Haematocrit or PCV
Summary
TLDRThe 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
🩸 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.
🧪 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.
Mindmap
Keywords
💡Hematocrit
💡Packed Cell Volume (PCV)
💡Centrifuge
💡Buffy Coat
💡EDTA
💡Winthrop Tube
💡Plasma
💡Polycythemia
💡Error Sources
💡Manual vs. Automated Hematocrit
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
you
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