5M

1. Define Screening

Screening is the process of identifying apparently healthy individuals who may have a disease or risk of disease.
It is done before symptoms appear.
Screening helps in early detection of disease.
It is applied to large groups or populations.
Screening tests are simple and quick.
They are not confirmatory tests.
Positive cases need further diagnostic tests.
Screening reduces disease burden in the community.
It is an important tool of preventive medicine.
It mainly works at secondary prevention level.

2. Aims of Screening

To detect disease at an early stage.
To identify individuals at risk.
To start early treatment and prevent complications.
To reduce morbidity and mortality.
To reduce severity of disease.
To improve quality of life.
To reduce cost of treatment.
To control spread of disease in community.
To help in planning health services.
To support preventive health care.

3. Types of Screening

Mass screening is done for whole population.
Selective screening is done for high-risk groups.
Multiple screening uses more than one test at a time.
Opportunistic screening is done during hospital visits.
Single disease screening targets one disease.
Multiphasic screening checks many diseases together.
Screening can be voluntary or compulsory.
It can be community based or hospital based.
Each type depends on disease and resources.
Proper selection improves effectiveness.

4. Uses of Screening in Community

Early detection of diseases in population.
Prevention of complications and disability.
Reduction in disease transmission.
Identification of hidden cases.
Helps in health planning and policy making.
Improves life expectancy.
Reduces treatment cost.
Increases awareness among people.
Helps in monitoring disease trends.
Strengthens preventive health services.

5. Iceberg Phenomenon of Disease

Only a small part of disease is visible clinically.
Large hidden part exists below surface.
Visible part includes diagnosed cases.
Hidden part includes undiagnosed and subclinical cases.
Most cases remain unnoticed without screening.
Screening helps to detect hidden cases.
Common in chronic and infectious diseases.
Important in public health planning.
Explains true burden of disease.
Guides preventive strategies.

6. Lead Time in Screening

Lead time is time gained by early detection.
It is the period between screening diagnosis and clinical diagnosis.
Screening detects disease before symptoms appear.
Lead time increases survival time artificially.
It does not always increase actual life span.
Important concept in screening evaluation.
Can give false impression of benefit.
Needs careful interpretation.
Common in cancer screening.
Should not be confused with cure.

7. Validity of Screening Test

Validity means ability to correctly identify disease.
It shows accuracy of screening test.
Measured by sensitivity and specificity.
High validity gives reliable results.
Valid test correctly classifies individuals.
Low validity gives false results.
Important for effective screening.
Depends on disease prevalence.
Essential for public health programs.
Improves trust in screening results.

8. Sensitivity of Screening Test

Sensitivity is ability to detect true positive cases.
It identifies people who actually have disease.
High sensitivity means few false negatives.
Important when missing disease is dangerous.
Used in serious and fatal diseases.
Calculated using true positives.
Sensitive tests are good for screening.
Helps in early case detection.
Negative result rules out disease.
Example: HIV screening tests.

9. Specificity of Screening Test

Specificity is ability to detect true negatives.
It identifies people who do not have disease.
High specificity means few false positives.
Important to avoid unnecessary anxiety.
Calculated using true negatives.
Specific test confirms disease absence.
Positive result rules in disease.
Important in confirmatory tests.
Reduces over-diagnosis.
Improves efficiency of screening.

10. Difference Between Screening Test and Diagnostic Test

Screening test is done on healthy people.
Diagnostic test is done on symptomatic patients.
Screening is simple and inexpensive.
Diagnostic test is complex and costly.
Screening is not confirmatory.
Diagnostic test confirms disease.
Screening has high sensitivity.
Diagnostic test has high specificity.
Screening is community based.
Diagnostic test is hospital based.

10M

Explain Screening in Detail – Notes Format (10 Marks)

Definition
Screening is the process of identifying disease or risk of disease in apparently healthy individuals.

Meaning
Done before appearance of symptoms
Applied to population groups
Detects disease in preclinical stage

Purpose
Early detection of disease
Early initiation of treatment
Prevention of complications and disability

Characteristics of Screening
Simple and rapid tests
Safe and acceptable
Low cost
Applied to large population
Not diagnostic or confirmatory

Procedure
Screening test is applied
Positive cases are identified
Further diagnostic tests are done
Treatment is started if confirmed

Level of Prevention
Mainly secondary prevention
Helps in halting disease progression

Importance
Reduces morbidity and mortality
Detects hidden cases
Improves quality of life
Reduces economic burden

Applications
Communicable diseases
Non-communicable diseases
Genetic and occupational diseases

Examples
Blood pressure check for hypertension
Blood sugar test for diabetes
Pap smear for cervical cancer
HIV screening
Mammography for breast cancer

Conclusion
Screening is an essential tool in preventive medicine and must be applied judiciously for maximum benefit.

Criteria for an Ideal Screening Test – Notes Format (10 Marks)

Disease Related Criteria
Disease should be an important public health problem
Disease should have high prevalence or serious outcome
Natural history of disease should be well understood
There should be a long preclinical or latent stage
Early treatment should be more effective than late treatment

Test Related Criteria
Test should be simple and easy to perform
Test should be rapid and give quick results
Test should be safe and non-invasive
Test should be acceptable to the population
Test should be cost-effective

Accuracy Criteria
Test should have high sensitivity
Test should have high specificity
False positive and false negative results should be minimal
Test should correctly classify individuals

Reliability Criteria
Test should give consistent results
Same result should be obtained on repeated testing
Observer variation should be minimal
Instrument and procedure should be standardized

Program Related Criteria
Facilities for diagnosis and treatment should be available
There should be proper referral system
Screening program should be continuous
Cost of screening should be balanced with benefits
Community participation should be ensured

Ethical and Social Criteria
Screening should do more good than harm
Psychological impact should be minimal
Confidentiality should be maintained

Conclusion
An ideal screening test must be accurate, reliable, acceptable, affordable, and useful in reducing disease burden in the community.

Sensitivity and Specificity – Notes Format (10 Marks)

Sensitivity
Sensitivity is the ability of a screening test to correctly identify individuals who have the disease
It measures true positive rate
A highly sensitive test detects most diseased persons
False negative results are minimal
Useful when missing a disease is dangerous
Best for screening purposes
Negative result helps to rule out disease

Formula
Sensitivity = True Positive / (True Positive + False Negative)

Specificity
Specificity is the ability of a screening test to correctly identify individuals who do not have the disease
It measures true negative rate
A highly specific test produces few false positive results
Useful to confirm diagnosis
Positive result helps to rule in disease

Formula
Specificity = True Negative / (True Negative + False Positive)

2 × 2 Table

Examples
HIV screening test – high sensitivity
Blood glucose test – high specificity
Pap smear – high sensitivity

Importance
Sensitivity reduces missed cases
Specificity reduces unnecessary investigations
Both are essential for effective screening programs

Validity and Reliability of Screening Tests – Notes Format (10 Marks)

Validity
Validity refers to the ability of a screening test to correctly identify individuals with and without disease
It indicates accuracy of the test
A valid test gives results close to the true value
Validity shows how well the test measures what it is supposed to measure

Measures of validity
Sensitivity – ability to detect true positive cases
Specificity – ability to detect true negative cases
Both sensitivity and specificity together decide validity

Importance of validity
Ensures correct classification of individuals
Reduces false positive and false negative results
Essential for effectiveness of screening programs
Improves trust in screening results

Reliability
Reliability refers to consistency or repeatability of test results
Same test gives same result on repeated examinations
It is not affected by disease prevalence
A reliable test may or may not be valid

Types of reliability
Intra-observer reliability – same observer gets same result
Inter-observer reliability – different observers get same result
Instrument reliability – same instrument gives consistent results

Factors affecting reliability
Observer skill and training
Quality of instrument
Standardized procedure

Difference between validity and reliability
Validity measures accuracy
Reliability measures consistency
A test can be reliable but not valid
A valid test is usually reliable

Conclusion
An ideal screening test should be both valid and reliable for successful disease detection in the community.

Iceberg Phenomenon of Disease – Notes Format (10 Marks)

Definition
Iceberg phenomenon describes the hidden part of disease in the community which is not visible clinically.

Concept
Only a small proportion of disease cases are clinically apparent
Large proportion of cases remain hidden in the community
Visible cases are just the tip of the iceberg

Visible part of iceberg
Clinically diagnosed cases
Severe and advanced cases
Hospitalized and reported cases

Hidden part of iceberg
Subclinical cases
Undiagnosed cases
Carrier state
Latent and early cases

Diagram (representation)

    Clinically visible cases
   -------------------------
          Water level
   -------------------------

Subclinical, latent, carrier cases

Examples
Hypertension
Diabetes mellitus
Tuberculosis
Leprosy
HIV infection

Importance of iceberg phenomenon
Shows true burden of disease in community
Explains why reported cases are less than actual cases
Helps in planning screening programs
Guides preventive and control measures
Important for public health planning

Role of screening
Screening helps to detect hidden cases
Reduces iceberg size by early detection
Prevents complications and transmission

Conclusion
Iceberg phenomenon highlights the need for screening and preventive strategies to control disease at community level.

Lead Time and Length Time Bias in Screening – Notes Format (10 Marks)

Lead Time Bias
Lead time is the time interval between detection of disease by screening and usual clinical diagnosis
Screening detects disease earlier than symptoms appear
Lead time increases apparent survival time
It does not necessarily increase actual life expectancy
Gives false impression that screening improves survival
Commonly seen in cancer screening programs

Example of lead time bias
Cancer detected early by screening appears to have longer survival
But actual time of death remains unchanged

Length Time Bias
Length time bias occurs because screening detects slow-growing diseases more easily
Slow-growing diseases remain longer in preclinical phase
Fast-growing aggressive diseases progress rapidly and are missed
Screening selects more mild cases
This gives false impression of better prognosis

Effects of length time bias
Overestimation of benefit of screening
Higher survival rate in screened population
Misinterpretation of screening effectiveness

Difference between lead time bias and length time bias
Lead time bias increases survival time artificially
Length time bias selects less aggressive cases

Importance
Both biases must be considered while evaluating screening programs
They affect interpretation of screening outcomes

Conclusion
Understanding lead time and length time bias is essential to correctly assess the true benefit of screening.

Uses and Limitations of Screening – Notes Format (10 Marks)

Uses of Screening
Early detection of disease in apparently healthy individuals
Detection of disease in preclinical or latent stage
Early initiation of treatment
Prevention of complications and disability
Reduction in morbidity and mortality
Identification of hidden cases in community
Reduction in cost of treatment
Improvement in quality of life
Control of communicable and non-communicable diseases
Helps in health planning and policy making

Public health importance
Helps to know true burden of disease
Supports preventive and promotive health services
Assists in evaluation of health programs
Creates health awareness among population

Limitations of Screening
False positive results cause anxiety and stress
False negative results give false reassurance
Over-diagnosis of disease
Over-treatment of mild cases
High cost if disease prevalence is low
Requires good diagnostic and treatment facilities
Poor follow-up reduces effectiveness
Ethical and psychological issues may arise
Not useful for all diseases
May not always reduce mortality

Conclusion
Screening is a useful public health tool, but it should be applied carefully after weighing benefits, risks, and available resources.

20M

20 Marks Question 1
Screening for Disease – Detailed Notes

Definition of Screening
Screening is the systematic application of tests or examinations to identify disease or risk of disease in apparently healthy individuals.
It is done before the appearance of signs and symptoms.
Screening helps in early detection of disease.
It is applied to groups or populations, not individuals.

Objectives of Screening
Early detection of disease
Early initiation of treatment
Prevention of complications and disability
Reduction in morbidity and mortality
Improvement in quality of life
Reduction in cost of treatment
Control of disease spread in community
Identification of high-risk individuals

Types of Screening

Mass screening
Screening of entire population
Done when disease is common
Example: Blood pressure screening

Selective screening
Screening of high-risk groups
More cost-effective
Example: Screening diabetics for retinopathy

Multiple screening
Use of more than one screening test
Detects multiple diseases
Example: Health check-up camps

Opportunistic screening
Done when person visits health facility for other reasons
Example: BP check during OPD visit

Criteria for an Ideal Screening Test

Disease related criteria
Disease should be an important public health problem
Natural history should be well understood
Long preclinical phase should be present
Early treatment should be beneficial

Test related criteria
Test should be simple and rapid
Test should be safe and acceptable
Test should be inexpensive
Test should have high sensitivity and specificity
Test should be valid and reliable

Program related criteria
Diagnostic and treatment facilities should be available
Good referral system should exist
Screening should be continuous
Cost should be balanced with benefit

Uses of Screening

Early detection of disease
Detection of hidden cases
Reduction of complications
Decrease in disease burden
Helps in health planning
Improves life expectancy
Creates health awareness
Supports preventive medicine programs

Limitations of Screening

False positive results cause anxiety
False negative results give false reassurance
Over-diagnosis of mild disease
Over-treatment
High cost if disease prevalence is low
Requires good follow-up services
Ethical and psychological issues
Not useful for all diseases

Examples of Screening

Blood pressure measurement for hypertension
Blood sugar estimation for diabetes mellitus
Pap smear for cervical cancer
Mammography for breast cancer
HIV screening tests

Conclusion
Screening is an important tool of preventive and social medicine.
When properly planned and implemented, it reduces disease burden and improves community health.

20 Marks Question 2
Screening Tests – Sensitivity, Specificity, Validity, Reliability, Predictive Values, 2×2 Table, Examples

Introduction
Screening tests are applied to apparently healthy individuals to detect disease at an early stage.
They are not diagnostic tests.
Their effectiveness depends on certain statistical properties.

2 × 2 Table

Sensitivity

Definition
Sensitivity is the ability of a screening test to correctly identify individuals who actually have the disease.

Explanation
High sensitivity means few false negative cases
Useful when missing a disease is dangerous
Preferred for screening purposes

Formula
Sensitivity = True Positive / (True Positive + False Negative)

Example
HIV screening test
Pap smear for cervical cancer

Specificity

Definition
Specificity is the ability of a screening test to correctly identify individuals who do not have the disease.

Explanation
High specificity means few false positive cases
Useful to confirm disease
Reduces unnecessary anxiety and investigations

Formula
Specificity = True Negative / (True Negative + False Positive)

Example
Pregnancy test
Blood glucose estimation

Validity

Definition
Validity refers to the accuracy of a screening test.
It indicates how well a test measures what it is intended to measure.

Explanation
A valid test correctly classifies individuals
Validity depends on sensitivity and specificity
High validity is essential for effective screening programs

Reliability

Definition
Reliability refers to consistency or repeatability of test results.

Explanation
Same test gives same result on repeated testing
Not affected by disease prevalence
A test can be reliable but not valid

Types of reliability
Intra-observer reliability
Inter-observer reliability
Instrument reliability

Predictive Values

Positive Predictive Value (PPV)
Probability that a person with positive test actually has disease
PPV = True Positive / (True Positive + False Positive)

Negative Predictive Value (NPV)
Probability that a person with negative test does not have disease
NPV = True Negative / (True Negative + False Negative)

Factors affecting predictive values
Disease prevalence
Sensitivity and specificity of test

Importance of Screening Test Properties

Helps in selecting appropriate screening test
Ensures early and correct detection of disease
Reduces false results
Improves effectiveness of public health programs

Examples of Screening Tests

Blood pressure measurement for hypertension
Blood sugar estimation for diabetes
Pap smear for cervical cancer
HIV screening tests
Mammography for breast cancer

Conclusion
An effective screening test should be sensitive, specific, valid, reliable, and have good predictive values to be useful in preventive and social medicine.

20 Marks Question 3
Iceberg Phenomenon of Disease – Detailed Notes

Introduction
Iceberg phenomenon explains the concept that only a small proportion of disease cases are visible clinically.
A large proportion of disease remains hidden in the community.
The visible cases represent only the tip of the iceberg.

Concept of Iceberg Phenomenon
Diseases exist in different stages in the community.
Only severe and diagnosed cases come to medical attention.
Majority of cases remain undetected without screening.
Hidden cases contribute to disease burden and transmission.

Components of Iceberg

Visible part of iceberg
Clinically diagnosed cases
Severe and advanced cases
Hospitalized and reported cases

Hidden part of iceberg
Subclinical cases
Undiagnosed cases
Carrier state
Latent infections
Mild and early cases

Diagram (representation)

    Clinically visible cases
   -------------------------
          Water level
   -------------------------

Subclinical, latent, carrier cases

Examples of Iceberg Phenomenon

Communicable diseases
Tuberculosis
Leprosy
HIV infection

Non-communicable diseases
Hypertension
Diabetes mellitus
Coronary artery disease

Importance of Iceberg Phenomenon

Shows true magnitude of disease in community
Explains gap between reported and actual cases
Highlights need for screening programs
Helps in planning preventive strategies
Important for resource allocation
Guides health policy and disease control measures

Role of Screening in Iceberg Phenomenon

Screening helps to detect hidden cases
Reduces iceberg size by early detection
Prevents complications and transmission
Improves disease control

Public Health Significance

Important concept in preventive and social medicine
Helps in understanding epidemiology of disease
Essential for community diagnosis

Conclusion
Iceberg phenomenon emphasizes that visible cases represent only a small part of disease burden and underlines the importance of screening and preventive measures in public health.