1. DR.FATIMA ALKHALEDY M.B.Ch.B;F.I.C.M.S/C.M
SCREENING
DR.FATIMA ALKHALEDY
M.B.Ch.B;F.I.C.M.S/C.M

2. SCREENING Outline: Definition of Screening.
Differentiation between Screening and Diagnostic test?
Uses/Purpose of Screening.
Types and Examples of Screening test.
Criteria for successful screening program.
Relation ship between sensitivity and specify.
Risk of Screening.

3. How We Can Define Screening ….?

4. Definition The early detection of: Disease Precursors of Disease
Susceptibility to Disease
In individuals who do not show any signs of disease.

5. means of rapidly applied tests in apparently healthy individuals.
Definition
The presumptive identification of those who probably have disease from those who do not have by
means of rapidly applied tests in apparently healthy individuals.

6. Definition

7. Definition
Screening

8. How we can Differentiate Between Screening and Diagnostic Tests ….?

9. Differentiate Between Screening and Diagnostic Tests
Asymptomatic
Suggestive clinical picture
Large group
Single subject
Less accurate
Accurate
Not conclusive
Conclusive
Less expensive
Expensive
Not basic for treatment
Basic to treatment

10. What are the Uses of Screening ….?

11. Uses of Screening Uses of Screening Case Detection
Perspective Screening
Case / Disease Control
Prospective Screening
Research
Natural History of Disease
Health Education
Public Awareness

12. Purpose of Screening Reducing disease burden.
Classifying people to likelihood of having a particular disease.
Mean of identifying high risk groups who warrant further evaluation.

13. Screening Process

14. Types of Screening Test
What are the Type of Screening Tests …?

15. Types of Screening Test
Mass
High Risk
Multiphasic

16. Types of Screening Test Population Approach
Not Cost Effective
Potential To Alter The Root Cause Of Disease
Large Chance To Reduce Disease Incidence
Small Benefit To The Individual
Poor Subject Motivation
Large Chance Of Reducing Disease Incidence

17. Types of Screening Test High Risk Strategy
Cost Effective
Intervention Appropriate To Individual
Fails To Deal With Root Cause Of Disease.
Subject Motivated
Small Chance Reducing The Diseases Incidence

18. Can You Give Some Examples For Screening Tests … ?

19. Examples for Screening Tests
Infancy
Pregnancy
Elderly
Adults
Growth Charts
Weight
Cancers
Lipid profile
Metabolic Screening
CBC
Depression
Blood pressure
Hearing Test
Blood sugar
Vitamin deficiencies
BMI

20. Criteria For Successful Screening Test:
Criteria for Disease
Criteria for Test

21. Criteria For Successful Screening Test:
Criteria for Disease:
Present in population screened.
High burden &of high public health concern.
Screening +Intervention must improve outcome.
Known natural history of the disease.

22. Criteria For Successful Screening Test:
Criteria for Test:
Reliable.
Valid.
Simple and inexpensive.
Very safe.
Acceptable to subjects and providers.
Cost-effective.
Exit strategy.

23. Criteria For Successful Screening Test:
Exit strategy:
Facilities for diagnosis and appropriate treatments should be available for positive subjects.
Ethically not acceptable to offer screening without available management.

24. Criteria For Successful Screening Test:
RELIABILTY:
What Is The Definition Of Reliability ?
What Are The Causes Of Unreliability ?

25. Criteria For Successful Screening Test:
Definition of Reliability:
Repeatability, Reducibility, Precision.
Getting the same results, when the test repeated in same target individuals in the same settings.

26. Criteria For Successful Screening Test:
Causes of unreliability:
Observer variation.
Subject variation – Biological.
Technical method error variation.

27. Criteria For Successful Screening Test:
ACCEPTABILITY:
The test should not be:
Painful.
Unsafe.
Discomforting /Embarrassing.
Socially/ believes not accepted.

28. Criteria For Successful Screening Test:
VALIDITY:
Ability of the test to distinguish between who has the diseases and who does not.

29. Validity
Sensitivity
Specificity
Predictive Value
Yield

30. DISEASE TOTAL TEST Diseased No disease Test +ve a b a+b Test -ve c d
a+c
b+d
a+b+c+d

31. Ability of the test to truly identify those who have the disease
Sensitivity
DISEASE
TOTAL
TEST
Diseased
No disease
Test +ve a b
a+b
Test -ve c d
c+d
a+c
b+d
a+b+c+d
Ability of the test to truly identify those who have the disease
Sensitivity= a/(a+c)
True Positive

32. Sensitivity
[[A 90% Sensitivity means that 90% of the diseased people screened by the test will give a “true positive” and the remaining 10% a “false negative results”]]
Positive test and have the disease.
Negative test and have the disease.

33. Specificity Specificity= d/(b+d) True Negative DISEASE TOTAL TEST
Diseased
No disease
Test +ve a b
a+b
Test -ve c d
c+d
a+c
b+d
a+b+c+d
The ability of the test to correctly identify those who do not really have the disease
Specificity=
d/(b+d)
True
Negative

34. Specificity
[[A 90% Specificity means that 90% of the non diseased people screened by the test will give a “true negative” result, and the remaining 10% a “false negative results”]]
Negative test and do not have the disease.
Negative test and have the disease.

35. False Positive error rate= (1-specificity)
False Negative error rate = (1-sensitivity)

36. Assume a population of 1,000 people 100 have a disease 900 do not have the disease A screening test is used to identify the 100 people with the disease
Sensitivity = 80/ 100 X 100= 80%
Specificity = 800/ 900 X 100 = 88%

37. Practical Example Brain Tumor EEG Results Present Absent Positive 36
54,000
Negative 4
306,000
Total 40
360,000
Sensitivity = 36/40 X 100 = 90%
Specificity = 306,000/360,000 X 100 = 85%

38. DISEASE TOTAL TEST Diseased No disease Test +ve a+b Test -ve c+d a+c
a (True Positive)
b (false Positive)
a+b
Test -ve
c (false Negative)
d (True Negative)
c+d
a+c
b+d
a+b+c+d

39. Predictive value DISEASE TOTAL TEST No disease Test +ve a b a+b
Positive Predictive value
Proportion of Individuals with positive test really have the disease
PPV=a/(a+b)
Negative Predictive value
Proportion of Individuals with negative test really have no disease
NPV= d/(c+d)
DISEASE
TOTAL
TEST
Diseased
No disease
Test +ve a b
a+b
Test -ve c d
c+d
a+c
b+d
a+b+c+d

40. Practical Example Screening Test Results Diagnosis Total Diseased
Not Diseases
Positive 40 20 60
Negative
100
9840
9940
140
9860
10,000
Sensitivity = 40/140 X100 = 28.57%
Specificity = 9840/9860 X100 =99.79%
Positive predictive value = 40/60X100 = 66.66%
Negative predictive value = 9840/9940X100 = 98.9%

41. Effects on Predictive Value
Prevalence Increases
PPV Increases; NPV Decreases
Prevalence Decreases
PPV Decreases; NPV Increases
Specificity Increases
PPV Increases
Sensitivity Increases
NPV Increases

42. Yield –the amount of previously unrecognized disease that is diagnosed and brought to treatment as a result of the screening program.

43. Practical Exercise

44. What is better a test with high sensitivity or with high specificity…?

45. Relation Between Sensitivity & Specificity
False Positive

46. Relation Between Sensitivity & Specificity
False Negative

47. Relation Between Sensitivity & Specificity

48. What
about
Risk of
Screening …?

49. Risk of Screening True Positive False Positive False Negative
Labelling Effect
False Positive
Anxiety
Fear From Future Test
Monetary Expenses
False Negative
Delayed Diagnosis
Delayed Intervention
Complications

50. Thank You