Introduction to Screening and Diagnostic Tests

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Questions and Answers

What is the primary aim of screening in healthcare?

To identify disease early for intervention and management. (correct)

To provide comprehensive treatment plans for diagnosed diseases.

To perform extensive research on existing diseases.

To replace diagnostic tests in symptomatic individuals.

Which of the following best differentiates a screening test from a diagnostic test?

Diagnostic tests require specialized facilities to perform.

Screening tests are applied to asymptomatic individuals. (correct)

Screening tests are used for symptomatic individuals.

Diagnostic tests are typically mass-administered.

Which type of screening involves testing a population without considering high-risk groups?

Multiphasic screening

Opportunistic screening

Mass or population screening (correct)

Targeted screening

What does the predictive value positive indicate in a screening test?

The likelihood of a positive test result correctly identifying disease presence. Signup and view all the answers

Which of the following is NOT a purpose of screening?

Controlling treatment costs Signup and view all the answers

What is an example of opportunistic screening?

Conducting a screening during a medical visit for unrelated issues. Signup and view all the answers

Which of the following is a characteristic of selective (targeted) screening?

It identifies high-risk groups for disease testing. Signup and view all the answers

In the context of screening tests, what does specificity refer to?

The percentage of true negatives among those who don't have the disease. Signup and view all the answers

What type of screening would involve a cervical screening procedure?

Mass or population screening Signup and view all the answers

Which of the following is true regarding multiphasic screening?

It involves administering multiple tests at once for various diseases. Signup and view all the answers

Which of the following correctly defines sensitivity in the context of a screening test?

The ability to correctly identify all individuals who have the disease. Signup and view all the answers

What is the primary relationship between true positives (TP) and false negatives (FN) regarding sensitivity?

Increasing TP reduces FN. Signup and view all the answers

How is the positive predictive value (PVP) calculated?

PVP = [TP] / [TP + FP] Signup and view all the answers

Which factor does NOT influence the predictive value of the positive test (PVP)?

Cost of the screening test Signup and view all the answers

In the formula for specificity, the denominator represents which group?

Only those who do not have the disease. Signup and view all the answers

What is the relationship between false positives (FP) and specificity (SP)?

FP is inversely related to SP. Signup and view all the answers

Which formula correctly describes the false negative rate (FN%)?

FN% = [FN] / [TP + FN] Signup and view all the answers

Which of the following options is NOT considered an additional component of a good screening test beyond sensitivity and specificity?

Efficacy Signup and view all the answers

What does the term 'criterion standard test' refer to in diagnosis?

The most reliable test used as a benchmark for comparison. Signup and view all the answers

Which of these best describes a false positive (FP)?

A test result indicating disease when there is none. Signup and view all the answers

Which of the following is NOT a criterion for the disease to be screened?

The disease must incur a high treatment cost. Signup and view all the answers

Which aspect is essential for the acceptability of a screening test?

The people at whom it is aimed must find it acceptable. Signup and view all the answers

What does repeatability in a screening test primarily refer to?

The precision of results when the test is repeated on the same individual. Signup and view all the answers

Which of the following factors contributes to biological variation in screening tests?

Differences in patient responses and perceptions. Signup and view all the answers

What is meant by the accuracy of a screening test?

The test's capability to distinguish those with the disease from those without. Signup and view all the answers

What should be ensured regarding the expected benefits of early detection in a screening program?

They should exceed the risks and costs associated with testing. Signup and view all the answers

Which statement about inter-observer variation is correct?

It is the variation between different observers assessing the same subject. Signup and view all the answers

Which of the following describes a factor that is NOT directly related to the reliability of a screening test?

Public perception of the disease. Signup and view all the answers

Which of the following must be understood for a condition to fulfill screening criteria?

The natural history of the condition. Signup and view all the answers

What does the term 'error relating to technical methods' NOT include?

Biological changes in the subject. Signup and view all the answers

Study Notes

Screening Overview

Screening is the search for unrecognized disease in apparently healthy individuals using rapidly applied tests or examinations.
The goal is to identify disease early, allowing for earlier intervention and improved outcomes.
Screening aims to reduce mortality and suffering from disease.

Objectives of Screening

Introduce the concept of screening to students.
Explain the key difference between screening and diagnostic tests.
Outline the criteria for diseases suitable for screening and for effective screening tests.
Define sensitivity, specificity, predictive values (positive and negative).
Describe various types of screening.

Screening vs. Diagnostic Tests

Feature	Screening Test	Diagnostic Test
Target Group	Apparently healthy individuals	Individuals with symptoms or indications of illness
Application	Applied to groups	Applied to individual patients
Test results	Arbitrary and final	Modified based on new evidence, a sum of evidence
Criteria	Based on one criterion or cut-off point	Based on various symptoms, signs, and laboratory findings
Accuracy	Less accurate	More accurate
Cost	Less expensive	More expensive
Initiation	Initiated by investigator or agency providing care	Initiated by patient with a complaint

Definition

Screening is a test for a particular disease in asymptomatic individuals.

Possible Outcomes of Screening

Apparently healthy: (Screening tests)
Apparently normal: (Periodic re-screening)
Apparently abnormal:
Normal – periodic re-screening
Intermediate surveillance
Abnormal – treatment

Uses of Screening

Case detection
Disease control
Research purposes
Educational opportunities

Types of Screening

Mass/Population Screening: Screens an entire population without considering risk factors. Examples include:
Single disease screening (e.g., cervical cancer)
Multiphasic screening (e.g., biochemical profiles)
Selective/Targeted Screening: Screens individuals identified as being at high risk for the disease Examples include:
Single disease screening (e.g., CXR for pneumoconiosis)
Multiphasic screening (e.g., antenatal examinations)
Opportunistic Screening: Uses the opportunity to administer a screening test when an individual is already in contact with health services for another reason.

Criteria for Screening

Disease to be Screened:
Must be a significant health problem (high prevalence)
Have recognizable latent or early asymptomatic stages
Have an understood natural history of development from latent to symptomatic disease.
Must be detectable before symptoms/signs appear.
Required facilities should be available for confirmation of the diagnosis.
Effective treatment should exist.
Evidence that early detection and treatment reduces morbidity and mortality.
Expected benefits of early detection to outweigh risks and costs.
Screening Test to be Applied:
Acceptable to those screened
Repeatable results (reliability)
Intra-observer variation (within observer)
Inter-observer variation (between observers)
Biological (subject) variation:
Changes in observed parameters
Variations in patient perceptions/answers
Regression to the mean
Error relating to technical methods:
Defective equipment
Calibration errors
Faulty reagents
Inappropriately designed or unreliable tests.

Validity of Screening Tests

Validity (accuracy): The extent to which the test accurately measures what it is designed to. Measures whether those who have the disease are correctly identified and whether those who do not have the disease are correctly identified. Has two components:
Sensitivity and specificity.
Other factors including Simplicity, Safety, Rapidity, Low cost, and administration ease.
Sensitivity (SN): The ability to correctly identify those who have the disease. Calculated as (true positive/[true positive + false negative]) × 100 = TP.
Specificity (SP): The ability to correctly identify those who don't have the disease. Calculated as (true negative / [true negative + false positive]) × 100 = TN.
Predictive values:* Measure whether an individual actually has the disease given the results of the screening test.
Positive predictive value (PPV): Percentage of truly diseased people among those with positive test results calculated as (true positive / [true positive + false positive]) × 100.
Negative predictive value (NPV): Percentage of healthy people among those with negative test results calculated as (true negative / [true negative + false negative]) × 100.

Dependence and Calculation

True Positive (TP) is directly related to Sensitivity (SN).
False Negative (FN) is inversely related to Sensitivity (SN).
True Negative (TN) is directly related to Specificity (SP).
False Positive (FP) is inversely related to Specificity (SP).
Positive Predictive Value (PPV) depends on sensitivity, specificity, and prevalence of disease.
Negative Predictive Value (NPV) depends on sensitivity, specificity, and prevalence of disease.

Examples of Screening Programs

Childhood anemia screening
Cervical cancer screening

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Description

This quiz introduces the concept of screening and how it differs from diagnostic tests. It covers the criteria for effective screening and the key terms related to screening processes such as sensitivity and specificity. Test your knowledge on various types of screening aimed at improving health outcomes.