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Diseases are having iceberg phenomenon
Screening is the early detection of disease precursors to disease. Or susceptibility to diseases in individuals who do not show any signs of the disease
TestsQuestions
Examinations
Laboratory tests
X rays
Definition: “The PRESUMPTIVE identification of UNRECOGNIZED disease or defect by the application of tests, exams or other procedures which can be applied RAPIDLY to sort out apparently well persons who PROBABLY have a disease from those who PROBABLY do not.”
Screening refers to the application of a medical procedure or test to people who as yet have no symptoms of a particular disease, for the purpose of determining their likelihood of having the disease.
The screening procedure itself does not diagnose the illness.
Screening test will need further evaluation with subsequent diagnostic tests or procedures.
Differences Screening test Done on apparently
healthy Applied to groups Based on one or cut off
criteria Less accurate Not a basis for treatment Initiative comes from the
health agency
Diagnostic test Done on those with sick
or indications Applied to single patient Based on evaluation of
number of symptoms, signs or lab tests
More accurate Basis for treatment Initiative comes from
patient with complaint
Lead time concept
• Time lag present between disease onset and usual time of diagnosis
Disease onset
First possible detection
Final critical point
Usual time ofdiagnosis outcome
Screening time
Lead time
A
B
Lead time is the period between diagnosis by early detection and diagnosis by other means
Screening pathwaysHealthy
Disease or precursorDetectable
Symptoms develop
Advance disease
Death
Screening possible
Intervention to avert disease development or its consequences
Life prolonged
Objective The goal of screening is to reduce morbidity or
mortality from the disease by detecting diseases in their earliest stages, when treatment is usually more successful.
Sort out the population who has risk from others
ExaminationsPap smear, Mammogram, Clinical breast exam, Blood
pressure determination, Cholesterol level, Eye examination/vision test, and Urinalysis.
Uses of screening tests1. Cases detection (Prescriptive )
1. Screened primarily for their own benefit Ex. Neonatal, cancers
2. Control of diseases (Prospective)1. Screened for benefit of others 2. Ex. STD, TB
3. Research purpose1. May aid in obtaining basic knowledge about
natural history of disease4. Education opportunity
1. To create public awareness and educating health professionals
Types of screening1. Mass screening
1. Screening afford to all irrespective of the particular risk Ex. TB
2. High risk or selection screening1. Applied to selective high risk group on the
basis of epidemiological research2. Ex. Cervical Cancer, heart diseases
3. Multi purpose screening1. Application of two or more tests in
combination to a large number at one time2. Ex. Questionnaire, examination, laboratory
tests etc.
Criteria for population based screening
1. Knowledge of disease1. Condition must be an important problem
2. Presence of recognisable latent or early symptomatic stage
3. Natural history of the condition must be adequately understood
2. Feasibility of screening procedures1. Suitable test or examination
2. Acceptable to the population
3. Should be a continuous process
Contd. Diagnosis and treatment acceptable treatment with recognisable
disease Facilities for diagnosis & treatment should be
available agreed upon policy to treat as patients
Cost considerations adequate resources Expected benefit
Principles 1. Condition should be an important public health
problem2. There should be a recognizable early or latent
stage3. There should be an accepted treatment for
persons with condition4. The screening test is valid, reliable and acceptable
yield5. The test should be acceptable to the population to
be screened6. The cost of screening and case finding should be
economically balanced in relation to medical care as a whole
Screening testsAcceptability :
Simple, minimum pain or discomfort, easy, safety, rapidity , acceptable procedure, etc.
RepeatabilityMust give consistent result when repeated
several times on the same subject or individual
Observer variationBiological variation
Observer variationIntra observer or within observer variation
Measurements should be same( subject or material) if recorded several times at that time or event
Ex. Ht, wt, lab tests. etc..
Inter observer variation or between observer variationDifferences in measurements on the same
( subject or material) by different investigatorsEx. X ray, blood smears, organisms, etc..
Biological variation1. Variation in physiological variables. Ex. BP,
Rates, etc.
2. Changes in parameters observed1. Ex. MI, Cancers, etc
3. Variations in their symptoms /signs1. Memory, pain, quality of care, etc.
4. Regression to the mean1. Tendency of values merge at the mean.
This is tested by repeated observation over time
Thought for the day
Every job is a self portrait of the person who did it.
Autograph your work with excellence.