诊断学概念精品文稿.ppt

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1、诊断学概念第1页，本讲稿共57页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.Infectiou

2、s disease epidemiology3.Interpreting diagnostic tests第2页，本讲稿共57页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 positiveHow effective is

3、 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，本讲稿共57页Diagnostic T

4、estsDisease StatusPresentAbsentTest PositiveTest Negative1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第4页，本讲稿共57页Diagnostic TestsDisease StatusPresentAbsentTest PositiveTrue PositiveTest Negative1.Measurement of disease events2.Infectious disease epi

5、demiology3.Interpreting diagnostic tests第5页，本讲稿共57页Diagnostic TestsDisease StatusPresentAbsentTest PositiveTest NegativeTrue Negative1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第6页，本讲稿共57页Diagnostic TestsDisease StatusPresentAbsentTest PositiveFalse

6、 PositiveTest Negative1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第7页，本讲稿共57页Diagnostic TestsDisease StatusPresentAbsentTest PositiveTest NegativeFalse Negative1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic

7、 tests第8页，本讲稿共57页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 tests第9页，本讲稿共57页Diagnostic TestsDisease StatusPresentAbsentTest Positiveaba+bTest

8、 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，本讲稿共57页Diagnostic TestsDisease StatusPresentAbsentTest Positiveaba+bTest Negativecdc+da+cb+da+b+c+dSensitivity =a/(a+c)Specificity=d/(

9、b+d)False negative=c/(a+c)1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第11页，本讲稿共57页Diagnostic TestsDisease StatusPresentAbsentTest Positiveaba+bTest Negativecdc+da+cb+da+b+c+dSensitivity =a/(a+c)Specificity=d/(b+d)False negative=c/(a+c)False positive

10、=b/(b+d)1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第12页，本讲稿共57页Number of animalsMeasurementDiagnostic tests use an arbitrary cut-off to separate two populations(normal vs.abnormal)Population APopulation B1.Measurement of disease events2.Infectious

11、disease epidemiology3.Interpreting diagnostic tests第13页，本讲稿共57页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 tests第

12、14页，本讲稿共57页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 tests第15页，本讲稿共57页Number of animalsMeasurementDiagnostic te

13、sts use an arbitrary cut-off to separate two populations(normal vs.abnormal)Population APopulation B1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第16页，本讲稿共57页Number of animalsMeasurementDiagnostic tests use an arbitrary cut-off to separate two populat

14、ions(normal vs.abnormal)Population APopulation B1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第17页，本讲稿共57页Diagnostic tests use an arbitrary cut-off to separate two populations(normal vs.abnormal)NumberMeasurementWhere cut-off is placed determines sens

15、itivity and specificity1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第18页，本讲稿共57页Diagnostic tests use an arbitrary cut-off to separate two populations(normal vs.abnormal)NumberMeasurementWhere cut-off is placed determines sensitivity and specificityNo

16、rmalAbnormalFew False NegativesHigh Sensitivity-result+result1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第19页，本讲稿共57页Diagnostic tests use an arbitrary cut-off to separate two populations(normal vs.abnormal)NumberMeasurementWhere cut-off is placed de

17、termines sensitivity and specificityNormalAbnormalFew False PositivesHigh Specificity-result+result1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第20页，本讲稿共57页Diagnostic tests use an arbitrary cut-off to separate two populations(normal vs.abnormal)Numbe

18、rMeasurementWhere cut-off is placed determines sensitivity and specificityNormalAbnormalTrade off between False and False+-result+result1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第21页，本讲稿共57页Diagnostic tests use an arbitrary cut-off to separate two

19、 populations(normal vs.abnormal)NumberMeasurementTest with High SensitivityNormalAbnormalA 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，本讲稿共57页Diagnostic tests us

20、e an arbitrary cut-off to separate two populations(normal vs.abnormal)NumberMeasurementTest 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

21、tests第23页，本讲稿共57页Diagnostic TestsSensitivity and specificity are inversely 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.Measu

22、rement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第24页，本讲稿共57页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 diag

23、nostic tests第25页，本讲稿共57页NumberMeasurementBecause My 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，本讲稿共57页Predictive ValueWhat we are really interested inPred

24、ictive values tell us if a test is usefulPositive 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 sensit

25、ivity and specificity1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第27页，本讲稿共57页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-mat

26、esWe assume 90%of cows with this 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，本讲稿共57页PPV and NPVAssume a test for b

27、ovine 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 Positive54010550Test Negative360904509001001,000Test Sensitivity=540/900=6

28、0%1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第29页，本讲稿共57页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 c

29、ows with this 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，本讲稿共57页PPV and NPVAssume a test for bovine Johnes is

30、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

31、cificity=90/100=90%1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第31页，本讲稿共57页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-mates

32、We 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 tests第32页，本

33、讲稿共57页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 Positive54010550Test Negative360904509

34、001001,000PPV=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，本讲稿共57页PPV and NPVAssume a test for bovine Johnes

35、 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 Negative2004506505005001,000Prevalence is 50%(500/1000=50%)1.Measu

36、rement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第34页，本讲稿共57页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 t

37、his 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，本讲稿共57页PPV and NPVAssume a test for bovine Johnes is 60%sensitive an

38、d 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 Sensitivity=60%NPV=450/650=69%1.Measurement of disea

39、se events2.Infectious disease epidemiology3.Interpreting diagnostic tests第36页，本讲稿共57页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

40、 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 diagnostic tests第37页，本讲稿共57页PPV and NPVAssume a test for bovine Johne

41、s 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 Sensitivity=60%NPV=450/650=69%Te

42、st Specificity=90%PPV=300/350=86%1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第38页，本讲稿共57页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

43、n 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 true positiveWith negative test we are 69%sure she is a true negative1.Measurement

44、of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第39页，本讲稿共57页Predictive Value of a Diagnostic TestPPV and NPVPPV and NPV are greatly influenced by pre-test likelihood of diseasePublished prevalence dataYour clinical skills and judgmentPositive%Negative%PrePostPrePostE

45、xample 190981020Example 2508650691.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第40页，本讲稿共57页PPV and NPVThe immunohistochemistry test for persistently infected BVD animals is very good:96%sensitive and 99%specificHowever,the prevalence of PI animals in

46、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 diagnostic tests第41页，本讲稿共57页PPV and NPVThe immunohistochemistry test for persistently infected BVD animals i

47、s 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 Sensitivity=96%Test Spe

48、cificity=99%1.Measurement of disease events2.Infectious disease epidemiology3.Interpreting diagnostic tests第42页，本讲稿共57页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 popu

49、lation 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 Sensitivity=96%NPV=98,703/98,715=99.9%Test Specificity=99%1.Measurement of disease events2.Infectious disease epidemiology3.

50、Interpreting diagnostic tests第43页，本讲稿共57页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 l