Hematocrit Determination Flashcards
• The percentage by volume of packed red blood cells in a given sample of blood after centrifugation.
Hematocrit (Hct) or Packed Cell Volume (PCV)
• Packed Cell Volume (PCV) or…
erythrocyte volume fraction (EVF)
Objective:
-to pack the RBC using the centrifuge force
-forcing all red cell below and plasma above, by centrifugal force
Hematocrit (Hct) or Packed Cell Volume (PCV)
Methods of Hematocrit Determination
• Microhematocrit
• Macrohematocrit (Wintrobe)
• Electronic cell counting
Hematocrit determination
Principle :
-When a blood Sample to which an anticoagulant is added is centrifuged, the blood is separated into 3 layers :
RBCs are precipitated in the bottom
Buffy coat: greyish white layer made up of WBCs & platelets
Clear plasma layer above
MATERIALS
• Blood sample: EDTA or Finger stick blood sample
• capillary tube
• Microhematocrit centrifuge
• microhematocrit reader
• Clay-type tube sealant
• Gauze
• Alcohol swab
• Lancets for capillary puncture
• Glass or plastic
• Plain (Blue-ringed) or heparin (Red-ringed) coated
(MICRO)HEMATOCRIT TUBE
Characteristics of MICROhematocrit tube
75 mm long, 1 mm diameter
Microhematocrit procedure
Procedure
• Fill blood sample up to____ the length of the tube (use____tubes for each sample, plain____-ringed tube for anticoagulated blood, heparinized____-ringed tube for finger stick).
• Seal one end with sealant of clay at a____ degrees.
Place and balance the hematocrit tubes inside a______ with the clay facing outside away from the center., touching the rubber gasket.
Tighten the head cover on the centrifuge and close the top. Centrifuge tubes at_______ for____ mins.
3/4; 2; blue;
90°
hematocrit centrifuge
10,000 to 15,000g; 5
Normal Hct Values:
• Males:
• Females:
• Newborns:
The values of the duplicate hematocrits should agree within______(Rodak)
40-54 %
36-47 %
55-68 %
1% (0.01 L/L)
Macro hematocrit methid aka
Wintrobe method
Macro hematocrit (Wintrobe Method)
Equipment:
• Wintrobe tube (length and diameter???)
• Centrifuge apparatus
• Suitable anticoagulant (e.g. EDTA)
• Disposable syringe
• Pasteur pipette
10 cm. in length & 2.5 cm in diameter
Macrohematocrit (wintrobe) method
Macro hematocrit (Wintrobe Method)
Procedure :
• Collect____. of blood on EDTA
• Mix the anticoagulated blood sample thoroughly.
• Draw the blood sample in a_____ and introduce the pipette up to the bottom of the_____. Fill the tube from the bottom exactly up to the_____ mark. During filling, tip of the pipette is raised, but should remain under the rising meniscus to avoid foaming.
• Centrifuge the sample at______ for____.
• Take the reading of the length of the column of red cells
• Fill the Wintrobe tube to its upper____ mark exactly.
• Place the tube in one bucket of a centrifuge. Rubber adapters must be fitted into the bucket before they are used otherwise Wintrobe tube will break
• After balancing the opposite bucket, centrifuge the tubes for 30 minutes at 2000 - 3000rpm
• Remove the tubes and carefully place it in the Wintrobe tube stand.
• Measure the height of the RBCs layer in mm. The obtained figure is the packed cell volume and is expressed in percentage.
• The overall accuracy of the Wintrobes method as of the order of *3%.
5 ml
Pasteur pipette; Wintrobe tube; 100
2300 g; 30min
zero
Clinical Implications
• PCV is affected by the
shape and number of the RBCs
plasma volume
-increase in # of circulating RBCs, or
-decrease in plasma volume
-decrease in RBC or
-increase in plasma volume
High PCV
Low PCV
Clinical Implications
Higher than normal hematocrit:
• Abnormal increase in red blood cells
• A disorder (polycythemia vera→ 70% rise in Hct level)
• At higher altitudes (lower oxygen supply in the air)
• hypoxia
• Lung or heart disease
• Dehydration
• Burn (due to loss of plasma)
Sources of Errors and Comments
1. An increased amount of anticoagulant______ the Hct reading as a result of erythrocyte shrinking.
- Improper sealing of the capillary tube causes a______ Hct reading as a result of loss of blood during centrifugation.
- The microhematocrit centrifuge should never be forced to stop by applying pressure to the metal cover plate (RBC layer “slings” forward and results in a falsely_____ value)
- The buffy coat of the specimen should not be included in the Hct reading, because its inclusion falsely______ the result.
- A decrease or increase in the readings may be seen if the_____ is not used properly.
- 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.
decreases
decreased
elevated
elevates
microhematocrit reader
Rule of Three
• Applies only to______
• The value of the hematocrit should be three times the value of the hemoglobin plus or minus 3:
HGB X 3 = HCT +/- (0.03 L/L)
• a value discrepant with this rule may indicate abnormal red blood cells, or it may be the first indication of error.
normocytic normochromic red blood cells
