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.

Outlines

00:00

🩸 Hematocrit (Packed Cell Volume) Overview

Hematocrit, also known as packed cell volume (PCV), measures the percentage of packed red cells in whole blood. This test is used to screen for conditions like anemia or polycythemia. The process involves centrifuging anticoagulated blood in a glass tube, which separates the blood into three layers: red cells at the bottom, a buffy coat of WBCs and platelets in the middle, and plasma on top. The hematocrit is determined by measuring the ratio of red cells to the total blood volume. A Winthrop tube, with specific dimensions and graduations, is used for this procedure.

05:03

🧪 PCV Determination Using Winthrop Tube

The procedure for measuring PCV involves several steps. First, venous blood is collected and mixed with EDTA to prevent clotting. The Winthrop tube is filled with the blood sample, ensuring no air bubbles are present, and then placed in a centrifuge machine balanced with another tube filled with water. The sample is centrifuged for 30 minutes at 3,000 RPM. After centrifugation, the red cells are packed at the bottom, with plasma on top and a thin buffy coat layer in between. The level where red cells meet leukocytes is used for reading the hematocrit value.

🔬 Quality Control and Sources of Error

Quality control for the hematocrit test involves running the procedure in duplicate, ensuring that the results do not differ by more than 50%. Several factors can cause errors in results, such as hemolyzed samples, improper mixing, or incorrect centrifugation times. An excess of EDTA can shrink red cells, giving falsely low results, while inadequate centrifugation can cause falsely elevated hematocrits due to trapped plasma. The buffy coat, especially in cases of high white cell counts, can also introduce errors if included in the reading.

⚠️ Additional Errors and Considerations in Hematocrit Measurement

Failure to read the hematocrit within 10 minutes after centrifugation can lead to red cell dispersion and slanting of the red cell/plasma interface, causing elevated readings. Even with proper centrifugation, some plasma remains trapped within the red cell column. Manual hematocrit results tend to be 1-2% higher than those obtained using automated instruments due to this trapped plasma. Normal PCV ranges are 40-50% in adult males and 37-47% in adult females.

Keywords

💡Hematocrit

Hematocrit refers to the percentage of red blood cells in a volume of whole blood. This test helps in diagnosing conditions like anemia or polycythemia. In the video, hematocrit is defined as the ratio of the packed red cells to the total blood volume, providing important insights into the health of an individual's blood.

💡Packed Cell Volume (PCV)

Packed Cell Volume (PCV) is another term for hematocrit. It measures the volume of red blood cells in relation to the total blood volume. The video explains that PCV or hematocrit is measured by centrifuging blood, and it plays a crucial role in screening for diseases like anemia.

💡Centrifuge

A centrifuge is a machine used to separate components of blood by spinning the sample at high speeds. In this video, it is highlighted as essential in the process of determining hematocrit by separating blood into three distinct layers: red blood cells, white blood cells and platelets, and plasma.

💡Buffy Coat

The buffy coat is the thin, greyish-white layer between the red blood cells and plasma in a centrifuged blood sample. It consists of white blood cells (WBCs) and platelets. The video points out that the buffy coat's thickness can vary, and its inclusion can lead to measurement errors if not properly accounted for.

💡EDTA

EDTA (Ethylenediaminetetraacetic acid) is an anticoagulant used in blood samples to prevent clotting. The video stresses that correct blood-to-EDTA ratios are vital because excessive EDTA can lead to falsely lowered hematocrit values due to red cell shrinkage.

💡Winthrop Tube

A Winthrop tube is a specialized glass tube used to measure hematocrit. It is graduated and has a narrow diameter, allowing for the precise determination of red blood cell volume. The video explains that the tube's markings are used to read the hematocrit after centrifuging the sample.

💡Plasma

Plasma is the liquid portion of blood, which remains at the top after blood is centrifuged. It is yellowish in color and contains water, electrolytes, and proteins. The video describes how plasma is visually separated from the red blood cells and the buffy coat during the hematocrit test.

💡Polycythemia

Polycythemia is a condition where the body produces too many red blood cells, increasing hematocrit levels. The video uses this term to describe one of the conditions that the hematocrit test can help identify, along with anemia.

💡Error Sources

The video highlights several potential sources of error in the hematocrit test, including hemolyzed samples, incorrect centrifugation time and speed, and issues with blood sample mixing. These errors can lead to inaccurate hematocrit readings, which is critical in diagnosing blood-related health issues.

💡Manual vs. Automated Hematocrit

The video contrasts manual hematocrit measurement with automated instruments. Manual testing may show slightly higher readings due to trapped plasma in red cells, whereas automated machines can give more precise results. This distinction is important for interpreting hematocrit readings accurately.

Highlights

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

Hematocrit is a screening test for anemia or polycythemia.

Blood is separated into three layers after centrifugation: red cells, a buffy coat of WBCs and platelets, and plasma.

The hematocrit is calculated as the ratio of the height of the red cell column to the height of the total blood volume.

A Winthrop tube is used in the PCV determination method, with graduations for both ESR and hematocrit measurements.

The procedure requires mixing blood with EDTA, carefully filling the Winthrop tube to the 10 cm mark, and centrifuging for 30 minutes at 3,000 RPM.

The buffy coat consists of WBCs and platelets and is approximately 0.5-1 mm thick.

Quality control requires duplicate tests, with acceptable differences not exceeding 50%.

Hemolyzed samples or those with excess EDTA can give falsely decreased hematocrit results.

Proper mixing of blood, centrifugation speed and time, and correct blood-to-anticoagulant ratios are critical to avoid errors.

Inadequate centrifugation can trap plasma, leading to falsely elevated results.

Elevated WBC counts may cause errors by enlarging the buffy coat, affecting the hematocrit reading.

Hematocrit results must be read within 10 minutes after centrifugation to prevent red cell dispersion, which can falsely elevate readings.

Manual hematocrit readings are typically 1-2% higher than automated readings due to trapped plasma in the red cell column.

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

Transcripts

[Music]

hematocrit are packed cell volume

determination

hematocrit literally means blood

separation it measures the percentage of

volume of packed red cells in a volume

of whole blood so it is also known as

packed cell volume or PCV it is a

screening test for anemia or

polycythemia

a volume of anticoagulated blood is

placed in a glass tube which is

centrifuge so the blood will be

separated into three layers red cells

Buffy coat of WBC's and platelets and

plasma idly there should be complete

separation of the three layers

hematocrit is a ratio of the height of

red cells column to that of the whole

blood in the tube winthrop tube is a

hundred ten millimeters long narrow

thick walled tube an internal diameter

of 2.5 millimeters it is graduated from

zero to ten centimeters with graduation

both in ascending and descending order

on two sides of the tube the scale with

the markings from zero to ten from above

downwards is used in ESR determination

and from below upward is used for

hematocrit or PCB determination

apparatus required to measure PCV by

winch rope method when drop tube

centrifuge machine pasture Pipit

procedure under aseptic conditions

obtain a venous blood sample carefully

mix the blood sample in EDTA while by

repeated inversion fill the vent drop

tube with the help of pasture pipit to

the 10 centimeters mark there should be

no air bubbles place the winter up tube

in the centrifuge machine and other

winch rope tube filled with water on the

opposite side so as to balance it turn

the centrifuge on to the slow speed and

then gradually increase the speed

centrifuge for 30 minutes at 3,000

revolutions per minute after 30 minutes

stop the centrifuge machine and allow it

to stop by itself

take out the winch rope tube and note

the readings

directly off the graduation the red

cells are seen packed at the bottom and

straw-colored column of plasma is seen

above that in between there is a greyish

white layer consisting of WBC's and

platelets this layer is called the Buffy

coat and is 0.5 to one millimeter in

thickness read the level at which

erythrocytes meet leukocytes quality

control the test should be performed in

duplicate to check for imprecision the

duplicate test should not differ by more

than 50%

sources of error hemolyzed samples may

give falsely decreased results and

should not be used blood must be well

mixed and should be at room temperature

before testing the time and speed of

centrifugation are important factors in

obtaining maximum packing of the red

cells inadequate centrifugation will

result in falsely elevated results due

to excessive trapped plasma the blood to

anticoagulant ratio is particularly

important especially when using EDTA

excessive EDTA will cause a falsely

decreased hematocrit due to shrinkage of

the red blood cells falsely increased

hematocrit s-- may be reported the buffy

coat which is comprised of white cells

and platelets is usually a very thin

whitish layer above the red cells that

can be observed when the blood is

centrifuged in disease states where the

white count is excessively elevated

inclusion of the buffy coat can cause a

significant error failure to read the

hematocrit within 10 minutes after the

centrifuge stops will result in three

dispersion of the red cells in the

plasma and a slanting of the red cell

plasma interface causing a falsely

elevated reading even when the

hematocrit is properly centrifuged there

remains a small amount of plasma trapped

in the red cell column when comparing

man will hematocrit s-- from an

automated instrument which does not have

trapped plasma the manual result is

usually about one to two percent higher

normal ranges for PCV in adult males 40

percent to 50 percent and in adult

females 37 percent to 47 percent

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