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Screening test

OLEH

dr.Siswanto,MSc

Ilmu kesehatan masyarakat

F.K. UNIBRAW.


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1. DEFINITION OF SCREENING

The presumptive identification of unrecognized

disease or defect by the application of test, examination,

or other procedures which can be applied rapidly to sortout apparently well persons who probably have a

disease from those who probably do not.

A screening test is not intended to be diagnostic. Personwith positive or suspicious findings must be referred to

their physicians for diagnosis.


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2. AIMS OF SCREENING TEST

To detect early stages of disease so that treatment can begiven ( diagnose dini)

3. DISEASE APPROPRIATE FOR SCREENING

a. Disease that often are fatal or have seriousconsequences with prolonged morbidity.

b. The disease must have a treatment that, when applied

to the screen-detected stage of the disease, is moreaffective than treatment applied after symptoms haveled to diagnosis.There is no point in screening for adisease that can be treat successfully after symptomsappear.

c. The detectable preclinical phase (DPCP) of diseaseshould have a high prevalence among the personsscreened.


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Two important concepts for screening :

1. Individuals with a disease can be identified by a

screening test before the time of routinediagnosis ( eg, when symptoms occur)

2. Treatment at the time of detection by screening,

as opposed to the time of routine diagnosis,

result in an improved chance of survival


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SUITABLE SCREENING TESTHigh validity ( Accuracy)

High reliability ( Precision)

Low cost

None or low side effects

Convenient and painless as possible


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Validity of the test : The extent to whichthe test is capable of correctly diagnosing

the present or absence of the diseaseconcerned.

Sensitivity : The ability of the test to detectpeople who actually have the disease(a/a+c)

Spesificity : The ability of the test to detectpeople who actually do not have the

disease. (d/b+d)


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BAKU EMAS

Baku emas yang dipakai sebagai

pembanding tidak boleh mengandung unsur

atau komponen yang diuji

Baku emas tidak boleh mempunyai

sensitivitas dan spesifitas lebih rendah dari

test screning yang diuji


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PREDICTIVE VALUE OF THE TEST

Positive predictive value. ( a/a+b)The probality that a person who tested positive on

the test actually had the disease.

Negative predictive value. ( d/c+d).

The probality that a person who tested negative truly

did not had the disease.

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Positive Predictive Value ( Nilai Duga

Positif)

Probabilitas seseorang sakit bila uji skrening positif

A / A + B

Negative Predictive Value ( Nilai Duga

Negatif)

Probabilitas seseorang tidak sakit bila uji skreningnegatif

D / C + D


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DISEASE

(GOLD STANDARD)SCREENING

-

TOTAL

SCREENING

TEST +

A

(TRUE POSITIVE)

B

(FALSE POSITIVE)

A + B

SCREENING

TEST -

C

(FALSE

NEGATIVE)

D

(TRUE NEGATIVE)

C + D

TOTAL A + C B + D A+B+C+D


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HASIL PATOLOGI ANATOMI

SCREENING

-

TOTAL

USG

KELENJAR

TIROID +

18 16 34

USG

KELENJARTIROID -

2 64 66

TOTAL 20 80 100

SENSITIVITAS : 18/20 + 100 % = 90 %

SPESIFISITAS : 64/80 + 100 % = 80 %

N D + : 18/34 = 53 %

N D - : 64/66 = 97 %


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Uses of specific tests

( A specific test should be chosen)

When false positive results can harm the patient

physically, emotionally or financially.

Exp: cancer

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RELIABILITY

The extent to which repeated measurement of a

relatively stable phenomenon fall closely to each

other.

Reproducibility and precision are otherwords for this property.

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VARIATION

Source Definition

Measurement

Instrument The means of making the

measurement

Observer The person making the

measurement

Biologic

Within individuals Changes in people with time and

situation

Among individuals Biologic differences from person to

person20


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Variation

Measurement Variation : All observation aresubject to variation resulting from measurement

because of the performance of the instrument and

observers.

Reduce

Standard protocols Machines ( Automatic)

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Variation

Fetal heart rate : Auscultation vs Electronicmonitoring

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RELIABILITY ( KEANDALAN,

REPRODUSIBILITAS)Suatu pengukuran disebut andal apabila alat test mem-

berikan nilai yang sama atau hampir sama apabila

pemeriksaan dilakukan ber ulang ulang.

Keandalan dipengaruhi oleh:

Variasi metoda

Variasi intra dan antar observer

Variasi subyek


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PENILAIAN KEANDALAN PENGUKURAN

1. Varibel numerik.

Dengan menghitung Koefisien Variasi ( KV) yaitu :hasil simpang baku (standard deviation) dibagi denganrerata ( mean).

Contoh : pengukuran kadar natrium serum dilakukandengan dua cara yaitu cara A dan cara B masing masingdilakukan 20 kali pemeriksaan dengan hasil sbb:

Cara A : 136, 132,133, 137, 134, 135, dst

Cara B : 135, 139, 132, 132, 130,136 dst

Cara A : Rerata 134,7 Simpang baku 1,76 KV= 0,013

Cara B : Rerata 134,7 Simpang baku 2,71 KV= 0,020

Pengukuran A lebih andal dari B


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2. Variabel nominalDengan menentukan nilai Kappa (k)

Hasil pemeriksaan thorax photo dari penderita yang dicurigai TBColeh dua dokter A dan B

NO DOKTER A DOKTER B NO DOKTER A DOKTER B

1 Normal Normal 16 Normal Abnormal

2 Abnormal Abnormal 17 Normal Normal

3 Normal Abnormal 18 Abnormal Normal

4 Normal Normal 19 Normal Abnormal

5 Normal Normal 20 Abnormal Abnormal

6 Abnormal Abnormal 21 Normal Abnormal


8 Abnormal Normal 23 Normal Abnormal


10 Normal Abnormal 25 Abnormal Normal

11 Normal Normal 26 Abnormal Normal

12 Normal Normal 27 Abnormal Abnormal

13 Abnormal Abnormal 28 Normal Abnormal

14 Abnormal Abnormal 29 Abnormal Abnormal15 Abnormal Normal 30 Normal Normal


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NORMAL TIDAK

NORMAL

A

9

B

7 16

TIDAK

C

4

D

10 14

13 17 30

Kesesuaian nyata = (9+10)/30 = 63,3 %

Kesesuaian karena peluang = (16x13)/30 + (14x17)/30 =14,9 %

Kesesuaian bukan karena peluang = (63,3-14,9) % =48,4 %

Potensi kesesuaian bukan karena

peluang (100-14,9) % = 85,1 %

ARTI KAPPA TEST


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ARTI KAPPA TEST

Under 20 % negligible

20% to 40% minimal

>40% to 60% fair

>60% to 80% good

>80% excellent28


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STRATEGI MENINGKATKAN KEANDALAN

1. Standarisasi cara pengukuran

Contoh : membuat Protap yaitu aturan yangterperinci untuk melaksakan pengukuran

Mengatasi kesalahan pada : pengamat dan subyek

2. Pelatihan pengamatMengatasi kesalahan pada :pengamat

Dengan peningkatan kemampuan dari pengamatuntuk melaksanakan pengukuran maka kemungkinan

kesalahan makin kecil.

Kesamaan kemampuan dari antar pengamat jugasangat diperlukan untuk meningkatkan keandalan.


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3. Penyempurnaan dan automatisasi instrumenMengatasi kesalahan dari alat ukur, pengamat dan subyek

Contoh : pemeriksaan kadar Hb dengan menggunakan

spektrofotometer jauh lebih baik dari pemeriksaan sahli

4. Mengulang pengukuran

Mengatasi kesalahan pada : pengamat, subyek dan alatukur.

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