EBM5: Diagnostic and Screening Tests

Question 1

Types of prevention

Answer 1

Primary: avoid developing the disease
Secondary: diagnose early and treat, like STD screening
Tertiary: Reduce morbidity and mortality

Question 2

Risk/benefits of screening?

Answer 2

Test sensitivity (how accurately can it check) specificity and predictive value has to be assessed and there has to be a cure for the disease

Also the cost of the test and the resources needed
Also do patients benefit?

Question 3

What are the preclinical phase and clinical phase

Answer 3

Preclinical starts when the disease is acquired, clinical starts when it is diagnosed, in between are the symptoms

Question 4

What are the goals of screening

Answer 4

Reduce mortality and morbidity

Question 5

What is lead time bias

Answer 5

Additional time bought when the disease is identified from screening even before the symptoms appear

Difference in the time bought by screening and the time they would otherwise had due to symptoms

Question 6

What is length bias

Answer 6

Relates to the progress of the disease whether it is slow or fast.

Disease with long bias (slowly progressing) are more likely to be detected by screening

Question 7

Which cancers are more aggressive

Answer 7

Cancers diagnosed in early screening are least aggressive, in the middle of the screening schedules are most aggressive

Question 8

What is overidiagnosis

Answer 8

Disease that can be cured but dont need to be cured since they are not the cause of death

Question 9

What is test validity

Answer 9

Tha ability of a test to determine if the person has disease and the person who doesn’t

Question 10

What is a feature of all tests

Answer 10

They all are continuous

Question 11

What is test sensitivity

Answer 11

Ability of the test to correctly identify those who have disease

False positives reduce sensitivity of a test

Question 12

What is a feature of a test with high sensitivity

Answer 12

Because of their high sensitivity we get a few false positives

Question 13

What is the concept of SNNOUT

Answer 13

We use sensitive test to rule out a disease. It is important to know why (because there is an overlap of people who dont have disease and who have disease to the right of the graph)

Question 14

What is specificity

Answer 14

The ability of a test to determine who dont have a disease

False negatives reduce the specificity of a test

Question 15

What are specificity tests used for

Answer 15

If a test specificity is high then we can correctly say that a person has a disease if their test results are positive

Question 16

How do you find sensitivity

Answer 16

TP/TP+FN, TP=Ture positives, FN = False negatives

Question 17

How do you find specificity

Answer 17

TN/TN+FP

Question 18

What is gold standard

Answer 18

A test has a perfect sensitivity and perfect specificity

Question 19

What is a positive predictive value

Answer 19

If a test result is positive then what is the probability that a person has the disease

=TP/(TP+FP)

From this you can also determine the negative predictive value

Question 20

What happens to PPV and NPV when prevalence increases

Answer 20

PPV goes up and NPV goes down slightly

Question 21

What does prevalence do for sensitivity and specificity

Answer 21

No effect

Question 22

Prevalence and predictive value

Answer 22

Prevalence can be pretest probability and predictive value can be post test proabability

Question 23

What is likelihood ratio

What does it express

Answer 23

Likelihood that the disease is present/likelihood that the disease is absent

Also + = sensitivity/(1-specificity)
And - = (1-specificity)/sensitivity

It expresses how many times more a test is likely test result is to be found in diseased people (as compared to non diseased people)

Question 24

Expands on the significance of the value of LR ratio

Answer 24

If LR is more than 10, then it is 10 times more likely that the test will come back positive for a diseased person that an healthy person

LR+ > 10, high diagnostic value
LR-

Question 25

Explain sequential testing

Answer 25

It is a 2 stage test
If the first test is negative we stop
If the 1 test is positive we do the next test
Net sensitivity is low, net specificity is high

Question 26

Explain simultaneous testing

Answer 26

These are used for screening a large number of people quickly. If the overall tests are negative, then the both tests have to be negative.
If either test is positive then either test are positive.
Net sensitivity is high, specificity is low