Flashcards in HaDSoc 6.1 Screening Deck (30)
What are the different forms of detection of a disease?
-spontaneous presentation (the patient presents to GP/A&E etc because of symptoms)
-opportunistic finding- a patient will present to healthcare with one thing, then the professional will test for other things whilst they are there, and may find other problems eg hypertension.
-screening- asymptomatic pateint gets screened to see if they probably do/dont have a disease.
describe features of screening:
-done on asymptomatic patients
-tells you whether you probably do/dont have a disease.
Process of identifying healthy people who may be at increased risk of a disease.
Information, further tests and treatment is offered to reduce associated risks/complications.
What is the main purpose of screening?
To improve the prognosis of the disease if it gets picked up. To give a better outcome
(Not just to detect it earlier)
Give examples of population screening programs.
-diabetic eye screening
-newborn blood spot.
What are the 5 criteria which help you decide if screening is appropriate?
What features about the condition need to be considered when thinking about screening?
-is it prevelant (wont screen for something that only a few people have)
-is it severe enough to warrant screening
-have all the cost effective primary interventions been implimented beforehand?
What features of the test need to be considered when thinking about screening?
-is it simple, safe, valid?
-is it acceptable to the public?
-have cut of levels been established?
-have the further investigations been established.
Why does a screening program need to be simple and safe?
You'll be conducting it on healthy individuals, it's unfair to put them through extensive screening when there is nothing to be found.
What are the 2 mistakes that can be made in screening?
-false positive (the patient has tested positive but do not have the disease)
-false negative (The patient has tested negative but actually does have the disease)
What issues surround a false positive result?
a healthy individual will be turned into a patient and will undergo tests/examinations etc which they do not need.
A lot of unnecessary anxiety will be experienced.
oppertunistic costs (spending money on people who do not need it, when there are people who do need it who now cant use that money).
May be less likely to take up screening in the future
What issues surround a false negative?
-you're giving someone false reassurance
-may mean they present later than they would have which could lead to a worse prognosis down the line.
What features of a screening test test it's validity?
-positive predictive value (PPV)
-Negative predictive value (NPV)
What is meant by sensitivity (Screening)?
How many people who have the disease test positive?
Also known as the detection rate.
true positives+false negatives.
What is meant by specificity? (screening)
What is the probability that someone without the disease will test negatively?
true negatives + false positives.
What is special about sensitivity and specificity? (Screening)
They are consistent.
The same test applied in the same way will get the same sensitivity and specificity.
Do you want sensitivity and specificity to be high or low?
What is a positive predictive value?
If i have tested positive, what is the chances of me actually having the disease?
true positive + false positive
What is a negative predictive value?
if i have tested negative, what are the chances of me not having the disease?
true negative + false negative.
What is the positive predictive value strongly affected by?
The prevalence of the disease.
(will be lower in lower prevalence populations, may test positive but the chances of you having the disease are slim)
Do you want positive predictive values to be high or low?
from the view of the patient, you'd want it to be low, (if you've tested positive you want it to be unlikely that you actually have the disease)
From the view of screening, you want it to be high. You dont want to incorrectly test positive for people who dont have the disease, you want a lot of the people coming up positive to actually have it.
What features do you want from an intervention if you're considering screening?
-intervention must be known to increase outcomes.
-HCW should know what interventions take place when there is a positive result.
What features about the screening programe need to be considered when thinking about screening?
-needs to have proven effectiveness at reducing mortality/morbidity.
-needs to be acceptible
-benefits to patients should outweight harms
-oppertunity costs must be balanced with medical expenditure.
What factors surrounding implementation need to be considered when thinking about screening?
-there should be adequate staffing/facilities.
-there should be a monitoring program
-all other options for managing the condition should have been considered
What are the main problems associated with screening?
-lead time bias
-length time bias
-public pressure to have other screening programs
What is lead time bias?
Becuase of earlier detection, it looks as though people live longer, when in fact they just know about the disease for longer.
Make survival look better, when it isnt.
What is length time bias?
Screening favours slow growing conditions rather than fast growing/aggressive conditions.
Detected conditions are more likely to have a favourable outcome anyway, may not have needed treatment.
What is selection bias, with regards to screening?
the people who go to screening programs are more likely to do other things that promote good health too, such as eating well, adherance.
Why do people need to be given an informed choice about screening?
-need to know about the risks of testing incorrectly, and what that could mean.