Screening and diagnosing tests and prognostic tools

Question 1

Define a screening test

Answer 1

simple test done an large number of asympotmatic people to detect potential disease indicators

Question 2

Define a diagnostic test

Answer 2

Generic term used to determine the nature or severity, absence or presence of a particular condition
done on symptomatic individuals (with positive screening test)

Question 3

What is the difference to the effect it has on a patient between screening and diagnostic

Answer 3

screening tests have to be accecptable to patients, no harm

diagnostic tests may be invasive and expensive, more weight given to acccuracy and precision

Question 4

What positive threshold is a screening test normally done to

Answer 4

Chosen towards a high sensitivity, so as not to miss potential disease

Question 5

What positive result threshold is a diagnostic test done to

Answer 5

High specificity - true negatives

Question 6

What does a positive result indicate in a screening test

Answer 6

Indicates suspicion of disease

in cmobination with other ris factors that warrant confrimation

Question 7

What does a positive result in a diagnostic test me

Answer 7

Definite diagnosis

Question 8

What is the cost of a screening test meant to be

Answer 8

Low because benefits could justify costs since a large number of people must be screening for few to benefit

Question 9

List the wilson and junger criteria for screening (10)

Answer 9

1- codition must be an important health problem
2- there should be an acceptable treatment that is better at an earlier stage
3-availbale diagnosis and treatment
4-recognizable latent/early sympotmatic stage
5- suitable test or examination
6- test should be acceptable to pop
7-natural history of the condition should be understoof
8-agreed upon policy on who treat as patients
9- cost of case finding should be balanced by possible expenditure on medical care
10- case finding should be a continuous process

Question 10

Define sensivity

Answer 10

The proportion of those with a disease who are correctly identified A/A+C
true positives over all positives

Question 11

Define specficty

Answer 11

The proportion of those without the disease which the test corectly identifies
D/B+D true negatives over all negatives

Question 12

Define a positive predictive value

Answer 12

The probability that the subject has the disease given that they have a positive result
A/A+B

Question 13

Define the negative predicative value

Answer 13

The probability that the subject doesnt have the disease given a negative result
D/D+C

Question 14

How can the positive predictive value be calculated

Answer 14

sensitivty x prevalence/ sensitivity x prevalence + (1-specificity) x (1-prevalence)

Question 15

What are the benefits of screening

Answer 15

may produce and earlier diagnosis
earlier diagnosis may improve prognosis
Disease may be prevented
Save money if treating early is cheaper

Question 16

What are the disadvantages of screening

Answer 16

Cost money
Worried well
cause harm directly
no screening test will identify all disease
screen negative patient may delay prsenting sympotoms is disease is falsely reassured
there will be false positives
there will be over diagnosis

Question 17

Explain lead time bias

Answer 17

lead time is the time between diagnosis of a disease with a test and the time it would have otherwise presented, might appear to prolong life without there being any real benefit

Question 18

Explain length time bias

Answer 18

The tendency of a screening test to select cases with a sow progression. in the intervals between tests a rapid progressing disease may kill people.