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Flashcards in Session 6 - Screening Deck (25)
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Define screening

-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


Does a positive screening test mean you have the disease?

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


With reference to test validity, what is sensitivity?

-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)


With reference to test validity, what is specificity?

-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)


How do you calculate sensitivity of a screening test?

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


How do you calculate the specificity of a screening test?

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


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

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


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

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


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

-The disease
-The test
-The treatment


Outline the screening criteria for the disease aspect

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


Outline the screening criteria for the test aspect

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


Outline the screening criteria for the treatment aspect

-Effective evidence-based tx available
-Early treatment is advantageous


Which aspect of test validity does prevalence effect and how?

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


State 2 advantages of screening

-Reduces number of deaths from a certain condition
-Earlier detection of diesease prevents morbidity


What are the disadvantages of screening?

-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


Explain how screening alters the dr-pt contract

-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


Describe some limitations of screening

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


What is lead time bias?

-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


What is length time bias?

-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


What is selection bias?

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


Describe some structural sociological critiques of screening

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


Describe some surveillance sociological critiques of screening

-Individuals and populations increasingly subject to surveillance


Describe a social constructionist critique to screening

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


Describe a feminist critique of screening?

-Is screening aimed more at women than men?


Outline the aspects of the cervical screening programme

-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