6: screening Flashcards by a m

define screening

A SYSTEMATIC attempt to DETECT an unrecognised
condition by the application of tests, examinations, or
other procedures, which can be applied RAPIDLY (and
cheaply) to DISTINGUISH between APPARENTLY well
persons who PROBABLY have a disease (or its precursor)
and those who probably DO NOT

How well did you know this?

Not at all

Perfectly

list the criterias for screening

Condition
Test
Intervention
Screening programme
Implementation

How well did you know this?

Not at all

Perfectly

list the criteria for implementation of a screening programme, including those relating to the condition (disease)

An IMPORTANT health problem (frequency/severity)
epidemiology, incidence, prevalence and natural history WELL UNDERSTOOD
cost-effective PRIMARY PREVENTION interventions must have been considered
must have EARLY DETECTABLE STAGE
psychological implications should be understood

How well did you know this?

Not at all

Perfectly

list the criteria for implementation of a screening programme, including those relating to the test

Simple, safe, precise and validated screening test
Agreed cut-off level must be defined and agreed
Acceptable to target population
Agreed policy on further diagnostic investigation for those who test positive and choices available to them
Distribution of results within population must be known

How well did you know this?

Not at all

Perfectly

list the criteria for implementation of a screening programme, including those relating to the treatment

Based on evidence
Early treatment must be advantageous
Clinical management and patient outcomes should be optimised

How well did you know this?

Not at all

Perfectly

list the criteria for implementation of a screening programme, including those relating to the programme

benefit should outweigh harm
facilities for screening / counselling / treatment
proven effectiveness (RCT data)
decision on perimeter should be scientifically justifiable to the public

How well did you know this?

Not at all

Perfectly

what are the difficulties of evaluating the effectiveness of screening programmes?

lead-time bias
length-time bias
selection bias

How well did you know this?

Not at all

Perfectly

what is lead-time bias?

early diagnosis falsely appear to prolong survival, but patient lives the same length of time

How well did you know this?

Not at all

Perfectly

what is length-time bias?

screening programmes are better at picking up slow-growing, unthreatening cases than aggressive, fast-growing ones
disease detectable through screening are more likely to have a favourable prognosis

How well did you know this?

Not at all

Perfectly

what is selection bias?

‘healthy volunteer effect’
• Studies of screening often skewed by ‘healthy volunteer’ effect
• Those who have regular screening likely to also do other things that protect them from disease

How well did you know this?

Not at all

Perfectly

how do you get rid of selection bias?

• An RCT would help deal with this bias

How well did you know this?

Not at all

Perfectly

list the criteria for implementation of a screening programme, including those relating to the implementation

• Clinical management and patient outcomes should be
optimised
• All other options for managing the condition should have been considered
• Management and monitoring programme – quality assurance
• Adequate staffing and facilities for programme
• Evidence-based information available to potential
participants (informed choice)
• Public pressure should be anticipated - decisions should be scientifically justifiable to the public

How well did you know this?

Not at all

Perfectly

what are the challenges of implementing a screening programme?

alters doctor-patient relationship
complexity of screening programmes need to be taken into account
evaluation of screening programmes difficult

How well did you know this?

Not at all

Perfectly

Difficulty in achieving informed choice in screening programmes?

• Communicating benefits, harms and risks of preventive

interventions can be challenging

How well did you know this?

Not at all

Perfectly

Sociological critiques of screening?

Structural critiques
Surveillance critiques
Moral obligation
Feminist critiques

How well did you know this?

Not at all

Perfectly

what are feminist critiques of screening?

screening is targeted more at women

How well did you know this?

Not at all

Perfectly

what are Surveillance critiques surrounding screening?

Study These Flashcards

Individuals and populations increasingly subject to

surveillance – prevention as social control?

what are structural critiques surrounding screening?

Study These Flashcards

Victim blaming / Individualising pathology

give examples of screening programmes in the UK

Study These Flashcards

BBC: breast, bowel, cervix
AAA (abdominal aortic aneurysm)
diabetic eyes
newborn spot blood test

what are the 2 types of errors that screening test will make?

Study These Flashcards

false positive

false negative

what is a false positive?

Study These Flashcards

refer well people for further investigation

what is a false negative?

Study These Flashcards

fail to refer people who do actually have an early form of the disease

what are the problems with referring well people for further investigation? (false positive)

Study These Flashcards

Put them through stress, anxiety, inconvenience
Direct costs
Opportunity costs

what are the problems of failing to refer people who do actually have an early form of the disease? (false negative)

Study These Flashcards

Inappropriate reassurance

* Possibly delay presentation with symptoms

what are the features of test validity?

* Sensitivity (detection rate) * Specificity * Positive predictive value * Negative predictive value

what is sensitivity of the test?

* The proportion of the people WITH the disease who are test POSITIVE * Also know as the DETECTION RATE * The proportion of the people who really have the disease who are identified correctly by the test as having the disease * the probability a case will test positive

how do you work out sensitivity of the test?

Sensitivity = True positives / (True positives + false negatives)

what does it mean if the sensitivity of the test is high?

• the test is very good at correctly identifying people with the disease you are screening for • A high sensitivity is ideal (although not always possible) (sensitive to disease)

what is specificity of the test?

• the proportion of the people WITHOUT the disease who are test NEGATIVE • The proportion of the people who really do not have the disease who are identified correctly by the test as not having the disease • Probability a non-case will test negative (specific to accuracy)

how do you work out specificity?

Specificity = True negatives / (false positives + true negatives)

what does a high specificity mean?

* the test is very good at correctly identifying people without the disease as not having the disease * A high specificity is ideal (although not always possible)

what should be expected if the same test is applied in the same way to different populations with regards to sensitivity and specificity? why?

• When the same test is applied in the same way in different populations the test will have the SAME sensitivity and specificity • Sensitivity and specificity are a function of the CHARACTERISTICS of the test

what is positive predictive value (PPV)?

Probability that someone who has tested POSITIVE actually HAS the disease “If I am test positive – what is my risk of actually having the disease?”

what is PPV strongly influenced by?

prevalence of the disease

how do you work out PPV?

PPV = True positives / (True positives + false positives)

what is the negative predictive value (NPV)?

the proportion of the people who are test negative who actually do not have the disease “If the screening test is negative – what are the chances that I really don’t have the disease?”

how do you work out NPV?

NPV = True negatives / (False negatives + True negatives)

what does a false positive result indicate?

patients MAY have the disease when in fact they do not

what are implications of false positive results?

• Patients will be offered (invasive) diagnostic testing with associated anxieties and risks – They will be turned into “patients” when they are not actually ill • May lead to lower uptake of screening in future • If the PPV is low there will be a lot of people with false positive results who undergo stress and unnecessary procedures

what does false negative indicate?

the screening test indicates that they do not have the disease when in fact they do

implications of false negative results?

• Patients will not be offered (invasive) diagnostic testing when in fact they may have benefited from it. Their disease, although present will not be diagnosed. • They will be falsely reassured – may present late with symptoms as a consequence

6: screening Flashcards

(41 cards)