Define screening
The investigation of asymptomatic people in order to classify them as likely or unlikely to have the disease
- people will maybe have the disease you offer them further test
- screening is different → being offered a test might be surveillance
- screening is a programme
what do we need to know about screening
prerequisites for screening
need to know a few ish
- the condition should be an important (public) health problem;
- there should be an accepted treatment for the disease;
- facilities for diagnosis and treatment should be available;
- there should be a recognised presymptomatic or latent phase (i.e., early symptomatic stage)
- if the onset is sudden, can’t pick it up
- there should be a suitable test or examination;
- the test should be acceptable to the target population;
- could offer people colonoscopy put it may not be acceptable to the general public
- the natural history of the disease should be understood
- there should be an agreed policy on who to treat as patients;
- the cost should be economically balanced in relation to the cost of medical care as a whole
- usually expensive
- how good are they
- if not good may get lost of false positive
- case-funding should be continuous and not a one-off project
1. need a long term plan
2. you know do it every few years
How do we identify diseases for screening
- Disease should be relatively common and have severe consequences
a. if it doesn’t increase survival, then it may not have the severe consequence - Disease must pass through a presymptomatic phase during which it is undiagnosed but detectable
- Early treatment must offer some advantage over later treatment
- Screening should have evidence of net benefit
What is screening bias
- typically healthy people go to a screening
- women tend to go (esp healthy women)
- already have an advantage for survival
What is lead time bias
- screening period between when you detect the disease and death
- this increases because you brought the diagnosis date closer
- this increase is called lead time
- lead time bias must be accounted for when comparing survival
What is lead-time bias
- diseases that can be identified by screening are more likely to be indolent and less aggressive
- more aggressive disease is less likely to be detected because its less likely to pick up
- survival screen-detected disease may be lengthened by the less aggressive
defintion
Sensitivity
probability of a test to correctly identify disease among those with the disease
a/a+c
if you’re sensitivity is 99% then you get it right 99% of the time
Define
Specificty
proportion of people who test negative
d/b+d
how many times you get it right when people don’t have the disease
can you tell them they are deffo healthy
Define
positive predictive value
proportion with positive test who have the condition
a/a+b
Negative predictive value
proporion with negative test who dont have the condition
d/c+d
Define
false negative
They have the disease but you’re test says they are fine
define
false positives
they don’t have the diseases but you’re test says the person has the disease
how to work out prevelance
a+c/a+b+c+d
define
positive predictive value
- Positive predictive value = probability that a person with a positive test truly has the disease
- if a person tests positive, what is the probability that he/she has the condition?
Define
Negative predictive value
- ## Negative predictive value = probability that a person with a negative test does not have the disease
- If a person tests negative, what is the probability that he/she does not have the condition?
NHS breast screening programme
- The NHSBSP was established in 1988
- NHSBSP provides free breast screening every 3 years for all women in the UK aged 50 and over
- Women aged between 50 and 70 are routinely invited every 3 years; women over age 70 must request an appointment
- not done over 80 because harm of chemosurgery
problems with breast screening programme
- pick up Ductal carcinoma in-situ (DCIS) registrations have increased substantially since the introduction of NHSBSP
- , because the condition is usually not palpable and mostly diagnosed by mammography
DCIS accounts for 20& of cancers
treatment for DCIS is a wide local excision but sometimes there can be a mastectomy
What are the crituqies of the breast cancer screening programme
- for each life prolonged at least 2 women have unnecessary treatment
- 25-33% never would have been picked up and may have not caused problems
- overdiagnosis is an issue
- so for every life saved three women are overdiagnosed
even though women over 70 have a higher chance of getting breast cancer screening stopped then
why?
i acc dk
Reccomendations to increase screening uptake
- Implementing text reminders for all screening programmes
- Further pilots of social media campaigns with formal evaluation and rollout if successful
- Spreading good practice on physical and learning disabilities
- Encouraging links with faith leaders and community groups and relevant voluntary, community and social
enterprise organisations - Increasing awareness of trans and gender diverse issues amongst screening health professionals
- Consideration of financial incentives for providers to promote out of hours and weekend appointments.
potential screening tests available for prostate cancer
1) Digital Rectal Examination (DRE)
- men may be happy with this
2) Transrectal Ultrasound (TRUS)
3) Prostate Specific Antigen (PSA)
- All have disadvantages
- Of the three, the PSA test is the most acceptable and reliable, but unfortunately the PSA test has serious problems
What are the problems with PSA
- Up to two thirds of men with elevated PSA levels do not have prostate cancer
- but will suffer the anxiety, discomfort
- and risk of further investigations
- The PSA test is unreliable when undertaken in different laboratories
- The natural history of the disease is poorly understood
- and it is not currently possible to differentiate between aggressive and indolent tumours
- A substantial proportion of patients will receive unnecessary treatment, often with serious side-effects
- 15% of men with normal PSA have prostate cancer
