DIAGNOSISPutri Eyanoer, MD.,Ms.Epi.,Ph.D

1. Disease confirmation2. To sort other possibilities ~ sensitivity and

specificity3. Screening purpose ~ searching asymptomatic

patients4. Therapeutic purpose ~ identification of disease and

complication, treatment and therapy options,prediction of prognosis, and confirmation of otherpositive result

5. Epidemiologic studies

Biologic onset of the condition

Pathologic evidence of disease detectable by screening

Sign and symptoms of disease

Health care sought

Diagnosis of disease

Treatment of disease

PHYSICAL EXAMINATION

ADDITIONAL EXAMINATION

ANAMNESE

ADDITIONAL EXAMINATION

SERIAL TESTING

SENSITIVITY ↓SPECIFICITY ↑

ADDITIONAL EXAMINATION

PARALEL

SENSITIVITY ↑SPECIFICITY ↓

POSITIVE

NEGATIVE

IDEALLY…

FALSE NEGATIVE

FALSE POSITIF

MORE OFTEN…

1. Simple, cheap and non-invasive

2. Earlier detection / diagnosis at an earlier stage

DISEASE

TEST RESULT

Yes No Total

Yes TP FP TP+FP

No FN TN FN+TN

Total TP+FN FP+TN Total

TP=True Positive ; FP=False Positive ; TN=True Negative ; FN=False Negative

Diseased

Healthy classified as diseased

(false positive)

Diseased classified as healthy

(false negative)

Classified asdiseased

Diseased classifiedas diseased

Population

MODEL FOR SENSITIVITY AND SPECIFICITY

Penyakit (+) Penyakit (-)

Test (+) aTrue Positive

bFalse Positive

Test (-) cFalse-Negative

dTrue Negative

ACCURACY OF A TEST RESULT

Penyakit (+) Penyakit (-)

Test (+) aTrue Positive

bFalse Positive

Test (-) cFalse-Negative

dTrue Negative

SENSITIVITY AND SPECIFICITY

aa + c

Sensitivitas =

Spesifisitas = db + d

x 100 %

x 100 %

SENSITIVITY AND SPECIFICITYEXAMPLE : BLOOD GLUCOSE LEVEL

Diabetes : + Diabetes : - TotalTest :+ 34 20 54

Test : - 116 9830 9946

Total 150 9850 10.000

Diabetes : + Diabetes : - TotalTest :+ 66 98 164

Test : - 84 9752 9836Total 150 9850 10.000

Tingkat Pemotongan : 130 mg/100 ml

Tingkat Pemotongan : 180 mg/100 ml

Sensitivitas =34/150 x 100 % = 22.6 %

Spesifisitas =9830/9850x 100 % = 99.7 %

Sensitivitas =66/150 x 100 % = 44 %

Spesifisitas =9752/9850x 100 % = 99 %

SENSITIVITY AND SPECIFICITY

Ca : + Ca : - Total

FNA : + 14 8 22

FNA : - 1 91 92

Total 15 99 114

Sensitivity = 1414 +1

x 100 % =93 %

Specificity = 9191 + 8

x 100 % =92 %

POSITIVE AND NEGATIVE PREDICTIVE VALUE

Ca : + Ca : - Total

FNA : + 14 8 22

FNA : - 1 91 92

Total 15 99 114

14 + 8

(PV+) = aa + b x 100 %

PV+ = 14 x 100 % = 64 %

(PV-) = dd + c x 100 %

9191 + 1 x 100 % = 99 %PV- =

SUMMARY TABLE

SENSITIVITY SPECIFICITY PPV NPV

Proportion of patients with the target of disorder who had a positive test result

Proportion of patients with the target disorder who had a negative test result

Proportion of patients with positive test results who have the target disorder

Proportion of patients with negative test results who do not have the target disorders

Ability to detect disease Ability to detect that a healthy person among sick ones

Probability of disease in a patient with (+) test result

Probability of not having the disease when the test result is (-)

Should give (+) result among unhealthy group

Should give (-) result among healthy group

Chosen when there is important penalty for missing the disease (dangerous but treatable:tb,syphillis)

Used to confirm a diagnosis ~ needed when false(+) result can harm the patient (traumatic case, chemotherapy)

= A : (A+C) = D : (C+D) = A : (A+B) = D : (C+D)

POSITIVE PREDICTIVE VALUE

100

60

80

40

20

0 1/5 1/10 1/50 1/100 1/1000 1/10.000

SENSITIVITY/SPECIFICITY80/80

90/9099/99

PREVALENCE

PO

SIT

IVE

PR

ED

ICTI

VE

VA

LUE

(%)

LIKELIHOOD RATIOS

Define as :The PROBABILITY of that test result in people withdisease divided by the PROBABILITY of the test result inpeople without the disease

ODDS

Disease are MORE LIKELY in the presence of an extremely ABNORMAL TEST RESULT than it is for

marginal one

LIKELIHOOD RATIOS

POSITIVE LIKELIHOOD RATIO (LR+) Giving the magnitude of a possible positive test among those un-healthy compare to those healthy .

= { a/(a+c)} / {b/(b+d)} = SENSITIVITY / (1- SPECIFICITY)

NEGATIVE LIKELIHOOD RATIO (LR-) Giving the magnitude of a possible negative test among thoseun-healthy compare to those healthy

= { c/(a+c)} / {d/(b+d)} = (1- SENSITIVITY ) / SPECIFICITY

• Pd uji diagnostik kita menentukan bagaimana suatu uji dpt memisahkan antara subjek yg sakit dgn yg tdk sakit.

• CONTOH:

• Suatu uji diagnostik thd 100 pasien limfoma malignum yg dibuktikan dgn biopsi, 65 menunjukkan hasil positif; sdgkanuji diagnostik yg sama thd 100 pasien dgn pembesaran kelenjar non-limfoma, hanya 30 yg menunjukkan hasil uji positif. Bila dilakukan uji hipotesis dgn X2, tdpt hubungan yg bermakna (p<0,001) antara hasil uji positif dgn tdptnya limfoma malignum.

Penyakit

Hasil uji

Limfoma Non limfoma Total Positif PB

65PS30

PB+PS

Negatif NS35

NB70

NB+NS

Total PB+NS100

PS+NB100

Total200

Sensitivitas = A : (A+C) = 65 : 100 = 65%Spesifisitas = D : (B+D) = 70 : 100 = 70%

Histopatologi

Mammografi

Ca Non Ca JlhPositif 13 4 17Negatif 3 28 31

Jlh 16 32 48

SENSITIVITY: A/(A+C)

SPESIFICITY:D/(B+D)

LR+:SENS/

(1-SPEC)

LR-:(1-SENS)

/SPEC

PRE-TEST PROBABILITY

= PREVALENCE:(A+C ) / (A+B+C+D)

(13/16)X100%

= 81,25%

(28/32)X100%

=87,5%

(13/16)/(1-28/32)

=6,5

1-(13/16)/(28/32)

=0,21

16/48

= 33,3%

PRE TEST ODDS=PREVALENCE:

(1-PREVALENCE)

POST TEST ODDS=PRE TEST ODDS X LR+

POST-TEST PROBABILITY=POST TEST ODDS:

(1+POST TEST ODDS)

(16/48) : (1-16/48)

= 0,5

0,5 X 6,5

= 3,25

3,25 : (1+3,25) = 0.764 = 76,4%

Pretest probability Post test probability

33.3% 76.4%