Microhematocrit and Red Blood Cell Indices by nzoRiV

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									  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.   Balance the tubes in the centrifuge with the clay ends facing
     the outside away from the center, touching the rubber
     gasket.
4.   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.
5.   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.
6.   The values of the two Hcts should agree within 2% (0.02).
                   Hematocrite Reader



Reference ranges:

   •Newborn             53-65%
   •Infant/child        30-43%
   •Adult male          42-52%
   •Adult female        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.
                   The rule of three
• When specimens are analyzed, by either automated or manual
  methods, a quick visual check of the results of Hb and Hct can be
  done by applying the “rule of three.” This rule applies only to
  specimens that have normal erythrocytes.
• The value of the Hct should be three times the value of the Hb ±3.

 Example:
• The following results are obtained from a patient:
   – Hb = 12.0g/dL         Hb (12)x3=36; Hct=0.36L/L
   – Hct = 0.36L/L
   – Acceptable range for the Hct would be 0.33-0.39L/L
• are measurements that describe the size and oxygen
  carrying 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.

								
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