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Screening methods


Screening methods Dr K N Prasad Community Medicine Diseases are having iceberg phenomenon Screening is the early detection of disease precursors to disease. – PowerPoint PPT presentation

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Title: Screening methods

Screening methods
  • Dr K N Prasad
  • Community Medicine

  • 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
  • Tests
  • Questions
  • 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
  • The screening procedure itself does not diagnose
    the illness.
  • Screening test will need further evaluation with
    subsequent diagnostic tests or procedures.

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  • 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

Final critical point
Usual time of diagnosis
Disease onset
First possible detection
Screening time
Lead time
Lead time is the period between diagnosis by
early detection and diagnosis by other means
Screening pathways
  • Healthy
  • Disease or precursor
  • Detectable
  • Symptoms develop
  • Advance disease
  • Death

Screening possible Intervention to avert
disease development or its consequences Life
  • 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
  • Examinations
  • Pap smear, Mammogram, Clinical breast exam, Blood
    pressure determination, Cholesterol level, Eye
    examination/vision test, and Urinalysis.

Uses of screening tests
  1. Cases detection (Prescriptive )
  2. Screened primarily for their own benefit Ex.
    Neonatal, cancers
  3. Control of diseases (Prospective)
  4. Screened for benefit of others
  5. Ex. STD, TB
  6. Research purpose
  7. May aid in obtaining basic knowledge about
    natural history of disease
  8. Education opportunity
  9. To create public awareness and educating health

Types of screening
  1. Mass screening
  2. Screening afford to all irrespective of the
    particular risk Ex. TB
  3. High risk or selection screening
  4. Applied to selective high risk group on the basis
    of epidemiological research
  5. Ex. Cervical Cancer, heart diseases
  6. Multi purpose screening
  7. Application of two or more tests in combination
    to a large number at one time
  8. Ex. Questionnaire, examination, laboratory tests

Criteria for population based screening
  1. Knowledge of disease
  2. Condition must be an important problem
  3. Presence of recognisable latent or early
    symptomatic stage
  4. Natural history of the condition must be
    adequately understood
  5. Feasibility of screening procedures
  6. Suitable test or examination
  7. Acceptable to the population
  8. Should be a continuous process

  • Diagnosis and treatment
  • acceptable treatment with recognisable disease
  • Facilities for diagnosis treatment should be
  • agreed upon policy to treat as patients
  • Cost considerations
  • adequate resources
  • Expected benefit

  1. Condition should be an important public health
  2. There should be a recognizable early or latent
  3. There should be an accepted treatment for persons
    with condition
  4. The screening test is valid, reliable and
    acceptable yield
  5. The test should be acceptable to the population
    to be screened
  6. The cost of screening and case finding should be
    economically balanced in relation to medical care
    as a whole

Screening tests
  • Acceptability
  • Simple, minimum pain or discomfort, easy, safety,
    rapidity , acceptable procedure, etc.
  • Repeatability
  • Must give consistent result when repeated several
    times on the same subject or individual
  • Observer variation
  • Biological variation

Observer variation
  • Intra 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
  • Differences in measurements on the same (
    subject or material) by different investigators
  • Ex. X ray, blood smears, organisms, etc..

Biological variation
  • Variation in physiological variables. Ex. BP,
    Rates, etc.
  • Changes in parameters observed
  • Ex. MI, Cancers, etc
  • Variations in their symptoms /signs
  • Memory, pain, quality of care, etc.
  • Regression to the mean
  • 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.

Thank you
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  • Screening test is intended for initial
  • Diagnosis involves confirmation of presence or
    absence of disease in someone suspected or at
    risk for having a disease.
  • Case finding measures