PCV.pdf

Determination of packed cell volume or Hematocrit value

1. February 8
th
2021
Determination of Packed Cell Volume (PCV) OR
Hematocrit (Hct) Value
University of Diyala/ College of Medicine
Department of Physiology
Physiology Lab
Dr. Asmaa Abbas Ajwad
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2. Outlines
•Introduction
•Objectives of PCV Experiment
•Methods and Procedure
•Observations and Reading PCV Value
•Some Clinical Implications
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3. Introduction
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Bloodconsistsofaliquidplasmaportionandasolid
cellularportion.Thesolidportioniscomprisedof
redbloodcells(RBCs),whitebloodcells(WBCs),
andplatelets.
PCVorHctisdefinedasthevolumeofRBCsper
unitvolumeofthewholeblood.
ThePCVisamathematicalexpressionofthenumber
ofRBCs,orpackedcellvolume,expressedasa
percentageofwholeblood.Forexample,apacked
cellvolumeof45%meansthata100-mLsampleof
bloodcontains45mLofpackedRBCs,whichwould
reflectanacceptablelevelofRBCsforapatientof
anygivenage.

4. Introduction
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Adecreaseinthenumberorsizeofredcellsalso
decreasestheamountofspacetheyoccupy,resulting
inalowerPCV.
Anincreaseinthenumberorsizeofredcells
increasestheamountofspacetheyoccupy,resulting
inahigherPCV.
Measurementofpackedcellvolume(PCV)isthe
mostaccurateandsimplestofalltestsinclinical
hematologyfordetectingthepresenceanddegreeof
anemiaorpolycythemia.Incomparison,hemoglobin
estimationislessaccurate,andRBCscountisfar
lessaccurate.

5. Introduction
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PCVdependsprimarilyonthenumberofRBCs,howeverthe
averagesizeoftheRBCsinfluencesthePCV.Conditionsthatcause
RBCsizetobeincreased(e.g.swellingoftheRBCduetochangein
osmoticpressurerelatedtoelevatedsodiumlevels)mayincreasethe
PCVwhileconditionsthatresultinsmallerthannormalRBCs(e.g.
microcytosisrelatedtoirondeficiencyanemia)decreasethePCV.
Ingeneral,highPCVindicateseitherincreaseinthenumberofRBCs
ordecreaseinplasmavolumeasseenincholera.Onanotherhand,a
lowPCVindicateseitherdecreaseinRBCsnumberorincreasein
plasmavolume.
The normal values of PCV vary according to the age and sex of
the individuals. The normal ranges are:
-Males: 40 %–54 %
-Females: 37 %–47 %
-Newborns: 53-65 %
Critical value of PCV = <15 % or >60 %.

6. Purposes of PCV Experiment
Toknow:whatisPCV,methodsfordetermination
PCVvalue,andclinicalimportanceofPCV.
To determine the volume or the amount of
RBCs in 100 mlof blood.
To assess whether there is a sufficient number
of circulating RBCs to transport the required
amount of oxygen throughout the body.
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7. Principle of PCV
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HematocritisderivedfromGreekwords‘Haima’meaning“blood”
,‘krites’meaning“toseparate”.Together“Hematocrit”means‘to
separateblood’wherebloodcellsandplasmaareseparatedby
centrifugation.
Whenaknownvolumeofbloodiscentrifuged,thecellsbeing
heavier,settledownleavingaclearcolumnofplasmaabove.

8. Methods
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•Requireslessbloodandlesstimetogetthe
valueofPCV(commonlyused).Itisthe
methodthatwearegoingtouseintoday
lab.
Microhematocrit
Method
•AlsoknownasaWintrobemethod.
•Timeconsuming,requireslargeamountof
blood,andhasahigherdegreeofplasma
trapping.
Macrohematocrit
Method
•Automatedhematology Analyzer.
AutomatedMethod

9. Materials and Instruments
1.Microhematocrittube(capillarytube)whichis75mminlengthand1mmin
diameter.Itcontainsheparinandshowsaredringatoneendofthetube.
2.Microhematocritcentrifugedevice.
3.Plasticsealtosealoneendofthecapillarytube.
4.Microhematocritreader.
5.Lancet,Alcohol70%,andCotton.
Microhematocrittube Microhematocritreader Microhematocritcentrifuge
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10. Procedure and Observations
•Cleanyourfingerwith70%alcoholandletitdry.
•Bloodisdrawnintothetubebycapillaryphenomenon.Byholdingthetubeina
horizontalmannerandallow2/3to3/4ofthetubetobefilledwithblood.
•Sealthedryendofthetubebyplasticseal.
•ThesealedtubethenisplacedintheradialgroovesoftheMicrohematocrit
centrifugefor5minat11000R.P.m.
•Balancethetubesinthecentrifugewiththeclayendsfacingtheoutsideaway
fromthecenter(placethetubesoppositeeachotherinthecentrifuge).Lookingat
acentrifugedhematocrittube,youwillseethreedistinctlayers:
-Atallupperlayerofclearplasma-slightlyyellow-colored.Itshouldnotbepink
orredwhichwouldindicatehemolysisofredcellsinthesampleorwithinthe
bodyinhemolyticdiseases.
-Agreyish-white(buffylayer)thinlayer(about1mm)in
thicknessconsistingofplateletsandWBCs.
-AtallbottomlayerofRBCswhichhavebeencloselypacked
together.
•Usingthehematocritreader(ruler),readthePCV(Htc)value.
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11. Reading PCV Value
•ThecapillarytubeshouldbeparalleltograduationandlowerlevelofRBCson
zerolineofthescaleandtheupperlevelofthescaleandtheupperlevelofthe
clearplasmaon100%line).Donotincludethebuffycoat(WBCsandplatelets)
whenreadingPCVvalue.
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Procedure of PCV experiment Reading of PCV value

12. Sources of Errors
•Impropersealingofthecapillarytube.
•Timeandspeedofcentrifugation.
•ThebuffycoatofthespecimenshouldnotbeincludedinthePCV
reading,becauseitsinclusionwouldfalselyelevatetheresult.
•Adecreaseorincreaseinthereadingsmaybeseenifthemicro-
hematocritreaderisnotusedproperly.
•Themicrohematocritcentrifugeshouldneverbeforcedtostopby
applyingpressuretothemetalcoverplate.ThiswillcausetheRBCs
layerto“sling”forwardandresultsinafalselyelevatedvalue.
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13. Some Factors that affectHct(PCV)
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Abnormalities of RBCs morphology will affect Hct.
Raised values of WBC will alter the Hct.
People from high altitude have increased Hct.
Chloramphenicol and Penicillin decrease the value.
Pregnantwomenhavelowvaluesdueto
hemodilution.
Dehydration and hemodilutionwill affect the Hct.
After the hemorrhage values are not reliable.
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14. Clinical Implications
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•HighAltitudeandextremephysicalexerciseor
excitement.
Physiological
•PolycythemiaVera,DehydrationleadingtoHemoconcentratione.g.
diarrhea,burns,andvomiting,Congenitalheartfailure,andSevere
chronicobstructivepulmonarydisease(COPD).
Pathological
PCV increases in polycythemia and this could be either:

15. Clinical Implications
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PCV decreases in :
Anemia.
Hemoglobinopathies.
Cirrhosis.
Hemorrhage.
Bone marrow failure
Renal diseases.
Normal pregnancy.
Autoimmune diseases.
Malignancies like lymphoma, leukemia, multiple
myeloma, and Hodgkin's diseases.

16. Advantages Versus Disadvantages of
Microhematocrit Method
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Advantages Disadvantages
Small sample volume
Relatively fast analysis
Hemolysis detected when result is
read
No dilution needed
Carefulpreparationrequired(sealing
ofcapillaries,etc)
Leakageofsealinggivesfalselylow
results(moreRBCswillbelostthan
plasma).
Inbloodwithabnormallysizedor
shapedRBCs,moreplasmawillbe
trapped,causingahigherpositive
biasofHct.
Clotswillleadtofalsepackingofthe
cells,givingfalselyhighHct.

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