This document discusses screening, including defining screening as applying tests to asymptomatic individuals to identify those at high risk of disease. It outlines objectives of screening like early disease detection. Characteristics of diseases suitable for screening include having a long pre-symptomatic phase and effective treatment existing. Screening tests should be reliable, acceptable, safe and low-cost. Sensitivity measures a test's ability to correctly identify those with disease, while specificity measures its ability to correctly identify those without disease. Screening criteria include the disease burden and test validity, reliability, costs and benefits.

1. ScreeningScreening
Dr. Maha MoemenDr. Maha Moemen

2. • Learning objectives:
• 1- To identify the concept and objectives
of screening.
• 2-To identify characteristics of disease
suitable for screening.
• 3- to be able to calculate screening test
characteristics as sensitivity and
specificity.

3. • Definition:
It is the application of a test or procedure
to asymptomatic ,apparently well
individuals to separate those with high
probability of having or developing a
disease from those with a low probability
of having or developing the disease.
Those identified as likely to have the
condition will undergo further diagnostic
procedure.

4. • Periodic examination & screening:
• Capable of wide application.
• Apply relatively inexpensive tools.
• Require little physician time.
• Applied to those who don`t attend health
care facility.

5. Screening and case finding:
Case finding is the use of clinical ,laboratory
or non-lab test to detect disease in
individuals seeking medical care for other
reasons.
e.g. detection of TB in patient suffering from
hypertention.

6. Screening and diagnosis:
• The purpose of screening is to segregate
those who may have the condition .it is an
initial step , it needs confirmation.
• Diagnosis is a procedure to confirm or
disprove the existence of a disease or
abnormality.

7. Screening test Diagnostic test
Done to those apparently
healthy
Done to those with suggestive
signs and symptoms
Applied to a group of individuals Applied to a single person
Results are based on one
criteria
Results are based on the
evaluation of a number of
symptoms, signs and
investigation.
Results are not conclusive Results are conclusive and final
Less accurate More accurate
Less expensive More expensive
Not a base for treatment Basis for trearment

8. Concept and objectives ofConcept and objectives of
screeningscreening
• The goal of screening is to identify
affected individuals before onset of
symptoms so that action can be applied to
reduce risk of developing clinical disease
(i.e reduce morbidity) and severity or
death due to the disease (i.e.to improve
the outcome)

9. Uses of screeningUses of screening
1-Case detection:
To identify unrecognized disease which does not
arise from the patient request.
2-control of disease:
To prevent transmission of the disease to healthy
community members.
3-Research purpose:
To estimate the prevalence of a disease and
subsequent screening will provide data on the
incidence.

10. Types of screeningTypes of screening
•1-Mass screening:
•Application of the screening program to the
whole population or population subgroup as
adults, children ,industrial workers.
•2-High risk or selective screening;
•The screening program will be applied to a
selective group of population who are at a high
risk e.g. cancer cervix in low social class.

11. Criteria for effective screeningCriteria for effective screening::
•1-Characteristics of a disease suitable for
screening:
1-the disease should be a major public health
problem for the individual or community and
should have a serious consequences as human
suffering or death.
2-The disease should have a reasonably long
and /or detectable pre-symptomatic (pre-clinical)
phase.

12. • 3- The disease should have a high
prevalent among screened population.
• 4-there should be a suitable screening test
available ,that can detect the disease or
the defect prior to the signs and
symptoms.
• 5-There is a good evidence that early
detection reduces morbidity and mortality.
• 6-Facilities should be available for the
confirmation of the diagnosis.

13. •7-There should be an effective and
acceptable treatment for the disease if
identified in an early stage, as it is
unreasonable to screen for disease with
no available treatment.
•8-The expected benefit of early detection
out weight the risks and the cost.

14. Characteristics of ideal screeningCharacteristics of ideal screening
testtest
A) Reliability:
Does the test give the same result when repeated
applications are made on the same individual?
B) Acceptability
C) Safety
D) Cost:
1-cost of applying the test itself.
2-cost of performing additional tests on people with
false positive to correct the test's mistakes.

15. ValidityValidity
To what extent the test accurately measures
which it suppose to measure.
OR The ability of the test to separate or
distinguish those who have the disease
from those who have not.
e.g. glucosuria for diabetes, more valid or
accurate is glucose tolerance curve.

16. Validity :sensitivity&specificityValidity :sensitivity&specificity
Does the screening test accurately indicate
the presence or absence of the disease or
pre-disease state?
“True” disease status is determined by the
most definitive diagnostic method, referred
to as a “gold standard”.
Sensitivity and specificity are used to
describe the performance of the screening
test relative to the true disease status.

17. Format for comparison of results of aFormat for comparison of results of a
diagnostic test against the true diseasediagnostic test against the true disease
statusstatus
Screening
test
Disease No disease Total
Positive True
positive (A(
False
positive (B(
A+B
Negative False
negative (c(
True
Negative
(D(
C+D
Total A+C B+D A+B+C+D

18. SensitivitySensitivity
It is the percentage of persons with the disease of
interest who have positive test results i.e. it is
the ability of the test to identify correctly those
who truly have the disease.
Sensitivity=True positive/true positive+false
negative x100
Sensitivity=a/a+c x100

19. SpecificitySpecificity
Specifity is the percentage of persons
without the disease of interest who have
negative test results.
i.e. the ability of the test to identify correctly
those who truly does not have the
disease.
Specifity =true negative/true negative+false
positive
Specifity = D/D+Bx100

20. Prevalence=A+C/ A+B+C+D x100
Positive predictive value=it is the percentage of
persons with positive test results who actually
have the disease of interest.
PV=a / a+b x100
Negative predictive value: is the percentage of
persons with negative test results who actually
do not have the disease of interest.
Negative predictive value=D / D+C x 100