Screening tests are used to identify individuals at risk for a disease who are apparently well, sorting them from those who do not have risk factors. The main elements of an effective screening program are that it targets a disease with significant burden and effective treatment, uses a valid, precise, low-cost and low-risk screening test, and screens a population with high disease prevalence and compliance with follow-up testing and treatment. Examples of common screening tests include mammography, fecal occult blood tests, and Pap smears. Screening can be mass screening of all individuals or selective based on factors like age and sex. The goal of screening is to diagnose disease earlier through a series of tests.

1. Screening terminology
Dr. Ibrahim Saied
Epidemiology Consultant
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2. Different kinds of testing in medicine
•“Diagnostic” - specifically looking for a suspected
condition which is tested for and confirmed or
excluded
•“Case-finding” - usually in an investigation of
exposed people, to sort the exposed and ill from
the exposed and well. (During outbreaks)
•“Screening” - usually no specific exposure or
indication that the individual has disease
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3. 3
Introduction
• Diagnostic test
• Screening test
• Screening is an attempt to diagnose the disease
earlier when it is curable.
• Not all diagnostic tests can be used as a screening tool

4. 4
Screening and Diagnosis
• Primary purpose of screening is to identify individuals at
RISK for disease
• Screening tests sort out apparently well persons who
 have a disease
Or have a risk factor for disease
from those who do not
• Screening tests are not intended to be diagnostic

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Main elements of screening program
• The screened disease (with country priority)
• The proposed screening test (well chosen)
• The population to which the screening program will
be done (well defined)

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Screening in health care / the disease
•The disease
• Significant burden (morbidity and mortality)
• Acceptable, available and effective treatment
• A relatively enough pre-symptomatic period
• A better outcome with early intervention

7. 7
Screening in health care / the test
•The test
• Valid = Good sensitivity and specificity
• Precise = reliable = reproducible = repeatable
• Low cost, inexpensive.
• Low risk
• Availability of confirmatory tests

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•The population (to which the screening
program will be done)
• High prevalence of the disease
• High compliance with the test and with
subsequent tests and treatments
• Sense of vulnerable
Screening in health care / the population

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Examples of screening tests:
• Hypothyroidism and hearing loss in newborns
• Mammography for breast cancer
• Occult fecal blood for colorectal cancers
• Cervical Pap smear for cervical cancer
• Specific screening tests for mental problems:
e.g., addiction and depression

10. Types of screening
• Mass screening, no selection of population (e.g., checking all infants
for hearing problems)
• Selective screening (e.g., by age and sex: mammograms for women
aged over 40)
• Multiphase screening (a series of tests, as family doctors do at annual
health exams)
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11. Logic of screening
Apparently well population
Screening test
Negative results
Positive results:
Diagnostic test
Disease No disease
Disease No disease
(False negative) (True negative) (True positive) (False positive)
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