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ESTIMATION OF PACKED CELL VOLUME (HAEMATOCRIT)

COMPLETE BLOOD COUNT

• Hematocrit is a measure of the proportion of blood volume occupied by red blood cells (RBCs).

Blood and Its Components

• Whole Blood Composition:
    - Total Blood Volume:
      - Plasma:
        - Comprises 55% of total blood volume.
        - Contains:
          - Water
          - Proteins
          - Nutrients & metabolic waste
          - Electrolytes
      - Buffy Coat:
        - Comprises <1% of total blood volume.
        - Contains:
          - White blood cells (WBCs), including neutrophils, eosinophils, basophils, monocytes, lymphocytes
          - Platelets
      - Erythrocytes (RBCs):
        - Comprises 45% of total blood volume.

Red Blood Cells (RBCs)

• Definition:
    - RBCs are also referred to as erythrocytes.

• Characteristics:
    - Most numerous formed elements of blood.
    - Normal RBC count in adults ranges from 4 to 5.5 million/microliter of blood.

• Main Function:
    - Transportation of gases, primarily oxygen (O2) and carbon dioxide (CO2).

Hemoglobin and Oxygen Transport

• Hemoglobin Structure:
    - Composed of two types of chains:
      - Beta chains ( chain 1,  chain 2)
      - Alpha chains (a chain 1, a chain 2)
    - Contains iron (Fe2+) component within heme group.

• Functionality:
    - Oxygen is transported from the lungs to various tissues.
    - Oxygen binds to hemoglobin molecules, facilitating gas exchange.
  
  

Haematocrit (Hct)

• Definition:
    - Haematocrit is the percentage of RBCs in a sample of blood.
    - Also known as Packed Cell Volume (PCV).

• Importance:
    - Used as a screening test for conditions like anemia and polycythemia (elevated RBC count).

• Normal PCV Values:
    - Averagely around 45% in normal adults.

Haematocrit Levels by Gender

• Normal blood haematocrit levels:
    - Females: 37% - 47%
    - Males: 42% - 52%

• Conditions related to Haematocrit Levels:
    - Anemia: Characterized by depressed haematocrit percentage.
    - Polycythemia: Characterized by elevated haematocrit percentage.

Laboratory Procedure for Hematocrit Testing

1. Sample Collection Process:
       - Palpate the middle or ring finger and disinfect the area by wiping with an alcohol swab.
       - Prick the finger when dry and allow a large drop of blood to accumulate.
       - Use a heparinized capillary tube to draw up blood via capillary action.
       - Tilt the test tube (approximately 45 degrees) to enable efficient blood collection.
   
   

2. Preparation of Blood Samples:
       - Seal the end of the test tube where the blood was drawn with a cristaseal.
       - Arrange all collected blood samples in the capillary tubes, ensuring sealed ends are pointing outward and taking note of the groove number.
   
   

3. Centrifugation Process:
       - Spin the microcentrifuge at 5000 rpm for 5 minutes.
       - After centrifugation, blood will separate into three layers.
       - Using a haematocrit reader, measure the total length of blood and the length of the RBC layer.
   
   

Equipment and Specifications

• Capillary Tubes:
    - Used for micro-hematocrit testing:
      - Length: 75 mm
      - Outer Diameter (OD): 1.5 - 1.6 mm
      - Available in - 100 tubes per vial, plain or heparinized.

• Hawksley Micro-Haematocrit Reader:
    - Used for determining hematocrit levels after centrifugation.
    - Typically displays values from 0% to 100% and is used to gauge RBC volume in the blood sample.