1. Dr K N Prasad Community Medicine
Screening methods
Dr K N Prasad
Community Medicine

2. Diseases are having iceberg phenomenon
Screening is the early detection of disease precursors to disease. Or susceptibility to diseases in individuals who do not show any signs of the disease
Tests
Questions
Examinations
Laboratory tests
X rays

3. Definition: “The PRESUMPTIVE identification of UNRECOGNIZED disease or defect by the application of tests, exams or other procedures which can be applied RAPIDLY to sort out apparently well persons who PROBABLY have a disease from those who PROBABLY do not.”
Screening refers to the application of a medical procedure or test to people who as yet have no symptoms of a particular disease, for the purpose of determining their likelihood of having the disease.
The screening procedure itself does not diagnose the illness.
Screening test will need further evaluation with subsequent diagnostic tests or procedures.

5. Differences Screening test Diagnostic test Done on apparently healthy
Applied to groups
Based on one or cut off criteria
Less accurate
Not a basis for treatment
Initiative comes from the health agency
Diagnostic test
Done on those with sick or indications
Applied to single patient
Based on evaluation of number of symptoms, signs or lab tests
More accurate
Basis for treatment
Initiative comes from patient with complaint

6. Lead time concept
Time lag present between disease onset and usual time of diagnosis
Final critical
point
Usual time of
diagnosis
Disease
onset
First possible
detection
outcome A
Screening time B
Lead time
Lead time is the period between diagnosis by early detection and
diagnosis by other means

7. Screening pathways Healthy Disease or precursor Detectable
Symptoms develop
Advance disease
Death
Screening possible
Intervention to avert disease development or its consequences
Life prolonged

8. Objective Examinations
The goal of screening is to reduce morbidity or mortality from the disease by detecting diseases in their earliest stages, when treatment is usually more successful.
Sort out the population who has risk from others
Examinations
Pap smear, Mammogram, Clinical breast exam, Blood pressure determination, Cholesterol level, Eye examination/vision test, and Urinalysis.

9. Uses of screening tests
Cases detection (Prescriptive )
Screened primarily for their own benefit Ex. Neonatal, cancers
Control of diseases (Prospective)
Screened for benefit of others
Ex. STD, TB
Research purpose
May aid in obtaining basic knowledge about natural history of disease
Education opportunity
To create public awareness and educating health professionals

10. Types of screening Mass screening High risk or selection screening
Screening afford to all irrespective of the particular risk Ex. TB
High risk or selection screening
Applied to selective high risk group on the basis of epidemiological research
Ex. Cervical Cancer, heart diseases
Multi purpose screening
Application of two or more tests in combination to a large number at one time
Ex. Questionnaire, examination, laboratory tests etc.

11. Criteria for population based screening
Knowledge of disease
Condition must be an important problem
Presence of recognisable latent or early symptomatic stage
Natural history of the condition must be adequately understood
Feasibility of screening procedures
Suitable test or examination
Acceptable to the population
Should be a continuous process

12. Contd. Diagnosis and treatment Cost considerations
acceptable treatment with recognisable disease
Facilities for diagnosis & treatment should be available
agreed upon policy to treat as patients
Cost considerations
adequate resources
Expected benefit

13. Principles Condition should be an important public health problem
There should be a recognizable early or latent stage
There should be an accepted treatment for persons with condition
The screening test is valid, reliable and acceptable yield
The test should be acceptable to the population to be screened
The cost of screening and case finding should be economically balanced in relation to medical care as a whole

14. Screening tests Acceptability : Repeatability
Simple, minimum pain or discomfort, easy, safety, rapidity , acceptable procedure, etc.
Repeatability
Must give consistent result when repeated several times on the same subject or individual
Observer variation
Biological variation

15. Observer variation Intra observer or within observer variation
Measurements should be same( subject or material) if recorded several times at that time or event
Ex. Ht, wt, lab tests. etc..
Inter observer variation or between observer variation
Differences in measurements on the same ( subject or material) by different investigators
Ex. X ray, blood smears, organisms, etc..

16. Biological variation
Variation in physiological variables. Ex. BP, Rates, etc.
Changes in parameters observed
Ex. MI, Cancers, etc
Variations in their symptoms /signs
Memory, pain, quality of care, etc.
Regression to the mean
Tendency of values merge at the mean.
This is tested by repeated observation over time

17. Thought for the day
Every job is a self portrait of the person who did it.
Autograph your work with excellence.

18. Thank you

20. Difference Screening test is intended for initial examination.
Diagnosis involves confirmation of presence or absence of disease in someone suspected or at risk for having a disease.
Case finding measures