HaDSoc Week 6

Question 1

Define diagnosis

Answer 1

The definitive identification of a suspected disease or defect by application of tests, examinations or other procedures (which can be extensive) to definitely label people as either having a disease or not having a disease

Question 2

Give three methods for detection of disease

Answer 2

Spontaneous presentation
Opportunistic case finding
Screening

Question 3

What is spontaneous presentation?

Answer 3

Person presents with symptoms - self-defined as ‘patient’
To GP, A+E, other services
Diagnosis made

Question 4

What is opportunistic case finding?

Answer 4

Person presents with symptoms related to particular disease/problem
Health professional takes the opportunity to check for other potential conditions:
BP, urine dipstick

Question 5

Describe the process of diagnosis

Answer 5

Presentation
History, examinations, investigations
Either has the disease or doesnt
Treatment follows
Patient willing to accept reasonable risk of side effects in order to get well

Question 6

Define screening

Answer 6

A systematic attempt to detect an unrecognised/asymptomatic condition by the application of tests, examinations, or other procedures, which can be applied rapidly (and cheaply) to distinguish between apparently well persons of an identified high risk population, who probably have a disease (or its precursor) and those who probably do not. The screening provider then offers information, further tests and treatment. This is to reduce associated risks or complications.

Question 7

Describe the process of screening

Answer 7

Rapid/cheap test used on an appropriate population to identify high risk and low risk individuals for a particular condition.
Those that are identified as being high risk are then offered diagnostic tests which either show presence of disease or no disease.
The individuals identified as having the disease are then offered further information and treatment

Question 8

What is the purpose of screening?

Answer 8

Give a better outcome compared with finding something in the usual way (having symptoms and self-reporting to health services)
In other words, if the outcome of screening is the same as when treatment is given at the time of symptom presentation, then there is no point in screening
Finding something earlier not the primary objective

Question 9

Give some example of population screening programmes that run in the UK

Answer 9

Abdominal aortic aneurysm
Bowel cancer screening
Breast screening programme
Cervical screening programme
Diabetic eye screening programme
Foetal anomaly screening programme
Infectious disease in pregnancy screening programme
Newborn and infant physical examination screening programme
Newborn blood spot screening programme
Newborn hearing screening programme
Sickle cell and thalassaemia screening programme

Question 10

Give some examples of conditions which there are no screening programmes and why this might be controversial

Answer 10

Prostate cancer (PSA)
Breast cancer screening <50 years of age (except those in pilot study)
Cervical cancer <25 years of age

Public pressure - if someone is affected by a condition they may have trouble understanding why we dont screen for it - can only see it from their perspective

Question 11

What are the UK National screening committee criteria for deciding if there should be a screening programme for a condition/disease?

Answer 11

Condition
Test 
Intervention
Screening programme
Implementation

Question 12

What is meant by the national screening committee criterion, ‘condition’ ?

Answer 12

The condition has to be important in terms of frequency, severity - with epidemiology, incidence, prevalence and natural history being understood - have to know the difference that screening would make
All the cost-effective primary prevention interventions should have been implemented as far as practicable
If the carriers of a mutation are identified as a result of screening the natural history of people with this status should be understood, including the psychological implications

Question 13

What is meant by the national screening committee criterion, ‘test’?

Answer 13

Has to be simple and safe as they are asymptomatic - cant expose to unacceptable risks
Has to be a precise and validated screening test - need to trust the data it is giving you
Distribution of test values in the population must be known and an
agreed cut-off level must be defined and agreed - when should and shouldnt intervene
Acceptable to target population - e.g. Is the test invasive - what are the benefits v.s. The risks
Agreed policy on further diagnostic investigation of those who test
positive and choices available to them
If the test is for a particular mutation or set of genetic variants the
method for their selection and the means through which these will be
kept under review in the programme should be clearly set out

Question 14

What are the consequences of false positives?

Answer 14

Put the individual through stress, anxiety, inconvenience
Turned into patients when not actually ill
Invasive diagnostic tests - risks
Direct costs - staff, services
Opportunity costs - money that could be spent somewhere else
Lower uptake of screening in future –> greater risk of interval cancer
Low PPV –> lots of false positives

Question 15

What are the consequences of false negatives?

Answer 15

Inappropriate reassurance
Possibly delay presentation with symptoms - because they’ve been told they are fine so will dismiss the condition as an option
Not offered diagnostic test when may have benefited from it

Question 16

What are the features of test validity?

Answer 16

Sensitivity
Specificity
Positive predictive value
Negative predictive value

Question 17

What is sensitivity defined as?

Answer 17

The proportion of people who have the disease who will be correctly identified as having the disease (receive a positive result)
Also known as detection rate

Question 18

How is sensitivity calculated ?

Answer 18

People with the disease who tested positive (true positives) / total number of people with the disease (true positives + false negatives)

Question 19

What does sensitivity mean?

Answer 19

If the sensitivity is high then 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)

Question 20

What is specificity ?

Answer 20

The proportion of people who do not have the disease who are correctly identified as not having the disease (test negative)

Question 21

How is specificity calculated?

Answer 21

Number of people without the disease who were correctly identified as not having the disease (true negatives)/ Total number of people without the disease (true negatives + false positives)

Question 22

What does specificity mean?

Answer 22

If the specificity is high then 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)

Question 23

What are the features of sensitivity and specificty?

Answer 23

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

Question 24

What is the positive predictive value?

Answer 24

The probability that someone who was identified as having the disease/tested positive for the disease actually has the disease
This is strongly influenced by the prevalence of the disease

Question 25

How is the positive predictive value calculated?

Answer 25

The number of people identified as having the disease (tested positive) who actually have the disease (true positives) / The total number of people who were identified as having the disease (tested positive) (true positives + false positives)

Question 26

What is the reason for considering carefully what population to screen ?

Answer 26

The prevalence of the condition affects the PPV
If the prevalence is high then the PPV will be high
If the prevalence is low than the PPV will be low e.g. More false positives will occur

Question 27

What is the negative predictive value?

Answer 27

The proportion of people identified as not having the disease (tested negative) who actually do not have the disease

Question 28

How is the negative predictive value calculated?

Answer 28

Number of people identified as not having the disease (tested negative) who actually do not have the disease (true negatives)/ The total number of people who were identified as not having the disease (true negatives + false negatives)

Question 29

What is the meaning of the national screening committee criterion, ‘intervention’?

Answer 29

Have to have an effective intervention for those identified through screening - have to have evidence that it improves outcome compared with people who present at symptomatic phase (usual care)
There should be agreed evidence based policies covering which individuals should be offered interventions and the appropriate intervention to be offered.

Question 30

What is meant by the national screening committee criterion, ‘screening programme’?

Answer 30

Proven effectiveness in reducing mortality or morbidity (high quality RCT data)
Evidence that the complete screening programme is clinically, socially and ethically acceptable to health professionals and public
Benefit gained by individuals should outweigh any harms for example from overdiagnosis, overtreatment, false positives, false reassurance, uncertain findings and complications
Opportunity cost of the screening programme should be economically balanced in relation to expenditure on medical care as a whole

Question 31

What is meant by the national screening committee criterion, ‘implementation’?

Answer 31

Clinical management and patient outcomes should be optimised in all healthcare providers
All other options for managing the condition should have been considered
Management and monitoring programme – quality assurance (e.g. Accuracy of results, how long it takes to get results etc.)
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

Question 32

What are some questions and debates concerning screening?

Answer 32

Is the natural history always understood?
How many abnormalities would regress spontaneously or never be problematic? E.g. Older men dying with prostate cancer rather than of prostate cancer
Are the ‘right’ people being screened? E.g. Hypochondriacs likely to attend lots of screening, have healthy behaviours etc. Also need to make sure screening a population where the PPV/ prevalence is as high as possible
Has screening caused any observed reduction in mortality?
Over-diagnosis and over-treatment?
Psychological impact?

Question 33

Why should screening programmes be evaluated?

Answer 33

Must be based on good quality evidence
Pressure from public e.g. Prostate cancer - but no robust evidence that earlier detection improves outcome - screening can cause harm - unnecessary treatment, can cause unwanted side effects

Question 34

Describe some evaluation difficulties

Answer 34

Lead bias - early diagnosis falsely appears to prolong survival
Only appear to survive longer because diagnosed earlier
Patients live the same length of time, but longer knowing that they have the disease

Length time bias - Screening programmes better at picking up slow growing, unthreatening cases than aggressive, fast-growing ones Diseases that are detectable through screening are more likely to have a favourable prognosis, and may indeed never have caused a problem Could lead to false conclusion that screening is beneficial in lengthening the lives of those found positive – curing people that didn’t need curing?

Selection bias - skewed by health volunteer effect
Those who have regular screening likely to also do other things that protect them from disease
An RCT would help deal with this - but difficult to carry out, especially for preexisting screening programmes

Question 35

What are some sociological critiques of screening programmes?

Answer 35

Victim blaming / Individualising pathology - a lot of responsibility on individuals to take part in screening - is everyone equally able
Individuals and populations increasingly subject to surveillance – prevention as social control?
Moral obligation - Difficult to decline screening - normative expectations about what is sensible and reasonable - if decide dont want to go for screening lots of reports as them being told they are being reckless, stupid etc. - financial incentive for encouraging people to take part in screening
Feminist critiques - Breast cancer screen and cervical cancer screens perpetuating the idea that women’s bodies are in some way less well designed/need more help???

Question 36

Why is there increasing emphasis on promoting informed choice and why is this sometimes difficult to achieve?

Answer 36

An essential attribute for any individual health professional…is to have a thorough grasp of the current state of the evidence for that particular intervention. They must clearly convey what is and what is not known, what is certain and the degree of uncertainty, so that people can make an individualised trade-off of potential benefits and harms in order to determine their own level of risk
Communicating benefits, harms and risks of preventative interventions can be challenging - lay person, public opinion, depends how much you know/up to date with research, depends how much is known by the scientific community in general