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Overview–Courses.ppt

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Biologicalvariation Introduction Estimation(ANOVAapplication) Index-of-individuality Comparisonofaresultwithareferenceinterval("Grey-zone") Referencechangevalue(RCV) Referenceintervalandbiologicalvariation Referenceintervalencompasses: pre-analyticalimprecision analyticalimprecision within-subjectbiologicalvariation between-subjectbiologicalvariation Usefulnessofreferenceintervals Referenceintervalsareofmostuse whenthebetween-subjectvariationissmallerthanthewithin-subjectvariation: CVB-S<CVW-S,orCVW-S/CVB-S>1 Ifnot,individualsmayhavevalueswhichliewithinreferencelimitsbutarehighlyunusualforthem:Seealsolater:Indexofindividuality Usesofbiologicalvariation Settingdesirableanalyticalgoals Assessingsignificanceofchangesinserialresults Assessingutilityofpopulationbasedreferencevalues Decidingnumberofspecimensrequiredtoassesshomeostaticsetpointofanindividual Determiningoptimummodeforresultreporting Comparingavailabletests Assessingclinicalutilityoftests Abbreviationsforbiologicalvariation CVW-S=Within-subject CVB-S=Between-subject CVG="Group"=SQRT(CV2W-S+CV2B-S)=¼ofthereferenceinterval Note:sometimesCVGisusedtodesignateCVB-S(e.g.intheWestgarddatabaseonanalyticalspecifications)Estimationofbiologicalvariation(ANOVA-application)Analytical&biologicalvariationAnalytical&withinbiologicalvariationIndex-of-individuality(II)Index-of-individuality(II)Comparisonofaresultwithareference-intervalReferenceChangeValue(RCV),orMedicallysignificantdifference(Dmed) 95%intervalfordifferencebetweentwosamplingsandmeasurements Dmed=1.96•[2•(CV2W-S+CV2Anal)]½ TheRCVisparticularimportantforanalyteswithhighCVB-S. medforthe“creatinineclearance” C :mlplasmaclearedperminperstandardbodysurface Ucr :concentrationofcreatinineinurine(mg/ml) Pcr :concentrationofcreatinineinplasma(mg/ml) V :volumeurineflowinmlpermin A :bodysurfaceinm2 For Ucr :1mg/ml Pcr :0.01mg/ml V :1ml/min A :1.88m2(manof70kgand1.75mtall) isC=92ml/min/1.73m2 Calculationofsa: WhenCVa=2%forUcr=1mg/ml,thensa=0.02mg/ml.