Hct or packed cell volumn

is a microscopic observation of volume of RBC in a sample of whole blood

can be measuure manually

used for evaluating and classifying the various types of anemias according to red cell indices

what is hematocrit

The percentage of   Red Blood cells

in a volume of whole blood

It is important to take the reading at the top of the RBC layer

the buffy coat should not be included in the measurement of red cell volumn

Automatic replace manual methods

Spun microhematocrit Method

and

Automated Hematocrit

What is a spun microhematocrit

method?

• can be done with free-flowing capillary blood from skin puncture or EDTA anigcoagulated venous blood
• small amt of blood needed
• high speed centrifuge 
• short centrifuge time 

What is an

Automated Hematocrit?

• multiparameter instruments used
• computed from individual rbc volumn and the red cell count
• not affected by the trapped plasma left in the RBC column for the manual method

Which value of hematocrit is lower?

Using the

Automatic Instrument

or

Centrifugation Method

Hematocrit value obtained by the

Automated instruments

is slightly lower than the

value

obtained by the

Centrifugation Methods

What  blood specimens do you

use for

Spun microhematocrit

• venous blood anticoagulated with EDTA . With venous blood plain uncoated microhematocrit tubes must be used

or

• freely flowing caillary blood-with this blood microhematocrit tubes coated with heparin are used

What blood specimen do you

use for

Automated Analysis?

• Blood anticoagulated with EDTA

• Anemia
• other RBC volumn Alterations

Packed Cell Volumn of Whole Blood

Hematocrit

Centrifugation Method

How should specimens looked after?

• Specimens should be centrifuged within 6 hours of collecting
• you cant use Hemolyzed specimens for testing

Packed Cell Volume of Whole Blood

Hematocrit

Centrifugation Method

What supplies to you need?

• capillary tubes, either plain or hepain coated
• clay type tube sealant
• microhematocrit centrifuge
• micohematocrit reading device

Hematocrit

Microhematocrit Centrifuge

Procedure?

1. Angicoagulant blood-drawn into 2 microhematocrit tubes by capillary action. Fee fllowing capillary specimens should be collected directly into heparinized capillaary tubes. Tubes filled to about 3/4ths of their length, wipe outside of tube with sutibale wipe
2. Sean end of tubes claylike material by placing the dry end of the tube into the sealant
3. place in centrifuge. Sealed ends point toward the outside of centrifuge 
4. Timer set for 5 min fixed speed, 10,000-15000 rpm
5. Read within 10 min - measure the microhematocrit by adjusting the top of the clay sealant to the 0 mark and reading the top of the red cell column. Do not include Buffy coat
6. Microhematocrit preferable epressed as a decimal fraction such as 0.45 L/L 
7. but in current practice the percentage is most commonly used  

Hematocrit

Microhematocrit Sources of Error

Erroneous results from :

including the buffy coat in reading

hemolysis of the specimen

inadequate mixing

Centrifugation time:

 too short

 speed is too low

this will increase in trapped plasma 1-3% will occur

increased amt of trapped plasma can produce errors in patients with an erythorocyte abnormality, such as sickle cell anemia

If tubes remain in centrufuge for more than 10 min at end the plasma and cells will become slanted resulting in inaccurate readings 

What is the microhematocrit used for? 

Detecting

• Anemia
• polycythemia
• hemodilution
• hemoconcntration

Current lab practices- %

SI System packed cell volumn is preferably expressed as a decimal

Units of liter per liter L/L ARE implied

• Angicoagulated blood samples using EDTA should be centrifuged within 6 hours of collection
• EDTA anticoagulant of choice
• blood must not be clotted, hemolyzed
• clotted blood false high
• hemolyzed false low

Hematocrit Value

and

Hemoglobin Determination

there should be a correlatin between the 2 results

The hemocrit results in percent units should be about 3 times the hemoglobin results  

these tubes are not calibrated so need to be measures by a device