Haematocrit or PCV

Summary

The video explains the hematocrit test, also known as packed cell volume (PCV), which measures the percentage of red blood cells in a blood sample. It's commonly used to screen for anemia or polycythemia. The procedure involves using a Winthrop tube, centrifuging the blood to separate it into three layers: red cells, a buffy coat (white blood cells and platelets), and plasma. The video also covers potential errors, quality control measures, and normal PCV ranges for males and females. Important factors like centrifugation speed, time, and blood-anticoagulant ratio are highlighted to ensure accurate results.

Takeaways

• 🩸 Hematocrit measures the percentage of packed red blood cells in a volume of whole blood, also known as Packed Cell Volume (PCV).
• 🧬 It serves as a screening test for anemia or polycythemia.
• 🧪 Blood is separated into three layers: red cells, Buffy coat (WBCs and platelets), and plasma through centrifugation.
• 🧬 The Winthrop tube, used for hematocrit measurement, is 110 mm long with an internal diameter of 2.5 mm and is graduated from zero to ten centimeters.
• 🔬 The procedure involves obtaining a venous blood sample, mixing it with EDTA, and filling a tube to the 10 cm mark without air bubbles.
• 🌀 The tube is then centrifuged at 3,000 revolutions per minute for 30 minutes to separate the blood components.
• 📏 The hematocrit reading is the ratio of the height of the red cells column to that of the whole blood in the tube.
• 🔍 Quality control involves performing the test in duplicate to ensure precision.
• ⚠️ Sources of error include hemolyzed samples, improper blood mixing, incorrect temperature, inadequate centrifugation, and incorrect blood to anticoagulant ratio.
• 🔎 The manual hematocrit result is usually about 1-2% higher than that from automated instruments due to trapped plasma.
• 📏 Normal ranges for PCV are 40-50% in adult males and 37-47% in adult females.

Q & A

What does hematocrit measure?

Hematocrit measures the percentage of volume of packed red blood cells (RBCs) in a volume of whole blood. It is also known as packed cell volume (PCV).

What are the three layers formed when blood is centrifuged in the Winthrop tube?

The three layers formed are: red blood cells (RBCs) at the bottom, a Buffy coat consisting of white blood cells (WBCs) and platelets in the middle, and plasma at the top.

What is the purpose of the hematocrit test?

The hematocrit test is a screening tool used to diagnose conditions like anemia or polycythemia by measuring the volume of red blood cells in whole blood.

What apparatus is required for measuring PCV using the Winthrop method?

The apparatus required includes a Winthrop tube, centrifuge machine, Pasteur pipette, and anticoagulated blood.

What precautions should be taken to ensure accurate PCV results?

Precautions include mixing the blood sample properly, ensuring there are no air bubbles in the tube, balancing the centrifuge, and avoiding hemolyzed samples. Proper centrifugation time and speed are also essential.

How does an excessive amount of EDTA in the blood sample affect hematocrit readings?

Excessive EDTA can cause a falsely decreased hematocrit because it leads to shrinkage of red blood cells.

What is the Buffy coat, and why is it important in hematocrit testing?

The Buffy coat is a thin, greyish-white layer made of WBCs and platelets. In diseases where the white blood cell count is elevated, the inclusion of the Buffy coat can cause significant errors in hematocrit readings.

What errors can occur if the hematocrit is not read within 10 minutes after centrifugation?

If not read within 10 minutes, red blood cells can re-disperse into the plasma, causing the red cell-plasma interface to slant, resulting in a falsely elevated hematocrit reading.

Why are manual hematocrit readings often 1-2% higher than those from automated instruments?

Manual hematocrit readings are usually 1-2% higher because a small amount of plasma remains trapped in the red cell column, which is not the case with automated instruments.

What are the normal ranges for hematocrit in adult males and females?

Normal hematocrit ranges are 40-50% for adult males and 37-47% for adult females.