Packed Cell Volume of Whole Blood
• Hematocrit is defined as the volume occupied by
erythrocytes in a given volume of blood and is usually
expressed as a percentage of the volume of the whole
blood sample.
• The hematocrit may also be referred to as Packed Cell
Volume (PCV).
 Principle:
• The hematocrit is usually determined by spinning a
blood-filled capillary tube in a centrifuge.
 Specimen:
• Venous blood anticoagulated with EDTA or capillary
blood collected directly into heparinized capillary
tubes can be used. Specimens should be centrifuged
within 6 hours of collection.
• Hemolyzed samples cannot be used for testing.
 Reagents and equipment:
• Capillary tubes, heparinized for finger sticks (red tip)
or plain for anticoagulated blood (blue tip)
• Clay-type tube sealant
• Microhematocrit centrifuge
• Microhematocrit reader
• Kimwipes or gauze
 Procedure:
1. Fill two capillary tubes approximately three quarters
full with blood anti-coagulated with EDTA or
heparin. Alternatively, blood for heparinized
capillary tubes may be collected by capillary
puncture. Wipe any excess blood from the outside
of the tube.
2. Seal the end of the tube with the colored ring with
nonabsorbent clay
3.
4.
5.
6.
Balance the tubes in the centrifuge with the clay ends facing
the outside away from the center, touching the rubber
gasket.
Tighten the head cover on the centrifuge and close the top.
Activate the centrifuge for 5 minutes between 10,000 and
15,000 rpm (see comments). Do not use the brake to stop
the centrifuge.
Determine the HCT by using a microhematocrit reading
device Read the level of RBC packing; do not include the
buffy coat (leukocytes and platelets when reading.
The values of the two Hcts should agree within 2% (0.02).
Hematocrite Reader
Reference ranges:
•Newborn
•Infant/child
•Adult male
•Adult female
53-65%
30-43%
42-52%
37-47%
Sources of error and comments
1. Improper sealing of the capillary tube causes a
decreased Hct reading as a result of loss of blood
during centrifugation. a higher number of erythrocytes
are lost in relation to the plasma.
2. An increased amount of anti-coagulant decreases the
Hct reading as a result of erythrocyte shrinking.
3. A decreased or increased result may occur if the
specimen was not properly mixed.
4. The time and speed of the centrifugation and the time
when the results are read are very important.
Insufficient centrifugation. Time for complete packing
should be determined for each centrifuge and
rechecked at regular intervals.
5. The microhematocrit centrifuge should never be
forced to stop by applying pressure to the metal cover
plate. This will cause the RBC layer to “sling”
forward and results in a falsely elevated value.
6. If too much time elapses between when the centrifuge
stops and the capillary tube is removed, the red cells
can begin to settle out and cause a false reading of the
hematocrit.
7.
The buffy coat of the specimen should not be included in the
Hct reading, because its inclusion falsely elevates the result.
8. A decrease or increase in the readings may be seen if the
microhematocrit reader is not used properly.
9. A number of disorders such as:
 Sickle cell anemia
 Macrocytic anemia's
 Hypochromic anemia's
 Spherocytosis
 Thalassemia
may cause plasma to be trapped in the erythrocytes even if the
procedure was performed properly.
9. The trapping of the plasma causes the microhematocrit
to be 1-3% (0.01-0.03 L/L) higher than that obtained
on automated instruments, which calculate the Hct and
are unaffected the trapped plasma.
10. A temporarily low Hct reading may result immediately
after a blood loss, because plasma is replaced faster
than erythrocytes.
11. Proper specimen collection is an important
consideration. The introduction if interstitial fluid
from a skin puncture or the improper flushing of a
catheter causes decreased Hct readings.
• are measurements that describe the size and
oxygencarrying protein (hemoglobin) content of red
blood cells. The indices are used to help in the
differential diagnosis of anemia.
• The relationships between the hematocrit, the
hemoglobin level, and the RBC are converted to red
blood cell indices through mathematical formulas.
• The indices include these measurements: mean
corpuscular volume (MCV); mean corpuscular
hemoglobin (MCH); and mean corpuscular
hemoglobin concentration (MCHC).
Mean Corpuscular Volume
• The MCV is the average volume of the RBC in femtoliters
(fL), or 1015L:
 MCV = Hct (%) X 10 / RBC count (10-12/L).
• Example: Hct = 45%, RBC count = 5.0x1012/L; therefore,
• MCV = 45.0x10 / 5.0 = 90fL
• Cells of normal size (MCV is 80-100fL) are called
normocytic, smaller cells are microcytic, and larger cells are
macrocytic.
 Microcytic cells are found in:
 Patients with iron deficiency anemia.
 Thalassemia.
 Macrocytic cells are found in:
 Patients with liver disease or hypothyroidism
 When there is asynchrony in RBC maturation (termed
megaloblastic anemia's).
 Folate and vitamin B12 deficiencies.
Mean Corpuscular Hemoglobin
(MCH)
• The MCH is the average weight of Hb in an RBC, expressed
in the units of picograms (pg), or 10-12g:
 MCH = Hb (g/dL) X 10 / RBC count (1012/L).
• The reference range for adults is 28-32pg.
• The MCH is not generally considered in the
classification of anemia's.
 Example:
– Hb=16.0 g/fl.
– RBC count=5.0x1012/l.
– MCH=16.0x10 / 5.0 = 32.0pg
Mean Corpuscular Hemoglobin
Concentration (MCHC)
• The MCHC is the average concentration of Hb in
each individual erythrocyte. The
• units used are gram per deciliter (formerly referred to
as a percentage).
 MCHC = Hb (g/dL) X 100 / Hct (%).
• Example: Hb =16 g /dl, Hct = 48%;
• MCHC=16 X 100 / 48 = 33.3g/dL
• Values of normochromic cells range from 32 to
37g/dL.
• Hypochromic cells are less than 32g/dL, and those of
hyperchromic cells are greater than 37g/dL.
• Hypochromic erythrocytes occur in thalassemia and
iron deficiency.
• Because there is a physical limit to the amount of
hemoglobin that can fit in a cell, there is no
hyperchromic category, a cell does not really contain
more than 37g/dL of Hb, but its shape may have
become spherocytic, making the cell appear full.