DIAGNOSTIC & SCREENING Evidence-based Medicine. Pengalaman/Data Empiric Masalah experience-based...

DIAGNOSTIC & SCREENING

Evidence-based Medicine

Pengalaman/Data EmpiricPengalaman/Data Empiric

Masalah experience-based medicineMasalah experience-based medicine

Nilai-nilai kebenaranNilai-nilai kebenaran Nilai-nilai pembenaranNilai-nilai pembenaran

Appendisitis akutAppendisitis akutAppendisitis akutAppendisitis akut

Appendisitis akutAppendisitis akutAppendisitis akutAppendisitis akutMcBurney sign (+)McBurney sign (+)

McBurney sign (+)McBurney sign (+)

USGUSG 7676 9966CT ScanCT Scan 8383 9933USGUSG 7676 9966CT ScanCT Scan 8383 9933

USGUSG 8787 9988CT Scan CT Scan 9922 100 100USGUSG 8787 9988CT Scan CT Scan 9922 100 100

Use of USG vs. CT Scan in diagnosing acute appendicitisUse of USG vs. CT Scan in diagnosing acute appendicitis

SensitivitySensitivity Specificity Specificity SensitivitySensitivity Specificity Specificity

Negative appendectomy: 20-40%Negative appendectomy: 20-40%Negative appendectomy: 20-40%Negative appendectomy: 20-40%

Styrud et al, , Intl J for Quality in Health Care, 2000Styrud et al, , Intl J for Quality in Health Care, 2000

SensitivitySensitivity Specificity Specificity SensitivitySensitivity Specificity Specificity

PPatientatientOr Or

ProblemProblem

IInterventionntervention CComparisonomparison OOutcomesutcomes

AppendicitAppendicitisis

AppendicitAppendicitisis

CT scanCT scanCT scanCT scan USGUSGUSGUSGMore More

sensitive sensitive & specific& specific

More More sensitive sensitive & specific& specific

Clinical Question

PP II CC OO

Foreground QuestionForeground Question

Natural History of DiseaseNatural History of Disease

AAAA BBBB CCCC DDDD EEEE FFFF

A.A. Biologic onset of the conditionBiologic onset of the conditionB.B. Pathologic evidence of disease detectable by screeningPathologic evidence of disease detectable by screeningC.C. Signs and symptoms of diseaseSigns and symptoms of diseaseD.D. Health care soughtHealth care soughtE.E. Diagnosis of diseaseDiagnosis of diseaseF.F. Treatment of diseaseTreatment of disease

A.A. Biologic onset of the conditionBiologic onset of the conditionB.B. Pathologic evidence of disease detectable by screeningPathologic evidence of disease detectable by screeningC.C. Signs and symptoms of diseaseSigns and symptoms of diseaseD.D. Health care soughtHealth care soughtE.E. Diagnosis of diseaseDiagnosis of diseaseF.F. Treatment of diseaseTreatment of disease

PreclinicalPreclinicalPreclinicalPreclinical ClinicalClinicalClinicalClinical OutcomeOutcomeOutcomeOutcome

Issues in ScreeningIssues in Screening

Improve outcomes of illness Improve outcomes of illness • Improve morbidity: exampleImprove morbidity: example• Improve mortality: exampleImprove mortality: example

Improve outcomes of illness Improve outcomes of illness • Improve morbidity: exampleImprove morbidity: example• Improve mortality: exampleImprove mortality: example

DefinitionDefinitionDefinitionDefinition

Early detection of preclinical Early detection of preclinical disease in asymptomatic personsdisease in asymptomatic personsEarly detection of preclinical Early detection of preclinical disease in asymptomatic personsdisease in asymptomatic persons

Purpose of screeningPurpose of screeningPurpose of screeningPurpose of screening

DEFINITION: Screening

The assessment or evaluation of people, The assessment or evaluation of people, who have no symptoms of disease, in who have no symptoms of disease, in order to classify them as to likelihood of order to classify them as to likelihood of having a particular diseasehaving a particular disease

The assessment or evaluation of people, The assessment or evaluation of people, who have no symptoms of disease, in who have no symptoms of disease, in order to classify them as to likelihood of order to classify them as to likelihood of having a particular diseasehaving a particular disease

Difference Between Diagnostic and Difference Between Diagnostic and Screening TestScreening Test

Difference Between Diagnostic and Difference Between Diagnostic and Screening TestScreening Test

is used to confirm diagnosis is used to confirm diagnosis in a patient who is sickin a patient who is sickis used to confirm diagnosis is used to confirm diagnosis in a patient who is sickin a patient who is sick

is offered to subjects who are is offered to subjects who are free of symptoms or signs of free of symptoms or signs of diseasedisease

is offered to subjects who are is offered to subjects who are free of symptoms or signs of free of symptoms or signs of diseasedisease

Screening testScreening testScreening testScreening test

Diagnostic testingDiagnostic testingDiagnostic testingDiagnostic testing

ObjectivesObjectivesObjectivesObjectives

However, in clinical practice diagnostic results may be in error

However, in clinical practice diagnostic results may be in error

diagnosticdiagnosticdiagnosticdiagnostic screeningscreeningscreeningscreening

detect disease detect disease at all stageat all stage

detect disease detect disease at all stageat all stage

detect early detect early stage of diseasestage of disease

detect early detect early stage of diseasestage of disease

Examples Of Screening TestsExamples Of Screening TestsExamples Of Screening TestsExamples Of Screening Tests• Blood pressureBlood pressure• ScoliosisScoliosis• Vision/GlaucomaVision/Glaucoma• MammographyMammography• Pap smearsPap smears• CholesterolCholesterol• DiabetesDiabetes

• Blood pressureBlood pressure• ScoliosisScoliosis• Vision/GlaucomaVision/Glaucoma• MammographyMammography• Pap smearsPap smears• CholesterolCholesterol• DiabetesDiabetes

• DepressionDepression

• Nutrition Nutrition screeningscreening

• Drug/alcohol useDrug/alcohol use

• LeadLead

• AbuseAbuse

• Fall riskFall risk

• DepressionDepression

• Nutrition Nutrition screeningscreening

• Drug/alcohol useDrug/alcohol use

• LeadLead

• AbuseAbuse

• Fall riskFall risk

WHY WE NEED A WHY WE NEED A GOOD DIAGNOSTIC GOOD DIAGNOSTIC

TESTTEST

WHY WE NEED A WHY WE NEED A GOOD DIAGNOSTIC GOOD DIAGNOSTIC

TESTTEST

Widal agglutination testWidal agglutination test

ThypoiThypoidd

1.1. absence of infection by absence of infection by S typhiS typhi2.2. the carrier statethe carrier state3.3. an inadequate inoculum of bacterial an inadequate inoculum of bacterial

antigen in the host to induce antibody antigen in the host to induce antibody productionproduction

4.4. technical difficulty or errors in the technical difficulty or errors in the performance of the testperformance of the test

5.5. previous antibiotic treatmentprevious antibiotic treatment6.6. variability in the preparation of variability in the preparation of

commercial antigenscommercial antigens

1.1. absence of infection by absence of infection by S typhiS typhi2.2. the carrier statethe carrier state3.3. an inadequate inoculum of bacterial an inadequate inoculum of bacterial

antigen in the host to induce antibody antigen in the host to induce antibody productionproduction

4.4. technical difficulty or errors in the technical difficulty or errors in the performance of the testperformance of the test

5.5. previous antibiotic treatmentprevious antibiotic treatment6.6. variability in the preparation of variability in the preparation of

commercial antigenscommercial antigens

Causes of negative Widal agglutination tests

109 years after its invention (1896 – 2005)109 years after its invention (1896 – 2005)

Postgrad Med J 2000;76:80–84

1.1. the patient being tested has typhoid feverthe patient being tested has typhoid fever2.2. previous immunisation with previous immunisation with Salmonella Salmonella

antigen.antigen.3.3. cross-reaction with non-typhoidal cross-reaction with non-typhoidal SalmonellaSalmonella..4.4. variability and poorly standardised variability and poorly standardised

commercial antigen preparationcommercial antigen preparation5.5. infection with malaria or other infection with malaria or other

enterobacteriaceaeenterobacteriaceae6.6. other diseases such as dengueother diseases such as dengue

1.1. the patient being tested has typhoid feverthe patient being tested has typhoid fever2.2. previous immunisation with previous immunisation with Salmonella Salmonella

antigen.antigen.3.3. cross-reaction with non-typhoidal cross-reaction with non-typhoidal SalmonellaSalmonella..4.4. variability and poorly standardised variability and poorly standardised

commercial antigen preparationcommercial antigen preparation5.5. infection with malaria or other infection with malaria or other

enterobacteriaceaeenterobacteriaceae6.6. other diseases such as dengueother diseases such as dengue

Causes of positive Widal agglutination tests

• Multi-Test Dip-S-Ticks Multi-Test Dip-S-Ticks for Serotype Typhi for Serotype Typhi 89 89 50 50

• TyphiDot TyphiDot 79 79 89 89 • TUBEX TUBEX 78 78 94 94 • Widal testing in Widal testing in

the hospitalthe hospitalb b 64 64 7676• Widal testing at the Widal testing at the

Pasteur Institute Pasteur Institute 61 61 100 100

• Multi-Test Dip-S-Ticks Multi-Test Dip-S-Ticks for Serotype Typhi for Serotype Typhi 89 89 50 50

• TyphiDot TyphiDot 79 79 89 89 • TUBEX TUBEX 78 78 94 94 • Widal testing in Widal testing in

the hospitalthe hospitalb b 64 64 7676• Widal testing at the Widal testing at the

Pasteur Institute Pasteur Institute 61 61 100 100

Diagnostic toolDiagnostic tool Sensitivity Specificity Sensitivity Specificity (%)(%) (%) (%)

Diagnostic toolDiagnostic tool Sensitivity Specificity Sensitivity Specificity (%)(%) (%) (%)

Characteristics of ValidityCharacteristics of ValidityCharacteristics of ValidityCharacteristics of Validity

the ability of a test to determine those who do not have the disease

the ability of a test to correctly identify those who have the disease or condition

SensitivitSensitivityy

SpecificitSpecificityy

test result negatif

test result negatif

No treatment might be

given

No treatment might be

given

Wrong treatment

(medical error)

Wrong treatment

(medical error)

Test result

positive

Test result

positive

Diagnostic/screening

Diagnostic/screening

Misleading

Accurate

Best diagnostic tools

Highly sensitive/specific False positive/negative

PneumoniaPneumonia

NoNoPneumoniaPneumonia

PneumoniaPneumonia

NoNoPneumoniaPneumonia

PneumoniaPneumonia

No No PneumoniaPneumonia

DIAGNOSTIC TEST PROCEDUREDIAGNOSTIC TEST PROCEDURE

GOLD STANDARDGOLD STANDARD

RespiratoryRespiratoryraterate

Disease Disease (+)(+)

No No DiseaseDisease

Gold Standard for DxGold Standard for Dx

Disease(+Disease(+))

No DiseaseNo Disease

TTEESSTT

True True positivepositive

True True negativenegative

False False negativenegative

False False positivepositive

Sensitivity& Specificity Sensitivity& Specificity Sensitivity& Specificity Sensitivity& Specificity

How to calculate these How to calculate these using a 2 X 2 tableusing a 2 X 2 table

How to calculate these How to calculate these using a 2 X 2 tableusing a 2 X 2 table

aa b b

cc d d

Disease Disease (+)(+)

No No DiseaseDisease


Disease(+Disease(+))


TTEESSTT

a + ca + c b + db + d

Sensitivity = a / (a+c) x 100%Sensitivity = a / (a+c) x 100%Sensitivity = a / (a+c) x 100%Sensitivity = a / (a+c) x 100%

Sensitivity is the ability of the test to detect the presence Sensitivity is the ability of the test to detect the presence of diseaseof disease

is the proportion of patients with disease who test positive

Sensitivity = Sensitivity = 90%90%

of those who have anemia, 90% will test of those who have anemia, 90% will test positivepositiveof those who have anemia, 90% will test of those who have anemia, 90% will test positivepositiveIt also means that in those that have It also means that in those that have anemia, 10% will test negative (i.e. there is anemia, 10% will test negative (i.e. there is a 10% false negative rate in those with a 10% false negative rate in those with anemia)anemia)

It also means that in those that have It also means that in those that have anemia, 10% will test negative (i.e. there is anemia, 10% will test negative (i.e. there is a 10% false negative rate in those with a 10% false negative rate in those with anemia)anemia)

Diagnostic test for anemia using ferritinDiagnostic test for anemia using ferritin

anemiaanemia Dx testDx test

Positive = 90%Positive = 90%

Negative = 10%Negative = 10%Negative = 10%Negative = 10%

aa b b

cc d d

Disease (+)Disease (+) No No DiseaseDisease


Disease(+)Disease(+)


TTEESSTT

a + ca + c b + db + d

Specificity = d / (b+d) x 100%Specificity = d / (b+d) x 100%Specificity = d / (b+d) x 100%Specificity = d / (b+d) x 100%

Specificity is the ability of the test to detect the absence Specificity is the ability of the test to detect the absence of diseaseof disease

is the proportion of patients without disease who test negative

Spesificity = 85%Spesificity = 85%

of those who do not have anemia, 85% will test of those who do not have anemia, 85% will test negativenegative

It also means that in those that do not have It also means that in those that do not have anemia, 15% will test positive (i.e. there is a anemia, 15% will test positive (i.e. there is a 15% false positive rate in those without 15% false positive rate in those without anemia)anemia)

Diagnostic test for anemia using ferritinDiagnostic test for anemia using ferritin

Non anemiaNon anemia Dx testDx test

Positive = 15 Positive = 15 %%Positive = 15 Positive = 15 %%

Negative = 85%Negative = 85%

If a defined population of patients is being If a defined population of patients is being evaluated, the pretest probability is equal evaluated, the pretest probability is equal to the prevalence of disease in the to the prevalence of disease in the population. population.

If a defined population of patients is being If a defined population of patients is being evaluated, the pretest probability is equal evaluated, the pretest probability is equal to the prevalence of disease in the to the prevalence of disease in the population. population.

Pretest ProbabilityPretest Probability

• is the estimated likelihood of disease is the estimated likelihood of disease before the test is donebefore the test is done

• = prior probability= prior probability

• is the estimated likelihood of disease is the estimated likelihood of disease before the test is donebefore the test is done

• = prior probability= prior probability

It is the proportion of total patients who It is the proportion of total patients who have the disease. have the disease. It is the proportion of total patients who It is the proportion of total patients who have the disease. have the disease.

Note that ………………………..Note that ………………………..Note that ………………………..Note that ………………………..

Sensitivity is calculated based only Sensitivity is calculated based only on those who have disease, andon those who have disease, andSensitivity is calculated based only Sensitivity is calculated based only on those who have disease, andon those who have disease, and

Therefore, neither sensitivity nor Therefore, neither sensitivity nor specificity are affected by the specificity are affected by the prevalence of the target conditionprevalence of the target condition

specificity is calculated only on those specificity is calculated only on those who do not have diseasewho do not have diseasespecificity is calculated only on those specificity is calculated only on those who do not have diseasewho do not have disease

The trade off between sensitivity and specificity

The trade off between sensitivity and specificity

In most cases as sensitivity increases, specificity decreases, and vice versa (i.e they are inversely related to each other

In most cases as sensitivity increases, specificity decreases, and vice versa (i.e they are inversely related to each other

The Sensitivity/specificity trade offThe Sensitivity/specificity trade off

An example of when you might want An example of when you might want a high sensitivity is a screen for a high sensitivity is a screen for neonatal hypothyroidism (you neonatal hypothyroidism (you wouldnwouldn’’t want many false negatives t want many false negatives which might lead to irreversible which might lead to irreversible cognitive damagecognitive damage

The Sensitivity/specificity trade offThe Sensitivity/specificity trade off

An example of when you might want An example of when you might want a a high specificityhigh specificity is a screen for HIV is a screen for HIV (you wouldn(you wouldn’’t want many false t want many false positives due to the emotional positives due to the emotional trauma)trauma)

(Knapp and Miller, 1992)

““ . . . individuals with the condition who . . . individuals with the condition who are correctly identified as diseased by are correctly identified as diseased by the new testthe new test””

““ . . . individuals with the condition who . . . individuals with the condition who are correctly identified as diseased by are correctly identified as diseased by the new testthe new test””

True positive:True positive:True positive:True positive:

False positive:False positive:False positive:False positive:

. . . individuals without the condition who . . . individuals without the condition who are falsely identified as diseased by the are falsely identified as diseased by the new testnew test””. This is also referred to as a . This is also referred to as a mis-diagnosis.mis-diagnosis.

. . . individuals without the condition who . . . individuals without the condition who are falsely identified as diseased by the are falsely identified as diseased by the new testnew test””. This is also referred to as a . This is also referred to as a mis-diagnosis.mis-diagnosis.

True negativeTrue negativeTrue negativeTrue negative

““ . . . individuals without the condition . . . individuals without the condition who are correctly identified as who are correctly identified as diseased-free by the new testdiseased-free by the new test””

““ . . . individuals without the condition . . . individuals without the condition who are correctly identified as who are correctly identified as diseased-free by the new testdiseased-free by the new test””

False negative:False negative:False negative:False negative:

““ . . . individuals with the condition who . . . individuals with the condition who are falsely identified as disease-free by are falsely identified as disease-free by the new testthe new test””. This is also referred to as . This is also referred to as a missed diagnosis.a missed diagnosis.

““ . . . individuals with the condition who . . . individuals with the condition who are falsely identified as disease-free by are falsely identified as disease-free by the new testthe new test””. This is also referred to as . This is also referred to as a missed diagnosis.a missed diagnosis.

• ““ . . . probability that an individual with a . . . probability that an individual with a positive test result has the disease. positive test result has the disease.

• PVP is also known as the PVP is also known as the posterior posterior probability, positive predictive valueprobability, positive predictive value or or posttest probabilityposttest probability or disease or disease””

• ““ . . . probability that an individual with a . . . probability that an individual with a positive test result has the disease. positive test result has the disease.

• PVP is also known as the PVP is also known as the posterior posterior probability, positive predictive valueprobability, positive predictive value or or posttest probabilityposttest probability or disease or disease””

• ““ . . . probability that an individual with a . . . probability that an individual with a negative test result does not have the negative test result does not have the disease. disease.

• PVN is also known as PVN is also known as negative predictive negative predictive valuevalue””

• ““ . . . probability that an individual with a . . . probability that an individual with a negative test result does not have the negative test result does not have the disease. disease.

• PVN is also known as PVN is also known as negative predictive negative predictive valuevalue””

Predictive Value PositivePredictive Value Positive (PVP) (PVP)Predictive Value PositivePredictive Value Positive (PVP) (PVP)

Predictive Value NegativePredictive Value NegativePredictive Value NegativePredictive Value Negative

• Predictive value of a positive test is Predictive value of a positive test is the proportion of patients with the proportion of patients with positivepositive tests who have disease. tests who have disease.

• This is the same thing as posttest This is the same thing as posttest probability of disease given a positive probability of disease given a positive test. It measures how well the test test. It measures how well the test rules in disease. rules in disease.

• Predictive value of a positive test is Predictive value of a positive test is the proportion of patients with the proportion of patients with positivepositive tests who have disease. tests who have disease.

• This is the same thing as posttest This is the same thing as posttest probability of disease given a positive probability of disease given a positive test. It measures how well the test test. It measures how well the test rules in disease. rules in disease.

aa b b

cc d d





TTEESSTT

Positive Predictive Value (PV+) = (a/a+b) X 100 (%)Positive Predictive Value (PV+) = (a/a+b) X 100 (%)

+ PV = a/ (a+b)

• = Posttest probability= Posttest probability• = = the proportion of patients with the proportion of patients with positivepositive

tests who have diseasetests who have disease

• = Posttest probability= Posttest probability• = = the proportion of patients with the proportion of patients with positivepositive

tests who have diseasetests who have disease

aa b b

cc d d





TTEESSTT

Negative Predictive Value (PV-) = (d/c+d) X 100 (%)Negative Predictive Value (PV-) = (d/c+d) X 100 (%)

Proportion of true negatives among all Proportion of true negatives among all those with negatives resultsthose with negatives results

- PV = d/ (c+d)

Note that ………………………..Note that ………………………..

Positive and negative predictive Positive and negative predictive values are calculated using both values are calculated using both those with disease, and those those with disease, and those without diseasewithout disease

Therefore, both positive and negative Therefore, both positive and negative predictive values are affected by predictive values are affected by prevalence of the target conditionprevalence of the target condition

Pneumonia

No Pneumoni

a

Pneumonia

NoPneumonia

RESPIRATORY

CHEST X-RAY

a b

c d - PV = d/ (c+d)

+ PV = a/ (a+b)

Sensitivity a / (a+c)

Specificity d / (b+d)

Pneumonia

No Pneumoni

a

Pneumonia

NoPneumonia

RESPIRASI

FOTO RONTGEN

a b

c d

Accuracy = (a+d) / N

Prevalence = (a+c) / N

a/a + cLR + = ----------

b/b + d

c/a + cLR - = ----------

d/b + d

Pneumonia

No Pneumoni

a

Pneumonia

NoPneumonia

RESPIRASI

FOTO RONTGEN

a b

c d

Probability of having the test result positive among those who have disease

Probability of having the test result positive among those who have disease

Likelihood ratio positive:Likelihood ratio positive:

Probability of having the test result negative among those who don’t have disease

Probability of having the test result negative among those who don’t have disease

Likelihood ratio negative:Likelihood ratio negative:

Diagnostic test for anemia using ferritin

Test-Treatment Threshold

Post-test probabilityPost-test probability

LIKELIHOOD RATIO

• Probability of having a test result (positive or negative) in a person with disease compared to the test result (positive or negative) of person with disease free

LR (+) = 12,3 LR (-) = 0,39

What does this mean?

1. Is this evidence about the accuracy of a

diagnostic test valid?

Primary questions for Diagnostic Test

2. Does this (valid) evidence demonstrate an important ability of this test to accurately distinguish patients who do and don’t have a specific disorder?

3. Can I apply this valid, important diagnostic test to a specific patient?

1. Was there an independent, blind comparison with a reference (“gold”) standard of diagnosis?

2. Was the diagnostic test evaluated in an appropriate spectrum of patients (like those in whom we would use it in practice)?

3. Was the reference standard applied regardless of the diagnostic test result?

4. Was the test (or cluster of tests) validated in a second, independent group of patients?

Is this evidence about a diagnostic test valid?


diagnostic test in questiondiagnostic test in question

• history or • physical

examination, • a blood test

• history or • physical

examination, • a blood test

“gold” standard“gold” standard

• autopsy or • biopsy • autopsy or • biopsy

BLINDING

highhigh

mediummedium

low clinical suspicionlow clinical suspicion

35 35 positipositiveve

35 35 positipositiveve

Carcino Embryonic Carcino Embryonic Antigen (CEA)Antigen (CEA) mildmild colon/ colon/

RectRectal canceral cancermildmild colon/ colon/

RectRectal canceral cancer

otherother gastro gastro--intestinal intestinal cancercancer

otherother gastro gastro--intestinal intestinal cancercancer

36 36 advanced advanced colon/colon/ rectumrectum

cancercancer

36 36 advanced advanced colon/colon/ rectumrectum

cancercancer

PoorPooraccuracyaccuracy

PoorPooraccuracyaccuracy

Do more good

Invasive

Was the reference standard applied regardless of the diagnostic test result?

Was the reference standard applied regardless of the diagnostic test result?

Standard

Standard

Do more harm

Non invasiveNEGATIF

Disease (+)

Disease (-)

Disease (+)

Disease (-)

Was the test (or cluster of tests) validated in a second, independent group of patients?

Study Patiens

IndependentGroup

1. Is the dx test available, affordable, accurate, and precise in our setting?

2. Can we generate a clinically sensible estimate of our patient’s pre-test probability?

· From personal experience, prevalence statistics, practice databases, or primary studies· Are the study patients similar to our own?· Is it unlikely that the disease possibilities or probabilities have changed since this evidence was gathered?

3. Will the resulting post-test probabilities affect our management and help our patient?

· Could it move us across a test-treatment threshold?· Would our patient be a willing partner in carrying it out?· Would the consequences of the test help our patient reach his or her goals in all this?

Table 2 applying a valid diagnostic test to anindividual patient

Table 2 applying a valid diagnostic test to anindividual patient

1. Is the dx test available, affordable, accurate, and precise in our setting?

availableavailable

affordableaffordable

accurateaccurate

PrecisePreciseEXPERT????

2. Can we generate a clinically sensible estimate of our patient’s pre-test probability?• From personal experience, prevalence

statistics, practice databases, or primary studies

Diagnostic tests that produce big changes from pretest to post-test probabilities are important and

likely to be useful to us in our practice

Diagnostic tests that produce big changes from pretest to post-test probabilities are important and

likely to be useful to us in our practice

“pre-test” probability (what we estimated before the test)

“pre-test” probability (what we estimated before the test)

“post-test” probability(what we estimates after the test)

“post-test” probability(what we estimates after the test)

2. Can we generate a clinically sensible estimate of our patient’s pre-test probability?• Are the study patients similar to our own?• Is it unlikely that the disease possibilities or

probabilities have changed since this evidence was gathered?

Widal

AppendicitisHipertension

Typhoid???Typhoid???

Mc Burney vs. USGMc Burney vs. USG

Criteria of hipertensionCriteria of hipertension

Sensitivity =Specificity = LR + =LR – =PPV =NPV =Prevalence =Pre-test odds =Post-test odds =Post-test prob =

731 270 100178 1500 1578809 1770 2579

Dx testresult(ferritin)

(+) (<65ml/L)(-) (>65ml/L)

Target disorder(iron deficiency anemia) Totals

Present Absent

a/(a + c) = 731/809 = 90%d/(b + d) = 1500/1770 = 85%sens/(1 – spec) = 90%/15% = 6(1 – sens)/spec = 10%/85% = 0.12a/(a + b) = 731/1001 = 73%d/(c + d) = 1500/1578 = 95%(a + c)/(a + b + c + d) = 809/2579 = 32%.prevalence/(1 – prevalence) = 31%/69% = 0.4pre-test odds × likelihood ratio.post-test odds/(post-test odds + 1).

DIAGNOSTIC & SCREENING Evidence-based Medicine. Pengalaman/Data Empiric Masalah experience-based...

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Transcript of DIAGNOSTIC & SCREENING Evidence-based Medicine. Pengalaman/Data Empiric Masalah experience-based...