Screening methods

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Screening methods

• Dr K N Prasad
• Community Medicine

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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
• Tests
• Questions
• Examinations
• Laboratory tests
• X rays

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• 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.

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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

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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
outcome
A
Screening time
B
Lead time
Lead time is the period between diagnosis by
early detection and diagnosis by other means
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Screening pathways

• Healthy
• Disease or precursor
• Detectable
• Symptoms develop
• Advance disease
• Death

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

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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
   professionals

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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
   etc.

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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

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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

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Principles

1. Condition should be an important public health
   problem
2. There should be a recognizable early or latent
   stage
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

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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

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

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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

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Thought for the day

• Every job is a self portrait of the person who
  did it.
• Autograph your work with excellence.

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Thank you
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Difference

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