诊断学概念幻灯片.ppt

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1、诊断学概念第1页，共57页，编辑于2022年，星期二Use and Interpretation of Diagnostic TestsHelp to make a diagnosis(does not stand alone)Judge severity of diseasePredict subsequent clinical course of diseaseEstimate likely responsiveness to therapyDetermine response to therapy(post therapy)1.Measurement of disease events2

2、.Infectious disease epidemiology3.Interpreting diagnostic tests第2页，共57页，编辑于2022年，星期二Diagnostic TestsMust be tested against a“gold standard”Although no perfect test exists,a gold standard is an accepted,reliable testProperties of diagnostic testsSensitivity=proportion of true positives that test posi

3、tiveHow effective is the test at identifying animals with the condition?Specificity=proportion of true negatives that test negativeHow effective is the test at identifying animals without the condition?1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第3页

4、，共57页，编辑于2022年，星期二Diagnostic TestsDisease StatusPresentAbsentTest PositiveTest Negative1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第4页，共57页，编辑于2022年，星期二Diagnostic TestsDisease StatusPresentAbsentTest PositiveTrue PositiveTest Negative1.Measurement o

5、f disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第5页，共57页，编辑于2022年，星期二Diagnostic TestsDisease StatusPresentAbsentTest PositiveTest NegativeTrue Negative1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第6页，共57页，编辑于2022年，星期二D

6、iagnostic TestsDisease StatusPresentAbsentTest PositiveFalse PositiveTest Negative1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第7页，共57页，编辑于2022年，星期二Diagnostic TestsDisease StatusPresentAbsentTest PositiveTest NegativeFalse Negative1.Measurement of di

7、sease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第8页，共57页，编辑于2022年，星期二Diagnostic TestsDisease StatusPresentAbsentTest Positiveaba+bTest Negativecdc+da+cb+da+b+c+dSensitivity =a/(a+c)1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic t

8、ests第9页，共57页，编辑于2022年，星期二Diagnostic TestsDisease StatusPresentAbsentTest Positiveaba+bTest Negativecdc+da+cb+da+b+c+dSensitivity =a/(a+c)Specificity=d/(b+d)1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第10页，共57页，编辑于2022年，星期二Diagnostic TestsDisease Sta

9、tusPresentAbsentTest Positiveaba+bTest Negativecdc+da+cb+da+b+c+dSensitivity =a/(a+c)Specificity=d/(b+d)False negative=c/(a+c)1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第11页，共57页，编辑于2022年，星期二Diagnostic TestsDisease StatusPresentAbsentTest Positivea

10、ba+bTest Negativecdc+da+cb+da+b+c+dSensitivity =a/(a+c)Specificity=d/(b+d)False negative=c/(a+c)False positive=b/(b+d)1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第12页，共57页，编辑于2022年，星期二Number of animalsMeasurementDiagnostic tests use an arbitrary cut

11、-off to separate two populations(normal vs.abnormal)Population APopulation B1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第13页，共57页，编辑于2022年，星期二Number of animalsMeasurementDiagnostic tests use an arbitrary cut-off to separate two populations(normal vs

12、.abnormal)Population APopulation B1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第14页，共57页，编辑于2022年，星期二Number of animalsMeasurementDiagnostic tests use an arbitrary cut-off to separate two populations(normal vs.abnormal)Population APopulation B1.Measur

13、ement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第15页，共57页，编辑于2022年，星期二Number of animalsMeasurementDiagnostic tests use an arbitrary cut-off to separate two populations(normal vs.abnormal)Population APopulation B1.Measurement of disease events2.Infectious diseas

14、e epidemiology3.Interpreting diagnostic tests第16页，共57页，编辑于2022年，星期二Number of animalsMeasurementDiagnostic tests use an arbitrary cut-off to separate two populations(normal vs.abnormal)Population APopulation B1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic te

15、sts第17页，共57页，编辑于2022年，星期二Diagnostic tests use an arbitrary cut-off to separate two populations(normal vs.abnormal)NumberMeasurementWhere cut-off is placed determines sensitivity and specificity1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第18页，共57页，编辑

16、于2022年，星期二Diagnostic tests use an arbitrary cut-off to separate two populations(normal vs.abnormal)NumberMeasurementWhere cut-off is placed determines sensitivity and specificityNormalAbnormalFew False NegativesHigh Sensitivity-result+result1.Measurement of disease events2.Infectious disease epidemi

17、ology3.Interpreting diagnostic tests第19页，共57页，编辑于2022年，星期二Diagnostic tests use an arbitrary cut-off to separate two populations(normal vs.abnormal)NumberMeasurementWhere cut-off is placed determines sensitivity and specificityNormalAbnormalFew False PositivesHigh Specificity-result+result1.Measureme

18、nt of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第20页，共57页，编辑于2022年，星期二Diagnostic tests use an arbitrary cut-off to separate two populations(normal vs.abnormal)NumberMeasurementWhere cut-off is placed determines sensitivity and specificityNormalAbnormalTrade off be

19、tween False and False+-result+result1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第21页，共57页，编辑于2022年，星期二Diagnostic tests use an arbitrary cut-off to separate two populations(normal vs.abnormal)NumberMeasurementTest with High SensitivityNormalAbnormalA

20、 negative result allows you to rule-out whatever you are testing-result+resultSnNout1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第22页，共57页，编辑于2022年，星期二Diagnostic tests use an arbitrary cut-off to separate two populations(normal vs.abnormal)NumberMeas

21、urementTest with High SpecificityNormalAbnormalA positive result allows you to rule-in whatever you are testing-result+resultSpPin1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第23页，共57页，编辑于2022年，星期二Diagnostic TestsSensitivity and specificity are inver

22、sely relatedSensitivity and specificity are properties of the diagnostic test and tell us if the test is validTest sensitivity and specificity have little effect on the confidence a veterinarian has in an individual result.1.Measurement of disease events2.Infectious disease epidemiology3.Interpretin

23、g diagnostic tests第24页，共57页，编辑于2022年，星期二Because NumberMeasurementMy illustration is not consistent with true disease dynamics in a population(the real world)1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第25页，共57页，编辑于2022年，星期二NumberMeasurementBecause M

24、y illustration is not consistent with true disease dynamics in a population(the real world)1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第26页，共57页，编辑于2022年，星期二Predictive ValueWhat we are really interested inPredictive values tell us if a test is usefu

25、lPositive Predictive Value(PPV)The probability that an animal with a positive test result is truly positiveNegative Predictive Value(NPV)The probability that an animal with a negative test result is truly negativeDependent on disease prevalence and test sensitivity and specificity1.Measurement of di

26、sease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第27页，共57页，编辑于2022年，星期二PPV and NPVAssume a test for bovine Johnes is 60%sensitive and 90%specificOn examination of a 5 year old dairy cow,with typical history,clinical signs and positive herd-matesWe assume 90%of cows with th

27、is description are positive(prevalence=90%)Dz+Dz-Test Positive54010550Test Negative360904509001001,000Prevalence is 90%(900/1000=90%)1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第28页，共57页，编辑于2022年，星期二PPV and NPVAssume a test for bovine Johnes is 60%s

28、ensitive and 90%specificOn examination of a 5 year old dairy cow,with typical history,clinical signs and positive herd-matesWe assume 90%of cows with this description are positive(prevalence=90%)Dz+Dz-Test Positive54010550Test Negative360904509001001,000Test Sensitivity=540/900=60%1.Measurement of d

29、isease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第29页，共57页，编辑于2022年，星期二PPV and NPVAssume a test for bovine Johnes is 60%sensitive and 90%specificOn examination of a 5 year old dairy cow,with typical history,clinical signs and positive herd-matesWe assume 90%of cows with t

30、his description are positive(prevalence=90%)Dz+Dz-Test Positive54010550Test Negative360904509001001,000Test Sensitivity=60%NPV=90/450=20%1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第30页，共57页，编辑于2022年，星期二PPV and NPVAssume a test for bovine Johnes is

31、60%sensitive and 90%specificOn examination of a 5 year old dairy cow,with typical history,clinical signs and positive herd-matesWe assume 90%of cows with this description are positive(prevalence=90%)Dz+Dz-Test Positive54010550Test Negative360904509001001,000Test Sensitivity=60%NPV=90/450=20%Test Spe

32、cificity=90/100=90%1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第31页，共57页，编辑于2022年，星期二PPV and NPVAssume a test for bovine Johnes is 60%sensitive and 90%specificOn examination of a 5 year old dairy cow,with typical history,clinical signs and positive

33、herd-matesWe assume 90%of cows with this description are positive(prevalence=90%)Dz+Dz-Test Positive54010550Test Negative360904509001001,000Test Sensitivity=60%NPV=90/450=20%Test Specificity=90%PPV=540/550=98%1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic t

34、ests第32页，共57页，编辑于2022年，星期二PPV and NPVAssume a test for bovine Johnes is 60%sensitive and 90%specificOn examination of a 5 year old dairy cow,with typical history,clinical signs and positive herd-matesWe assume 90%of cows with this description are positive(prevalence=90%)Dz+Dz-Test Positive54010550Te

35、st Negative360904509001001,000PPV=540/550=98%NPV=90/450=20%With positive test we are 98%sure she is a true positiveWith negative test we are 20%sure she is a true negative1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第33页，共57页，编辑于2022年，星期二PPV and NPVA

36、ssume a test for bovine Johnes is 60%sensitive and 90%specificOn examination of a 5 year old beef cow,with typical history,clinical signs and unknown herd statusWe assume 50%of cows with this description are positive(prevalence=50%)Dz+Dz-Test Positive30050350Test Negative2004506505005001,000Prevalen

37、ce is 50%(500/1000=50%)1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第34页，共57页，编辑于2022年，星期二PPV and NPVAssume a test for bovine Johnes is 60%sensitive and 90%specificOn examination of a 5 year old beef cow,with typical history,clinical signs and unknow

38、n herd statusWe assume 50%of cows with this description are positive(prevalence=50%)Dz+Dz-Test Positive30050350Test Negative2004506505005001,000Test Sensitivity=300/500=60%1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第35页，共57页，编辑于2022年，星期二PPV and NPV

39、Assume a test for bovine Johnes is 60%sensitive and 90%specificOn examination of a 5 year old beef cow,with typical history,clinical signs and unknown herd statusWe assume 50%of cows with this description are positive(prevalence=50%)Dz+Dz-Test Positive30050350Test Negative2004506505005001,000Test Se

40、nsitivity=60%NPV=450/650=69%1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第36页，共57页，编辑于2022年，星期二PPV and NPVAssume a test for bovine Johnes is 60%sensitive and 90%specificOn examination of a 5 year old beef cow,with typical history,clinical signs and u

41、nknown herd statusWe assume 50%of cows with this description are positive(prevalence=50%)Dz+Dz-Test Positive30050350Test Negative2004506505005001,000Test Sensitivity=60%NPV=450/650=69%Test Specificity=450/500=90%1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnosti

42、c tests第37页，共57页，编辑于2022年，星期二PPV and NPVAssume a test for bovine Johnes is 60%sensitive and 90%specificOn examination of a 5 year old beef cow,with typical history,clinical signs and unknown herd statusWe assume 50%of cows with this description are positive(prevalence=50%)Dz+Dz-Test Positive30050350

43、Test Negative2004506505005001,000Test Sensitivity=60%NPV=450/650=69%Test Specificity=90%PPV=300/350=86%1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第38页，共57页，编辑于2022年，星期二PPV and NPVAssume a test for bovine Johnes is 60%sensitive and 90%specificOn exa

44、mination of a 5 year old beef cow,with typical history,clinical signs and unknown herd statusWe assume 50%of cows with this description are positive(prevalence=50%)Dz+Dz-Test Positive30050350Test Negative2004506505005001,000PPV=300/350=86%NPV=450/650=69%With positive test we are 86%sure she is a tru

45、e positiveWith negative test we are 69%sure she is a true negative1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第39页，共57页，编辑于2022年，星期二Predictive Value of a Diagnostic TestPPV and NPVPPV and NPV are greatly influenced by pre-test likelihood of diseaseP

46、ublished prevalence dataYour clinical skills and judgmentPositive%Negative%PrePostPrePostExample 190981020Example 2508650691.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第40页，共57页，编辑于2022年，星期二PPV and NPVThe immunohistochemistry test for persistently in

47、fected BVD animals is very good:96%sensitive and 99%specificHowever,the prevalence of PI animals in the general calf population is low(0.3%)So,how does a very good test perform in a population with low prevalence?1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnost

48、ic tests第41页，共57页，编辑于2022年，星期二PPV and NPVThe immunohistochemistry test for persistently infected BVD animals is very good:96%sensitive and 99%specificHowever,the prevalence of PI animals in the general calf population is low(0.3%)So,how does a very good test perform in a population with low prevalen

49、ce?BVD PIDz+Dz-Test Positive2889971,285Test Negative1298,70398,71530099,700100,000Test Sensitivity=96%Test Specificity=99%1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第42页，共57页，编辑于2022年，星期二PPV and NPVThe immunohistochemistry test for persistently inf

50、ected BVD animals is very good:96%sensitive and 99%specificHowever,the prevalence of PI animals in the general calf population is low(0.3%)So,how does a very good test perform in a population with low prevalence?BVD PIDz+Dz-Test Positive2889971,285Test Negative1298,70398,71530099,700100,000Test Sens