screening - lecture

Question 1

what is screening

Answer 1

investigating apparently healthy people to detect an unrecognised disease/ its precursors so it can be prevented/delayed/prognosis improved
take those more likely to have condition further down the healthcare pathway
not same as diagnostic test - not perfect. people have no signs/symptoms of disease

Question 2

Results from screening test

Answer 2

false/true +ve - respect to screening test

false -ve - not benefitted from program

Question 3

challenges for screening tests

Answer 3

screen low prevalence populations
need high specificity (exclude true -ves)
lower sensitivity

Question 4

why screen

Answer 4

detection better

first do no harm

Question 5

describe screening programs

Answer 5

offered to defined population
total anomaly screening
newborn screening
diabetic retinopathy annually
vascular health checks - 40-74 year olds, check for stroke, kidney disease heart disease, type 2 diabetes or dementia
prostate cancer - risk management but no screening: benefits don’t outweigh risk
chlamydia - opportunistic

Question 6

screening can have major benefits

Answer 6

case control - see women with screening and their risk of cancer and death
reduces advanced cancer and death and risk of passing down

Question 7

Breast screening program

Answer 7

mammography
age 50-70
3 year intervals

Question 8

What is validity

Answer 8

How well the test measures what it’s meant to
whether it can identify thos with the disease and those without
split into specificity, sensitivity +ve and -ve predictive value

Question 9

how do we confirm whether a disease is present/absent

Answer 9

gold standard diagnostic test

Question 10

Sensitivity

Answer 10

ability to pick up true +ves

true +ve/all people with disease

Question 11

Specificity

Answer 11

ability to exclude true -ve

true -ve/all people don’t have disease

Question 12

Predictive value

Answer 12

proportion of test results that are correct
+ve predictive value: true +ve/true +ve + false +ve
-ve predictive value: true -ve/false -ve + true -ve

Question 13

Mammography validity

Answer 13

sensitivity 80%
soecificity 91%
PPV 4%
NPV >99%

Question 14

what is screening coverage

Answer 14

the number of people who take the test

Question 15

What epidemiological information is most important in a patient’s decision to take up screening

Answer 15

almost everyone whi has virus has cancer
prevalence of virus high
sensitivity and specificity
screening coverage - especially within her age group

Question 16

indications for screening

Answer 16

early diagnosis improves prognosis eg cancer
identifications of high risk individuals help target interventions eg lifestyle interventions for high Bp
identify those posing a risk at others - infection, TB

Question 17

Problems with breast cancer screening

Answer 17

leads to over diagnosis

more people diagnosed without screening

Question 18

Criteria for screening

Answer 18

disease - important problem, well recognised pre-clinical stage, natural history understood, long latent period
screening test - valid, simple and cheap, safe, reliable
diagnosis and treatment - facilities are adequate, effective acceptable and safe treatment available, cost effective and sustainable

Question 19

Feasibility

Answer 19

will people attend
is the test acceptable
are there the facilities

Question 20

effectiveness

Answer 20

does it improve outcomes
reduce mortality and morbidity
problem of interpretation due to: selection bias, lead time bias (survival appears to increase due to earlier detection), length bias (cases detected through screening are less aggressive)

Question 21

Cost

Answer 21

expensive
implementation, provision of diagnostic and treatment services
savings by reducing later stages

Question 22

Ethics

Answer 22

doing something to someone who is not ill
risks
false +ve = anxiety
false -ve = false reassurance

Question 23

Prostate cancer

Answer 23

high morbidity - most common male cancer
mortality - most common male cancer cause of death
tumours slow growing
first year survival 71%
more men die with than of prostate cancer
PSA - not specific to cancer, +ve predictive value 30%, -ve predictive value high
digital rectal examination - not specific, not always acceptive

Question 24

Cervical cancer screening

Answer 24

start age - if too early normal changes occur - overtreating. too late if older than 25
girls being vaccinated in school - not being ignored
if someone younger had symptoms then the screening test would be a waste of time and they would need to go to specialist treatment
increasing the age from 20 in 2003 has not increased the amount of cervical cancer
some countries vary but the International Agency for Research on Cancer concludes “There is minimal benefit and substantial harm in screening below age 25. Organized programmes should not include women aged less than 25 years in their target populations.” general trend for countries to increase the age. UK screening is a world leader because it is reviewed regularly
age range and intervals of vaccine - 25-49 every 3 years. age 50 and up every 5 years, changes are slower. only every 3 years because the virus grows slowly so wouldn’t detect anything else, if left longet 10% of cases would be missed
if not sexual active but have been you need to continue with screening
HPV-based screening provides 60–70% greater protection against invasive cervical carcinomas compared with cytology. Data of large-scale randomised trials support initiation of HPV-based screening from age 30 years and extension of screening intervals to at least 5 years.

Question 25

Vaccination for cervical cancer

Answer 25

vaccinating young people is most effective
in England already been a reduction in cancers
American academy of paediatrics support the vaccine
90% parents accept HPV vaccine for daughters
recent research says 2 doses is as effective as 3 against infection and pre-cancerous legions
currently the vaccine used is Gardasil - protects against 4 types of HPV
boys aren’t vaccinated - less at risk because not at risk of cervical cancer and vaccinating girls provides herd immunisation against the other types of cancer
from 2019/2020 school year age 12-13yr old boys will be eligible
early dose - better before they are sexually active
MSM and trans women are eligible at sexual health clinics
trans men - <45, have sex with men
Gardisol protects against 2 stains that cause 70% cervical cancer and 2 strains that protect against 90% warts