WEEK 2: Workshop: Screening Programmes Flashcards
What is screening?
It is the application of a test or procedure to asymptomatic people in order to detect disease early.
Screening classifies people into 2 groups. State them.
It classifies people into 2 groups:
*One at high risk of developing clinical disease
*The other at low risk of developing it.
What is the aim of screening?
*To detect disease early, before it becomes clinically apparent, and treat it
State the 3 Assumptions in Screening
- Early detection before the development of symptoms means a better prognosis
- Treatment - effective, acceptable and available
- Relies on screening tests
State the Benefits of Screening.
■ Early disease identification in the community
■ Results in early intervention (prevention or control)
■ Hopes to reduce disease morbidity or/and mortality
Differentiate Screening vs Diagnosis.
■ In screening, the patient being screened is asymptomatic and at apparently low risk of the disease being screened for
■ In diagnosis, the patient has symptoms or signs indicating a high likelihood of the disease being tested for
Differentiate between screening and diagnostic tests. (6)
Screening Test
■ Done on apparently healthy individuals
■ Applied to groups
■ Based on one criteria & cutoff
■ Less accurate
■ Less expensive
■ Not a basis for treatment
Diagnostic test
■ Done on sick or ill individuals
■ Applied on single patients
■ Based on evaluation of signs/symptoms & lab findings
■ More accurate
■ More expensive
■ Used as basis for treatment
Which of the following are screening tests?
■ Urine dipstick
■ Viral Load in HIV
■ CD4 Count in HIV
■ Random blood glucose
■ Fasting blood glucose
■ Mammogram
■ Renal biopsy
■ PAP SMEAR
■ COVID TEST- PCR
■ DIGITAL RECTAL EXAM (DRE)
Screening Tests:
*Urine dipstick
*Viral Load in HIV
*CD4 Count in HIV
*Random blood glucose
*Fasting blood glucose
*Mammogram
■ PAP SMEAR
■ COVID TEST- PCR
■ DIGITAL RECTAL EXAM (DRE)
Non-Screening Test:
*Renal biopsy
State the Principles of Screening. What is considered?
■ The choice of disease for which to screen
■ The nature of the screening test
■ The availability of a treatment for the disease
■ The relative costs of the screening
What elements of the disease are considered?
The Disease
■ The condition should be an important public health problem
■ There should be a recognizable latent or early symptomatic phase
■ The natural history of the disease should be adequately known & understood
What is the natural history of a disease?
The natural history of a disease refers to the course or progression of a medical condition in the absence of treatment.
It outlines the typical development of the disease over time, from the initial exposure or onset of the disease to its resolution, chronicity, or death.
State the principles of the test which are considered.
■ There should be an appropriate test available for detection of the disease
■ The screening test should be valid, reliable, with acceptable yield
■ The test should be acceptable to the population
What principles of the treatment should be considered.
■ There should be an effective treatment available for the disease
■ There should be adequate facilities for diagnosis and treatment of the disease
■ There should be an agreed policy on who to treat
State the principles of cost which are considered.
■ The cost of case-finding (including a diagnosis and treatment of patients diagnosed) should be economically balanced in relation to possible
expenditure on medical care as a whole
■ Case finding should be a continuing process and not a “once off” project
State the Criteria for evaluating a screening test.
■ Validity (accuracy): How close is the result of a test to its true value (sensitivity & specificity)
■ Yield: Amount of disease detected in the population, relative to the effort
■ Reliability (precision): How close are the results of a test on repetition
What is used to assess the validity of a screening test in establishing the presence of disease we compare with a gold standard?
Sensitivity and specificity
Define sensitivity and specificity.
■ Sensitivity: The ability of a test to correctly identify those who have the disease (TP)
■ Specificity: The ability of a test to correctly identify those who do not have the disease (TN)
What is yield?
Define Predictive Value of a Positive Test (PPV) and Predictive Value of a Negative Test (NPV)
Yield: Predictive Value
■ Relationship between Sensitivity, Specificity, and Prevalence of Disease
■ Predictive Value of a Positive Test (PPV): Likelihood that a person with a positive test has the disease
■ Predictive Value of a Negative Test (NPV): Likelihood that a person with a negative test does not have the disease
State the formula for calculating the predictive value of a positive and negative test respectively.
PPV= True Positives/ All positives
NPV= True Negatives/ All negatives
PPV, Sensitivity, Specificity and Prevalence
Define reliability.
Reliability
■ The ability of a test to give consistent results when performed more than once on the same individual under the same conditions
■ Reliability does not ensure validity, but lack of reliability constrains validity.
Repeatability
■ Get same result
■ Each time
■ From each instrument
■ From each rater
SCREENING Programmes not just tests…
A screening programme consists of all those activities from the identification of the population likely to benefit right through to definitive diagnosis and treatment.
Can be opportunistic: offer of a test for an unsuspected disorder at a time when a person presents to the health worker for another reason –e.g. hypertension, cholesterol, glycosuria.
State aims of a screening programme.
■ To identify those individuals who are
– more likely to be helped than harmed by further tests
– Whom treatment will reduce the risk of a disease or its complications
Criteria for a screening Programme adapted from
Wilson & Junger.
State them.
Criteria for a screening Programme adapted from
Wilson & Junger
■ The condition (disease) should be an important health problem
– Severity
– Prevalence
■ The natural history of the condition should be understood
■ There should be a recognizable latent or early symptomatic stage amenable to
treatment
■ There should be a valid screening test
– Acceptable
– Sensitivity
– Specificity
■ There should be an accepted treatment recognized for the disease
■ Treatment should be more effective if started early
■ There should be a policy on who should be screened and treated
■ Diagnosis and treatment should be cost-effective
■ Case-finding should be a continuous process
■ What is known already about participation in screening for this disease?
■ Are those most at risk likely to attend?
Costs of a screening programme.
State the costs involved.
What are some of the savings involved?
■ Direct and indirect
■ This includes the costs of :
– The screening and confirmatory tests
– All staff involved – collection, laboratory, analysis, admin [to call and recall]
– Treatment costs [may be surgery, radiotherapy etc]
– Psychosocial costs
■ Savings include
– prevention of serious illness
– savings from lost work time
– value of pain and suffering
prevented must be balanced
against suffering caused by being
given a false positive result, or
waiting for confirmation
State examples of screening programmes in clinical practice.
Examples of screening programmes in clinical practice
* Diabetes – for the disease and for the consequences of the disease e.g. retinopathy
* Cancers – breast, cervical, prostate
* Sexually transmitted infections – HIV, Chlamydia, syphilis
* School health – hearing, vision etc.
* Lifestyle screening in general practice – smoking, alcohol
* Genetic Screening
* Pre-employment screening
Evaluating a screening programme
* Is it effective in reducing mortality and morbidity from the disease ?
* What is the end point?
- Provision of back up preventive counselling often deficient.
Evaluating a screening programme
* Is it effective in reducing mortality and morbidity from the disease?
What is the end point?
* prevention of death from cancer?
* Or prevention of infertility with Chlamydia screening – long time delay to
benefit.
* Short term reductions in prevalence may be associated with reduced duration
of infection rather than reduced incidence of disease.
* Contact tracing
- Provision of back up preventive counselling often deficient.
Ethical aspects of screening
State the 4 ethical principles.
■ Screening programs have the potential to violate each of these
Ethical aspects of screening
■ Consists of four principles:
– Beneficence,
– Non-maleficence,
– Justice
– Autonomy
■ Screening programs have the potential to violate each of these
State the potential harm of the following ethical principles in screening.
– Beneficence,
– Non-maleficence,
– Justice
– Autonomy
– Beneficence:
*Screening programs may a large benefit at a population level for those who can be offered treatment early but no impact of individual risk
– Non-maleficence
*Psychological harm from false negatives in interval before diagnostic testing.
*Preventable death resulting from false negative test results
*Iatrogenic harm from subsequent diagnostic testing (which is invasive)
*Unwarranted reassurance from false negatives may cause people to ignore symptoms that develop later
– Justice
*Deprived, vulnerable people at greater risk of disease are likely to undergo screening
*A challenge for screening programs is to ensure equality in uptake and linkage into care.
*Screening programs can increase the health gap
– Autonomy
*Enthusiastic clinicians and publicity campaigns coerce patients into screening.
*The physician has to balance non-maleficence and patient autonomy.
Social Aspects of screening.
State factors that may increase participation in screening.
*Knowledge of condition
*Perception of susceptibility
*Perception of disease severity
*Knowledge of availability of treatment
State factors that may decrease participation in screening.
*Disease phobia
*Stigma associated with the condition
*Unpleasant diagnostic tests and treatment
*Socio-economic factors (income, education, deprivation, employment.)
*Socio-demographic factors (age, sex, ethnicity, language, creed)
*Accessibility of screening sites
State the limitations of screening.
Limitations
■ Screening can involve cost and use of medical resources on a majority of people who do not need treatment.
■ Adverse effects of screening procedure (e.g. stress and anxiety, discomfort, radiation exposure, chemical exposure).
■ Stress and anxiety caused by a false positive screening result.
■ Unnecessary investigation and treatment of false positive results.
■ Stress and anxiety caused by prolonging knowledge of an illness without any improvement in outcome.
■ A false sense of security caused by false negatives, which may delay final
diagnosis
