Session 6 - Screening

Question 1

Define screening

Answer 1

-Systematic attempt to detect an unrecognised condition which can be done rapidly to distinguish those who are likely to have disease from those who haven’t

Question 2

Does a positive screening test mean you have the disease?

Answer 2

-No, it means you are high risk and diagnostic tests must be performed.

Question 3

With reference to test validity, what is sensitivity?

Answer 3

-Proportion of people with the disease who test positive (how good the test is at getting a positive result from those who have the disease)

Question 4

With reference to test validity, what is specificity?

Answer 4

-The proportion of people who do not have the disease which test negative (how good the test is at getting a negative result if you do not have disease)

Question 5

How do you calculate sensitivity of a screening test?

Answer 5

-Disease present +ve/ (disease present +ve and -ve)

Question 6

How do you calculate the specificity of a screening test?

Answer 6

-Disease free -ve /(disease free +ve and -ve)

Question 7

What is the positive predicted value? How do you work this out?

Answer 7

• How likely a person is to have the disease when they have tested positive
• Disease +ve /(disease +ve + disease free +ve)

Question 8

What is the negative predicted value? How do you work this out?

Answer 8

• How likely a person is to be disease free when they have tested negative
• disease free -ve/(disease free -ve + diseased -ve)

Question 9

What 3 groups of criteria are there when referring to screening criteria?

Answer 9

• The disease
• The test
• The treatment

Question 10

Outline the screening criteria for the disease aspect

Answer 10

• Must be an important health problem
• Epidemiology and natural history must be well understood
• Must have an early detectable stage

Question 11

Outline the screening criteria for the test aspect

Answer 11

• Simple and safe
• Precise and valid with an agreed cut off
• Acceptable to population being screened
• Agreed policy on who to investigate further

Question 12

Outline the screening criteria for the treatment aspect

Answer 12

• Effective evidence-based tx available

- Early treatment is advantageous

Question 13

Which aspect of test validity does prevalence effect and how?

Answer 13

• PPV

- The higher the prevalence the higher and more accurate the PPV

Question 14

State 2 advantages of screening

Answer 14

• Reduces number of deaths from a certain condition

- Earlier detection of diesease prevents morbidity

Question 15

What are the disadvantages of screening?

Answer 15

• Many people have to be screeded to sace 1 life -> costly, invasive and causes unneccesary worry and anxiety
• Some people detected by screening die anyway
• People diagnosed with disease without harm or symptoms may be subjected to reduced QoL due to checkups
• Refers well people for investigation -> false positives
• Fails to refer people who have the disease -> false negatives -> ess likely to present if symptoms occur as been told low risk
• Overdiagnosis of diseases which wouldnt have caused harm

Question 16

Explain how screening alters the dr-pt contract

Answer 16

• Normally patients self present asking for help
• Screening targets apparently health people who have not sought help and offers help for something they havent thought about

Question 17

Describe some limitations of screening

Answer 17

• Cannot guarantee protection
• Always false +ves and -ves
• Need for informed choice on whether to have screening or not
• Always unneccessary investigations

Question 18

What is lead time bias?

Answer 18

• Early diagnosis falsely appears to prolong survival as screened patients appear to survive longer but were only diagnosed earlier
• Patients live the same length of time but a longer period knowing they have the disease

Question 19

What is length time bias?

Answer 19

• Screening programmes are better at detecting slow growing, unthreatening cases vs fast agressive cases
• Therefore diseases detected by screening are already more likely to have a favourable prognosis

Question 20

What is selection bias?

Answer 20

-Skewed by ‘healthy volunteer’ effect. Those who attend screening are more likely to be doing other things to protect themselves from disease

Question 21

Describe some structural sociological critiques of screening

Answer 21

• Victim blaming -> individuals encouraged to take responsibility for own health - can everyone do this?
• Individualising pathology -> What about addressing underlying material causes of disease

Question 22

Describe some surveillance sociological critiques of screening

Answer 22

-Individuals and populations increasingly subject to surveillance

Question 23

Describe a social constructionist critique to screening

Answer 23

-Health and illness practices can be seen as moral - given meaning through particular social relationships

Question 24

Describe a feminist critique of screening?

Answer 24

-Is screening aimed more at women than men?

Question 25

Outline the aspects of the cervical screening programme

Answer 25

• Aims to decrease the number of invasive cervical cancers and deaths
• Women aged 25-64 years -> 25-49 3 yearly: 50-64-> 5 yearly; 65+ only those who had recent abnormalities
• under 25s not screened due to lots of false negatives as invasive cervical cancers rare under 25
• normal results -> continue screening
• Abnormal result -> analysed -> either no tx or laser ablation LLETZ
• Incorporates HPV test -> +ve referred to colposcopy