Flashcards in Lecture 3 Deck (17)
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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)
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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)
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Normal Values Hematocrit
infant 0.50 - 0.60
toddler ~ 0.35-0.42
male 0.40 - 0.50
female 0.35 - 0.50
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Critical Values:
Manual Measurement
<0.20 and > 0.60
(SPUN or MICRO HEMATOCRIT)
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Reading the Hematocrit Value
Hct = height (volume) of RBCs compared to the height (total volume of blood
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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
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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
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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
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RBC with normal Hb - is like what
Cell is normochromic (normal size and normal color)
Hb/Hct ~ 350
MCHC is normal
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RBC of same volume but less Hb - is like what
Cell is hypochromic (pale)
Hb /Hct < 300
MCHC is low
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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
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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-↑
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Clinical Significance Hematocrit
Clinical Significance Hematocrit is a measurement of the fractional volume of red blood cells.
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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
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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
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Lab Safety for hematocrit
Standard Precautions
Safe use of centrifuge
Use plastic capillaries
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