EBM5: Diagnostic and Screening Tests Flashcards Preview

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Flashcards in EBM5: Diagnostic and Screening Tests Deck (26)

Types of prevention

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


Risk/benefits of screening?

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?


What are the preclinical phase and clinical phase

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


What are the goals of screening

Reduce mortality and morbidity


What is lead time bias

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


What is length bias

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


Which cancers are more aggressive

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


What is overidiagnosis

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


What is test validity

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


What is a feature of all tests

They all are continuous


What is test sensitivity

Ability of the test to correctly identify those who have disease

False positives reduce sensitivity of a test


What is a feature of a test with high sensitivity

Because of their high sensitivity we get a few false positives


What is the concept of SNNOUT

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)


What is specificity

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

False negatives reduce the specificity of a test


What are specificity tests used for

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


How do you find sensitivity

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


How do you find specificity



What is gold standard

A test has a perfect sensitivity and perfect specificity


What is a positive predictive value

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


From this you can also determine the negative predictive value


What happens to PPV and NPV when prevalence increases

PPV goes up and NPV goes down slightly


What does prevalence do for sensitivity and specificity

No effect


Prevalence and predictive value

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


What is likelihood ratio

What does it express

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)


Expands on the significance of the value of LR ratio

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


Explain sequential testing

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


Explain simultaneous testing

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