诊断学概念ppt课件

PredictiveValues BobL Larson DVM PhDUniversityofMissouriCommercialAgriculture BeefFocusTeam UseandInterpretationofDiagnosticTests Helptomakeadiagnosis doesnotstandalone JudgeseverityofdiseasePredictsubsequentclinicalcourseofdiseaseEstimatelikelyresponsivenesstotherapyDetermineresponsetotherapy posttherapy MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests DiagnosticTests Mustbetestedagainsta goldstandard Althoughnoperfecttestexists agoldstandardisanaccepted reliabletestPropertiesofdiagnostictestsSensitivity proportionoftruepositivesthattestpositiveHoweffectiveisthetestatidentifyinganimalswiththecondition Specificity proportionoftruenegativesthattestnegativeHoweffectiveisthetestatidentifyinganimalswithoutthecondition MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests DiagnosticTests MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests DiagnosticTests MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests DiagnosticTests MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests DiagnosticTests MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests DiagnosticTests MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests DiagnosticTests MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests DiagnosticTests MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests DiagnosticTests Sensitivity a a c Specificity d b d Falsenegative c a c MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests DiagnosticTests Sensitivity a a c Specificity d b d Falsenegative c a c Falsepositive b b d MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests Diagnostictestsuseanarbitrarycut offtoseparatetwopopulations normalvs abnormal MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests Diagnostictestsuseanarbitrarycut offtoseparatetwopopulations normalvs abnormal MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests Diagnostictestsuseanarbitrarycut offtoseparatetwopopulations normalvs abnormal MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests Diagnostictestsuseanarbitrarycut offtoseparatetwopopulations normalvs abnormal MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests Diagnostictestsuseanarbitrarycut offtoseparatetwopopulations normalvs abnormal MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests Diagnostictestsuseanarbitrarycut offtoseparatetwopopulations normalvs abnormal Wherecut offisplaceddeterminessensitivityandspecificity MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests Diagnostictestsuseanarbitrarycut offtoseparatetwopopulations normalvs abnormal Wherecut offisplaceddeterminessensitivityandspecificity Normal Abnormal FewFalseNegativesHighSensitivity result result MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests Diagnostictestsuseanarbitrarycut offtoseparatetwopopulations normalvs abnormal Wherecut offisplaceddeterminessensitivityandspecificity Normal Abnormal FewFalsePositivesHighSpecificity result result MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests Diagnostictestsuseanarbitrarycut offtoseparatetwopopulations normalvs abnormal Wherecut offisplaceddeterminessensitivityandspecificity Normal Abnormal TradeoffbetweenFalse andFalse result result MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests Diagnostictestsuseanarbitrarycut offtoseparatetwopopulations normalvs abnormal TestwithHighSensitivity Normal Abnormal Anegativeresultallowsyoutorule outwhateveryouaretesting result result SnNout MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests Diagnostictestsuseanarbitrarycut offtoseparatetwopopulations normalvs abnormal TestwithHighSpecificity Normal Abnormal Apositiveresultallowsyoutorule inwhateveryouaretesting result result SpPin MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests DiagnosticTests SensitivityandspecificityareinverselyrelatedSensitivityandspecificityarepropertiesofthediagnostictestandtellusifthetestisvalidTestsensitivityandspecificityhavelittleeffectontheconfidenceaveterinarianhasinanindividualresult MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests Because Myillustrationisnotconsistentwithtruediseasedynamicsinapopulation therealworld MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests Because Myillustrationisnotconsistentwithtruediseasedynamicsinapopulation therealworld MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests PredictiveValueWhatwearereallyinterestedin PredictivevaluestellusifatestisusefulPositivePredictiveValue PPV TheprobabilitythatananimalwithapositivetestresultistrulypositiveNegativePredictiveValue NPV TheprobabilitythatananimalwithanegativetestresultistrulynegativeDependentondiseaseprevalenceandtestsensitivityandspecificity MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests PPVandNPV AssumeatestforbovineJohne sis60 sensitiveand90 specificOnexaminationofa5yearolddairycow withtypicalhistory clinicalsignsandpositiveherd matesWeassume90 ofcowswiththisdescriptionarepositive prevalence 90 MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests PPVandNPV AssumeatestforbovineJohne sis60 sensitiveand90 specificOnexaminationofa5yearolddairycow withtypicalhistory clinicalsignsandpositiveherd matesWeassume90 ofcowswiththisdescriptionarepositive prevalence 90 TestSensitivity 540 900 60 MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests PPVandNPV AssumeatestforbovineJohne sis60 sensitiveand90 specificOnexaminationofa5yearolddairycow withtypicalhistory clinicalsignsandpositiveherd matesWeassume90 ofcowswiththisdescriptionarepositive prevalence 90 TestSensitivity 60 MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests PPVandNPV AssumeatestforbovineJohne sis60 sensitiveand90 specificOnexaminationofa5yearolddairycow withtypicalhistory clinicalsignsandpositiveherd matesWeassume90 ofcowswiththisdescriptionarepositive prevalence 90 TestSensitivity 60 NPV 90 450 20 MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests PPVandNPV AssumeatestforbovineJohne sis60 sensitiveand90 specificOnexaminationofa5yearolddairycow withtypicalhistory clinicalsignsandpositiveherd matesWeassume90 ofcowswiththisdescriptionarepositive prevalence 90 TestSensitivity 60 NPV 90 450 20 TestSpecificity 90 MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests PPVandNPV AssumeatestforbovineJohne sis60 sensitiveand90 specificOnexaminationofa5yearolddairycow withtypicalhistory clinicalsignsandpositiveherd matesWeassume90 ofcowswiththisdescriptionarepositive prevalence 90 PPV 540 550 98 NPV 90 450 20 Withpositivetestweare98 suresheisatruepositive Withnegativetestweare20 suresheisatruenegative MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests PPVandNPV AssumeatestforbovineJohne sis60 sensitiveand90 specificOnexaminationofa5yearoldbeefcow withtypicalhistory clinicalsignsandunknownherdstatusWeassume50 ofcowswiththisdescriptionarepositive prevalence 50 MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests PPVandNPV AssumeatestforbovineJohne sis60 sensitiveand90 specificOnexaminationofa5yearoldbeefcow withtypicalhistory clinicalsignsandunknownherdstatusWeassume50 ofcowswiththisdescriptionarepositive prevalence 50 TestSensitivity 300 500 60 MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests PPVandNPV AssumeatestforbovineJohne sis60 sensitiveand90 specificOnexaminationofa5yearoldbeefcow withtypicalhistory clinicalsignsandunknownherdstatusWeassume50 ofcowswiththisdescriptionarepositive prevalence 50 TestSensitivity 60 MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests PPVandNPV AssumeatestforbovineJohne sis60 sensitiveand90 specificOnexaminationofa5yearoldbeefcow withtypicalhistory clinicalsignsandunknownherdstatusWeassume50 ofcowswiththisdescriptionarepositive prevalence 50 TestSensitivity 60 NPV 450 650 69 MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests PPVandNPV AssumeatestforbovineJohne sis60 sensitiveand90 specificOnexaminationofa5yearoldbeefcow withtypicalhistory clinicalsignsandunknownherdstatusWeassume50 ofcowswiththisdescriptionarepositive prevalence 50 TestSensitivity 60 NPV 450 650 69 TestSpecificity 90 PPV 300 350 86 MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests PPVandNPV AssumeatestforbovineJohne sis60 sensitiveand90 specificOnexaminationofa5yearoldbeefcow withtypicalhistory clinicalsignsandunknownherdstatusWeassume50 ofcowswiththisdescriptionarepositive prevalence 50 PPV 300 350 86 NPV 450 650 69 Withpositivetestweare86 suresheisatruepositive Withnegativetestweare69 suresheisatruenegative MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests PredictiveValueofaDiagnosticTestPPVandNPV PPVandNPVaregreatlyinfluencedbypre testlikelihoodofdiseasePublishedprevalencedataYourclinicalskillsandjudgment MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests PPVandNPV TheimmunohistochemistrytestforpersistentlyinfectedBVDanimalsisverygood 96 sensitiveand99 specificHowever theprevalenceofPIanimalsinthegeneralcalfpopulationislow 0 3 So howdoesaverygoodtestperforminapopulationwithlowprevalence MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests PPVandNPV TheimmunohistochemistrytestforpersistentlyinfectedBVDanimalsisverygood 96 sensitiveand99 specificHowever theprevalenceofPIanimalsinthegeneralcalfpopulationislow 0 3 So howdoesaverygoodtestperforminapopulationwithlowprevalence TestSensitivity 96 TestSpecificity 99 MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests PPVandNPV TheimmunohistochemistrytestforpersistentlyinfectedBVDanimalsisverygood 96 sensitiveand99 specificHowever theprevalenceofPIanimalsinthegeneralcalfpopulationislow 0 3 So howdoesaverygoodtestperforminapopulationwithlowprevalence TestSensitivity 96 NPV 98 703 98 715 99 9 TestSpecificity 99 MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests PPVandNPV TheimmunohistochemistrytestforpersistentlyinfectedBVDanimalsisverygood 96 sensitiveand99 specificHowever theprevalenceofPIanimalsinthegeneralcalfpopulationislow 0 3 So howdoesaverygoodtestperforminapopulationwithlowprevalence TestSensitivity 96 NPV 98 703 98 715 99 9 TestSpecificity 99 PPV 288 1 285 22 MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests PPVandNPV TheimmunohistochemistrytestforpersistentlyinfectedBVDanimalsisverygood 96 sensitiveand99 specificHowever theprevalenceofPIanimalsinthegeneralcalfpopulationislow 0 3 So howdoesaverygoodtestperforminapopulationwithlowprevalence TestSensitivity 96 NPV 98 703 98 715 99 9 TestSpecificity 99 PPV 288 1 285 22 MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests PPVandNPV 100head PPVandNPV EvaluatingacomponentofthephysicalexaminationObservationforpresentofdyspneaAuscultationwithstethoscopeEtc TestSensitivity 95 TestSpecificity 96 PregnancyDeterminationviaRectalPalpationAssumehighsensitivityandspecificity truth Prevalenceis95 PPV 99 8 NPV 50 MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests PPVandNPV TakeHome Asprevalencefalls PPV positivepredictivevalue mustalsofallandNPV negativepredictive valuemustrise regardlessofsensitivityandspecificityofthetest Asprevalenceincreases PPVmustincreaseandNPVmustfall regardlessofthesensitivityandspecificityofthetest Yourclinicaljudgmentoftensetsthepre testprobability prevalence MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests DiagnosticTestingStrategy MustknowwhatyouareaskingRuling outapreliminarydiagnosisRuling inapreliminarydiagnosisScreeningforregulatoryorbiosecurityreasonsDescribingaherdproductionsituation MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests DiagnosticTestingStrategy Mustunderstandpredictivevalueoftestinthepopulationyouaretesting MustknowwhatyouareaskingRuling outapreliminarydiagnosisRuling inapreliminarydiagnosisScreeningforregulatoryorbiosecurityreasonsDescribingaherdproductionsituation MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictests DiagnosticTestingStrategy Maywanttousemorethanonediagnostictest Mustunderstandpredictivevalueoftestinthepopulationyouaretesting MustknowwhatyouareaskingRuling outapreliminarydiagnosisRuling inapreliminarydiagnosisScreeningfo