How to calculate hematocrit
Hematocrit, also known as the packed cell volume (PCV), is a blood test that measures the percentage of red blood cells (RBCs) in the blood. It is commonly used to diagnose and monitor various health conditions, such as anemia, polycythemia, and hydration status. In this article, we will discuss the methods to calculate hematocrit and how it can provide essential insights into a patient’s health.
Method 1: Centrifuge Technique
The centrifuge method is considered the gold standard for hematocrit measurement. Here are the steps involved in this method:
1. Collect a blood sample using a capillary tube or an anticoagulated venous blood sample.
2. If using a capillary tube, fill it with blood up to the marked line and seal one end.
3. Place the sample in a microhematocrit centrifuge with the sealed end facing outwards.
4. Turn on the centrifuge and spin the sample at high speed (usually 10,000-15,000 RPM) for 5-10 minutes until all blood components separate.
5. After centrifugation, you will see three distinct layers: plasma on top; buffy coat containing white blood cells (WBCs) and platelets in the middle; and RBCs at the bottom.
6. Measure the height of each layer using a microhematocrit reader or a digital caliper.
7. Calculate hematocrit by dividing the height of RBC layer by total height of all layers, then multiplying by 100.
Height of RBC layer = 40 mm
Total height of all layers = 100 mm
Hematocrit = (40 / 100) × 100 = 40%
Method 2: Automated Hematology Analyzer
Modern hematology analyzers provide a more convenient and accurate way of calculating hematocrit. These machines use various technologies, such as impedance, flow cytometry, or optical detection to quantify RBCs and other blood parameters. Here are the basic steps for this method:
1. Collect a venous blood sample in an anticoagulated blood collection tube.
2. Load the sample onto the analyzer’s sampling port.
3. The analyzer automatically aspirates a small amount of blood for analysis.
4. Within minutes, the machine calculates hematocrit along with other blood parameters.
Factors Affecting Hematocrit Measurement
Several factors may affect hematocrit measurement accuracy:
1. Hemolysis: Rupture of red blood cells during sample collection or analysis can lead to artificially low hematocrit.
2. Inadequate mixing of anticoagulated samples: Unmixed samples may cause unequal distribution of cells, resulting in inaccurate measurement.
3. Dehydration or overhydration: Temporary changes in fluid balance can cause fluctuations in hematocrit levels.
Calculating hematocrit is a crucial clinical parameter that helps healthcare professionals diagnose and monitor various health conditions. Understanding how to accurately measure it using either centrifuge technique or automated hematology analyzer is an essential skill for medical professionals. It is also crucial to consider factors that may affect the measurement accuracy during sample collection and analysis for an accurate interpretation of results.