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1

Hematocrit

Hct: is also called packed cell volume or PCV.
Percentage of RBC in whole blood
Red band - heparin
Blue band no anti ..use for EDTA blood
• Micro hematocrit is the volume of RBCs after centrifuging of whole blood for 5 min at 12,000 rpm.
• Comprises RBCs that are normally 40-50% of blood volume
• Requires a small volume of blood
• Reported in L/L (SI units)

2

Specimen Hematocrit

• Purple (lavender top EDTA ) Venous blood
• or capillary blood collected directly into heparinized capillary tubes - only fill 3/4 of the tube
• Specimens should be centrifuged within 4 hours of collection.
• Hemolyzed samples cannot be used for testing (if the red cells are hemo lyzed we will have less RBC because theyll be ruptured)

3

Normal Values Hematocrit

infant 0.50 - 0.60
toddler ~ 0.35-0.42
male 0.40 - 0.50
female 0.35 - 0.50

4


Critical Values:
Manual Measurement

<0.20 and > 0.60

(SPUN or MICRO HEMATOCRIT)

5

Reading the Hematocrit Value

Hct = height (volume) of RBCs compared to the height (total volume of blood

6

Rule of Three

Hemoglobin X 3= Hematocrit +/-3

Hb 120 x0.03 = 360 g/L
360/1000
Hct 0.36 L/L (+/-0.03)
Note: do not include the buffy coat in the hematocrit reading as this falsely elevate the results

7

Automated (Electronic) Hct Measurement (CALCULATED HEMATOCRIT

---provide an indirect measurement of hematocrit
--- number of RBCs and mean cell volume (MCV-fL) are measured

--- Hct is calculated using formula:
Hct = RBC X MCV
#cells X mean cell volume

MCHC, mean cell haemoglobin concentration (mmol/L) =Hb/Hct
MCHC (g/L) is the average concentration of Hb in the each RBC

8

trapped plasma.

• When the microhematocrit is spun a small amount of plasma remains in the red blood cell portion

• Comparison of spun microhematocrit results with hematocrit results obtained from an electronic cell counter, the spun hematocrit results are generally 1.% to 3% higher due to this trapped plasma

9

RBC with normal Hb - is like what

Cell is normochromic (normal size and normal color)
Hb/Hct ~ 350
MCHC is normal

10

RBC of same volume but less Hb - is like what

Cell is hypochromic (pale)
Hb /Hct < 300
MCHC is low

11

Quality control for hematocrit machine

 Perform test in duplicate; results should be within ±0.01(± 2%)
 run commercially prepared controls on automated instrument
 check centrifuge speed and timer
 proper collection of blood sample (uniform distribution, no hemolysis, no microclots)
 Commercially prepared controls are available for spun hematocrit

12

Sources of Error for hematocrit

• Improper sealing of the capillary tube- ↓ due to loss of RBC’s – the blood comes out of the tube and into the centrifuge
• Increase concentration of anticoagulant – ↓ due to underfilled tube- the ratio of blood to anticoagulant is not proper
• Improper mixing of blood-↓ or ↑
• Time and speed of centrifuge- ↑ due to trapped plasma
• Improper collection of specimen- ↑or ↓
• Hemolysis -↓lysing of RBC’s
• Delay in reading- ↑due to unpacking of RBC’s – if you don’t read right after centrifuge they will start to unpack
• Abnormal RBC morphology due to trapped plasma – fragmented, sickle cell will trap in the plasma
• Buffy coat included-↑

13

Clinical Significance Hematocrit

Clinical Significance Hematocrit is a measurement of the fractional volume of red blood cells.

14

Increased hematocrit

•• Increase dehydration-↓ plasma volume and falsely ↑the hematocrit reading. Lots of RBC but less plasma
• EPO stimulation-increased – drug given to patient with cancer that cant produce RBC. Made in the liver
• residence at high altitude-increased. Lungs produce more hemo so RBC can carry more oxygen – higher hematocrit –more RBC
• Diuretic therapy – release of water so less plasma volume more RBC
• burns – no more plasma so increase of RBC
• an increase in red blood cells, such as in cardiovascular and renal disorders, polycythemia vera, and impaired ventilation

15

Decreased hematocrit

• Bleeding-decreased
• Overhydration, which increases the plasma volume,
• problems with RBC production (sickle cell, amemias, thalasemisa, spherocytosis, bleeding)-decreased
• macrocytic anemias, spherocytosis, thalassemia, hypochromic anemias, and sickle cell anemia-increased trapped plasma

16

Lab Safety for hematocrit

Standard Precautions
Safe use of centrifuge
Use plastic capillaries

17

Buffy Coat Prep

EDTA blood is centrifuged in a Wintrobe tube or lavender top EDTA blood tube
-WBCs are concentrated between the plasma and RBCs
-Buffy Coat is removed by using a long tipped pasture pipette
-Make 2 smears
- Stain with Wright’s
-Used for differential when WBC is low (under 3.0x 109/L)