Haematocrit (Hct) is a measurement of the proportion of red blood cells (RBC) in the blood, expressed as a percentage. The test is essential in diagnosing anemia, polycythemia, and other blood-related disorders. This article explains the procedure for calculating haematocrit values using both manual and automated methods.

Manual Method – The Microhematocrit Technique:

1. Collecting the blood sample: A small amount of blood is drawn from the patient using a capillary tube – a slim, elongated glass or plastic tube. Anticoagulated blood (blood that has undergone treatment to prevent clotting) is preferred for this method.

2. Preparing for centrifugation: Seal one end of the capillary tube using clay or a tube sealer and place it into a microhematocrit centrifuge holder, making sure the sealed end faces outwards.

3. Centrifugation: The microhematocrit centrifuge is used to separate red blood cells from plasma by spinning the tubes at high speeds, typically around 10,000-16,000 RPM, for about 3-5 minutes.

4. Reading haematocrit value: After centrifugation, you’ll notice that the red blood cells are packed at the bottom of the tube while plasma occupies the top portion. Use a microhematocrit reader or a ruler to measure both the total height of fluid in the capillary tube and packed red blood cells. Divide the height of packed RBCs by the total height of fluid in the tube and multiply by 100 to obtain the haematocrit percentage.

Automated Method – The Electronic Cell Counter Technique:

Modern laboratories commonly rely on electronic cell counters like Coulter counters to initialize a complete blood count (CBC). These instruments calculate haematocrit values by measuring the mean corpuscular volume (MCV), red blood cell count (RBC), and other blood components.

Procedure:

1. Blood sample preparation: Collect a blood sample from the patient using an anticoagulant-treated vacutainer or other specialized tubes. This method requires anticoagulated blood to ensure accurate results.

2. Instrumentation: Load the blood sample onto the electronic cell counter following its specific guidelines. The device processes the blood sample by passing it through a microscopic opening, creating a detectable change in electrical impedance as each cell flows through. By analyzing this electrical data, the instrument calculates various blood parameters, including haematocrit percentages.

Conclusion:

Understanding how to calculate haematocrit allows medical professionals to diagnose and manage numerous health conditions effectively. While manual methods such as the microhematocrit technique are more labor-intensive, they can provide accurate results if performed correctly. On the other hand, automated methods like electronic cell counters offer improved precision and efficiency while processing multiple samples simultaneously. Medical professionals must choose the best method based on their available resources and laboratory requirements for accurate and reliable haematocrit measurements.