Step-by-step measurement of Haematocrit using Micro-hematocrit

What is Haematocrit (Packed Cell Volume-PCV)?

Haematocrit (also called Packed Cell Volume) is the percentage of the volume of blood occupied by red cells. It is a screening test for anemia or polycythemia. When accurate measurements of hemoglobin and red cell counts are available, the absolute values for red cells can be calculated

Haematocrit is comes from the English prefix hemato- and the Greek word krites. Thus, Hematocrit measures the volume of packed red blood cells (RBCs) in relation to whole blood cells. Therefore, it is also known and reported as a packed cell volume.

A glass tube and a centrifuge machine are used to measure hematocrit. After centrifugation, the blood component separates into 3 distinct parts the bottom layer of RBCs, a middle layer of WBCs and platelets, and a top layer of plasma. This method of determining hematocrit using a Wintrobe hematocrit tube is known as the macrohematocrit method (see Image. Wintrobe Hematocrit Tube Containing Blood Components After Centrifugation)

The haematocrit increases when the number of red blood cells increases or when the blood volume is reduced, as in dehydration.

The value can fall to less than normal, showing:

• Anaemia,
• When the body decreases its production of red blood cells
• Increases its destruction of red blood cells.

How haematocrit is important

This test is used to evaluate:

• Anaemia (decrease of red blood cells)
• Blood transfusion decision,
• The effectiveness of those transfusions.
• Polycythaemia (increase in red blood cells)
• Dehydration

The haematocrit is normally needed as a part of the Complete blood count (FBC). It is also repeated at regular intervals for many conditions, including:

• Management of anaemia
• Management from dehydration
• Monitoring of ongoing bleeding to check its severity, and
• Monitoring of polycythaemia.
• The treatment of anaemia

In Manual Haematocrit determination using, Micro-hematocrit method, a volume of anti-coagulated or capillary blood is placed in a glass tube. The glass is then centrifuged so that the blood is separated into its main components: red cells, white cells, platelets and plasma. Ideally there should be complete separation of cells and plasma. Haematocrit is the ratio of the height of the red cell column to that of the whole blood sample in the tube.

Sample Requirements, precautions and test Procedure

Note:

• Blood samples should be as fresh as possible and well mixed.
• Blood specimen handling must be done using proper aseptic precautions, and testing must be immediately after collection.
• Prolonged storage at room temperature can change the shape of RBCs due to metabolism.
• In the microhematocrit method, a smaller blood sample is required, and a single finger-prick sample is enough.
• Proper care must be taken when filling the Wintrobe hematocrit tube. If the tube is reused, it should be thoroughly cleaned, as any foreign particles could interfere with the RBC or plasma column, leading to errors.
• The sealing of the capillary tube must be secure to prevent leakage.
• After approximately 6 hours, the risk of hemolysis rises, leading to erroneous results.
• During centrifugation, whether for macrohematocrit or microhematocrit methods, the centrifuge machine must not be opened. interrupting the centrifugation process rises the likelihood of erroneous results.
•  The operator should wait until the centrifuge has completely stopped before opening the lid.

For the macrohematocrit method, venous blood is obtained as a random sample, without special precautions other than aseptic technique. The blood is typically collected in a vacutainer containing EDTA or in a vial or test tube with EDTA if vacutainers are not available.

Blood is collected in a heparin-filled capillary tube; if anticoagulated blood is available from other hematologic tests, a capillary tube without heparin can be used.

For hematocrit measurement using an automated hematologic cell counter, blood collected with an anticoagulant, such as that used for a complete blood count, is required.

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