screening test

Screening Test: Types Uses Validity And Evaluation

The search for unrecognized disease or defect by means of rapidly applied tests, examinations, or other procedures in an apparently healthy individual is known as screening.

Table of Contents

What is a screening test?

It is defined as “The search for unrecognized disease or defect by means of rapidly applied tests, examinations or other procedures in an apparently healthy individual.”

The main fundamental aspect behind the application of screening tests is the active search for diseases among apparently healthy people. It is to find the cases which present in the community as a submerged portion of the iceberg.

A screening test is usually applied before the onset of signs and symptoms in an individual.

The basic difference between screening tests and diagnostic tests is mentioned in table 1.

Screening TestDiagnostic Test
Applied in an apparently healthy individualApply in a symptomatic individual
​Applied in a group of peopleApplied to single
Test results are arbitrary and finalDiagnosis is not final
​Based on one criterion or cut of pointBased on signs and symptoms
​Less accurateMore accurate
​Less expensiveMore expensive
​Not form the basis for treatmentUsed as the basis for the treatment
The initiative comes from the investigator or agency providing careThe initiative come from a patient with a complaint
Screening vs Diagnostic test

Test The basic difference between the two tests you learned above

When is Screening Test Helpful?

It is not useful for diseases whose onset is quite obvious, there has to be considered a time lag between the onset of the disease and the usual time of diagnosis for the application of a screening test. If we can find the case early in apparently healthy and asymptomatic individuals by means of screening tests we can alter the final outcome.

It is differ from Periodic Health Examinations in the following aspects:

  • Capable of wide application.
  • Relatively inexpensive.
  • Requires less physician time, usually for interpretation.

A screening test is applied to only those conditions or diseases that follow the following criteria:

  • The condition should be an important healthcare problem (High prevalence).
  • There has to be a recognizable latent or long early asymptomatic period.
  • The natural history of the disease from the latent phase to the declared diagnosed phase has to be well understood.
  • A test needs to be available that can find the case before the onset of signs and symptoms.
  • Facilities should be available for the diagnosis of the condition.
  • Effective treatment should be available.
  • Good evidence needs to be available that suggests early detection and treatment reduce morbidity and mortality.
  • There should be an agreed policy concerning whom to treat as patients.
  • The expected benefits of early detection exceed the risk and cost.

Types: Screening Test

  1. Mass Screening

Applied to the whole population or a subgroup.

2. High-risk or selective

When it is applied to only high-risk or specific groups of people. For example, Ca.cervix is more common in lower socioeconomic classes so people belonging to a lower socioeconomic class are taken into consideration for the application of screening tests.

3. Multiphasic

Two or more tests simultaneously apply in a combination to a group of people for a single disease.

An Ideal test should be:

screening test characteristics
screening test characteristics

“Yield” is the amount of previously unrecognized diseases that are diagnosed as a result of screening efforts.

There are several ways we can check the validity of the screening test.

validity of the screening test

Evaluation of test:

Disease PresentDisease absentTotal
test positivea(True Positive)b(False Positive)a+b
test negative​c(False Negative)​d(True Negative)c+d
a+cb+da+b+c+d
screening test evaluation

1. Sensitivity: a / (a+c)*100

2. Specificity: d / (b+d)*100

3. Positive predicted value: a / (a+b)*100

4. Negative predicted value: d / (c+d)*100

5. Percentage of false negative: c / (a+c)*100

6. Percentage of false positives: b / (b+d)*100

Sensitivity: Ability of test to identify correctly all those who have the diseases (True Positive).

Specificity: Ability of a test to identify correctly all those who do not have a disease (True Negative).

Positive predictive value: Probability that the patient with the positive test result has the disease.

Negative predictive value: Probability that patient with negative test result does not has the disease.

False Negative: It means that the patient has the disease but the test comes negative.

False Positive: It means that the patient does not have the disease but the test comes positive.

Uses of screening tests:

  1. Case detection: This is also known as the “Prescriptive Type”. It is defined as the presumptive identification of unrecognized diseases. It is a very useful tool in epidemiology. Can be used to measure the disease burden in the community.
  2. Control of disease: This is also known as the “prospective type”. People are examined for the benefit of others.
  3. Research Purpose
  4. Educational opportunity

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FAQs

What is a screening test?

A screening test is a medical test that is used to identify individuals who may have a specific condition or disease, even if they do not have any symptoms. These tests are used to detect potential health problems early, when they may be more easily treated or managed.

What types of screening tests are available?

There are many different types of screening tests available, including blood tests, urine tests, imaging tests, and genetic tests. Some common examples include mammograms for breast cancer, colonoscopies for colon cancer, and Pap tests for cervical cancer.

Who should get screened?

The specific screening tests that are recommended for an individual will depend on their age, gender, family history, and overall health. It is important to speak with a healthcare provider to determine which tests are appropriate for you.

What are the benefits of screening tests?

Screening tests can help detect potential health problems early, when they may be more easily treated or managed. This can lead to better outcomes and a higher quality of life. Additionally, screening tests can help individuals take steps to prevent certain conditions from developing in the first place.

Are there any risks associated with screening tests?

Some screening tests may have risks associated with them, such as discomfort or pain during the test, or false positive results. It is important to discuss any potential risks with a healthcare provider before undergoing a screening test.

How often should I get screened?

The frequency with which you should get screened will depend on the specific test and your individual health needs. It is important to speak with a healthcare provider to determine how often you should be screened.

How accurate are screening tests?

The accuracy of a screening test will depend on the specific test and the individual being screened. Some tests have a high rate of accuracy, while others may be less reliable. It is important to discuss the accuracy of a specific test with a healthcare provider before undergoing it.

What should I do if my screening test comes back positive?

If your screening test comes back positive, it is important to speak with a healthcare provider to determine next steps. Additional testing, such as a diagnostic test, may be needed to confirm a diagnosis.

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