filled by capillary action , either from a free flowing puncture wound or a well-mixed venous sample. The capillary tube should be at least 2/3 but not over 3/ 4 full .

PCV test

There are two types of capillary tubes . The plain capillary tubes that without contain anticoagulant and are to be used with anticoagulated blood . The heparinized capillary tubes that contain heparin as anticoagulant and are to be used with capillary blood obtained directly from skin puncture .

Packed Cell Volume Test

The unfilled end of capillary tube seals with the clay sealant material  .  Then the filled tubes place in the radial grooves of the microhaematocrit centrifuge with the sealed end against the outer rim . The filled capillary  tubes centrifuge for 5 minutes ( RCF 12000 – 15000 *g ).

Immediately after centrifuging , the PCV read using the hand- held microhaematocrit reader. Before read the PCV , check for any leakage around the bottom of the tube .

Packed Cell Volume Test

To read the PCV , align the base of the blood in the column ( above the sealant ) with 0  line and the bottom of the meniscus of the plasma with  100 line . The reading point is the top of the red cell column , just below the buffy coat layer ( consisting WBCs and platelets ) . The value of the PCV is taken directly from the reader .

Packed cell volume Test

• Limitation

  • Using a blood sample containing excess EDTA causes erroneous results .
  • Inadequate mixing of the venous blood sample and clot in blood sample affects to the test result.
  • Storing of the specimen beyond 6 – 8 hours results in falsely increased PCV due to swelling of red blood cells .
  • Haemolyzed blood sample causes falsely low results .
  • When , not cleaning and maintaining the microhaematocrit centrifuge as recommended by the manufacture , It causes the errors of the result .
  • A short duration and low speed of centrifugation may not achieve as complete packing as possible.
  • Evaporation of plasma during centrifugation or when left for a time before being read , may be a source of error .
  • Uneven upper surface of the sealer causes the erroneous results .
  • Trapped leukocytes , platelets and particularly trapped plasma may cause errors .

• Reference range

Children at birth            –    44% – 54 %

Children    2 – 5 years   –   34% – 40 %

Children   6 – 12 years  –  35% – 45 %

Adult men                      –   40% – 54 %

Adult women                 –   36 % – 46 %

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