Uses of screening test spm park book

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Uses of Screening Test

(Park's Textbook of Preventive and Social Medicine, p. 155-156)

Before listing the uses, it helps to understand the concept. Screening is defined as "the search for unrecognized disease or defect by means of rapidly applied tests, examinations or other procedures in apparently healthy individuals." It arises from the iceberg phenomenon of disease - the hidden submerged portion represents undiagnosed cases in the community that screening aims to detect.

Four Main Uses of Screening

a. Case Detection (Prescriptive Screening)

Defined as the presumptive identification of unrecognized disease, which does NOT arise from a patient's request.
People are screened primarily for their own benefit.
Examples of diseases sought: bacteriuria in pregnancy, breast cancer, cervical cancer, deafness in children, diabetes mellitus, iron deficiency anaemia, PKU (phenylketonuria), pulmonary tuberculosis, haemolytic disease of the newborn.
Example: neonatal screening.
Since disease detection is initiated by medical/public health personnel, they have a special obligation to ensure appropriate early treatment is started.

b. Control of Disease (Prospective Screening)

People are examined for the benefit of others (not just themselves).
Examples: screening of immigrants for tuberculosis and syphilis to protect the home population; screening for streptococcal infection to prevent rheumatic fever.
The screening programme, by leading to early diagnosis, allows more effective treatment and reduces the spread of infectious disease and/or mortality.

c. Research Purposes

Screening may be performed to obtain more basic knowledge about the natural history of diseases (especially chronic diseases like cancer, hypertension, where natural history is not fully known).
Initial screening provides a prevalence estimate; subsequent screening provides an incidence figure.
When done for research purposes, the investigator should inform study participants that no follow-up therapy will be available.

d. Educational Opportunities

Apart from benefits to individuals and public health information, screening programmes (e.g., screening for diabetes) provide:
- Opportunities for creating public awareness
- Educating health professionals

Key Distinction: Screening vs. Diagnostic Test

Screening Test	Diagnostic Test
Done on apparently healthy persons	Done on those with symptoms or sick
Applied to groups	Applied to single patients
Based on one criterion/cut-off point	Based on evaluation of symptoms, signs, and lab findings
Less accurate	More accurate
Less expensive	More expensive
Not a basis for treatment	Used as a basis for treatment
Initiative comes from the investigator/agency	Initiative comes from the patient with a complaint

Types of Screening (Bonus)

Since commonly asked alongside uses:

Mass screening - Screening of a whole population or sub-group, offered to all irrespective of individual risk (e.g., tuberculosis).
High-risk/Selective screening - Applied to high-risk groups defined by epidemiological research; most productive approach. Also includes screening for risk factors (e.g., serum cholesterol for CHD risk).
Multiphasic screening - Application of two or more screening tests in combination to a large number of people at one time (includes questionnaire, clinical exam, blood/urine tests, lung function, audiometry, visual acuity assessment).

Source: Park's Textbook of Preventive and Social Medicine (ISBN 9789382219163), Chapter on Epidemiology, pp. 155-156

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