Hematocrit Determination

Question 1

• The percentage by volume of packed red blood cells in a given sample of blood after centrifugation.

Answer 1

Hematocrit (Hct) or Packed Cell Volume (PCV)

Question 2

• Packed Cell Volume (PCV) or…

Answer 2

erythrocyte volume fraction (EVF)

Question 3

Objective:
-to pack the RBC using the centrifuge force
-forcing all red cell below and plasma above, by centrifugal force

Answer 3

Hematocrit (Hct) or Packed Cell Volume (PCV)

Question 4

Methods of Hematocrit Determination

Answer 4

• Microhematocrit
• Macrohematocrit (Wintrobe)
• Electronic cell counting

Question 5

Hematocrit determination
Principle :
-When a blood Sample to which an anticoagulant is added is centrifuged, the blood is separated into 3 layers :

Answer 5

RBCs are precipitated in the bottom

Buffy coat: greyish white layer made up of WBCs & platelets

Clear plasma layer above

Question 6

MATERIALS

Answer 6

• 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

Question 7

• Glass or plastic
• Plain (Blue-ringed) or heparin (Red-ringed) coated

Answer 7

(MICRO)HEMATOCRIT TUBE

Question 8

Characteristics of MICROhematocrit tube

Answer 8

75 mm long, 1 mm diameter

Question 9

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.

Answer 9

3/4; 2; blue;

90°

hematocrit centrifuge

10,000 to 15,000g; 5

Question 10

Normal Hct Values:
• Males:
• Females:
• Newborns:

The values of the duplicate hematocrits should agree within______(Rodak)

Answer 10

40-54 %

36-47 %

55-68 %

1% (0.01 L/L)

Question 11

Macro hematocrit methid aka

Answer 11

Wintrobe method

Question 12

Macro hematocrit (Wintrobe Method)
Equipment:
• Wintrobe tube (length and diameter???)
• Centrifuge apparatus
• Suitable anticoagulant (e.g. EDTA)
• Disposable syringe
• Pasteur pipette

Answer 12

10 cm. in length & 2.5 cm in diameter

Question 13

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%.

Answer 13

5 ml

Pasteur pipette; Wintrobe tube; 100

2300 g; 30min

zero

Question 14

Clinical Implications
• PCV is affected by the

Answer 14

shape and number of the RBCs

plasma volume

Question 15

-increase in # of circulating RBCs, or
-decrease in plasma volume

-decrease in RBC or
-increase in plasma volume

Answer 15

High PCV

Low PCV

Question 16

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)

Question 17

Sources of Errors and Comments
1. An increased amount of anticoagulant______ the Hct reading as a result of erythrocyte shrinking.

2. Improper sealing of the capillary tube causes a______ Hct reading as a result of loss of blood during centrifugation.
3. 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)
4. The buffy coat of the specimen should not be included in the Hct reading, because its inclusion falsely______ the result.
5. A decrease or increase in the readings may be seen if the_____ is not used properly.
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.

Answer 17

decreases

decreased

elevated

elevates

microhematocrit reader

Question 18

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.

Answer 18

normocytic normochromic red blood cells