Diagnostic & Screening Tests in Respiratory Diseases Flashcards Preview

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Flashcards in Diagnostic & Screening Tests in Respiratory Diseases Deck (28)
1

What is the purpose of a diagnostic test?

To confirm the presence of disease

2

Who do you give diagnostic tests to?

Patients who already have a clinical suspicion of disease

3

What is the purpose of a screening test?

To identify patients who may have a disease or an early form of disease or a risk factor for a disease to allow for early intervention

4

Who do you give screening tests to?

Patients who have had no clinical assessment before hand

5

What is a true negative?

People who don’t have the disease and the test shows they don’t have the disease

6

What is a false negative?

People who have the disease and the test shows they don’t have the disease

7

What is a false positive?

People who don’t have the disease and the test shows the do have the disease

8

What is a true positive?

People who have the disease and the test shows they have the disease

9

What is sensitivity?

The percentage of people with the disease that test positive

10

How is sensitivity calculated?

TP/(TP+FN)

11

What is specificity?

The percentage of people without the disease that test negative

12

How is specificity calculated?

TN/(TN+FP)

13

What is the positive predictive value?

The percentage of positive tests that are actually positive

14

How is the positive predictive value calculated?

TP/(TP+FP)

15

What is the negative predictive value?

The percentage of negative tests that are actually negative

16

How is the negative predictive value calculated?

TN/(TN+FN)

17

Are sensitivity, specificity, PPV and NPV constant for a test?

Sensitvity and specificity are but PPV and NPV are not

18

What are PPV and NPV dependent on?

The prevalence of disease

19

What will the PPV be if the prevalence is low?

Low

20

What will the NPV be if the prevalence is low?

High

21

If a test has a high threshold for the definition of the disease what will the sensitivity and specificity be?

Low sensitivity but high specificity

22

What are the axes in a ROC curve?

1-specificity vs sensitivity

23

What does a linear graph on a ROC curve show?

That the test doesn’t discriminate between people with the disease who test positive and people without the disease who test positive

24

What does the area under the curve measure?

The discriminating ability of the test

25

What biases are there in screening tests?

Selection bias, lead time bias and length time bias

26

What is the selection bias in a screening test?

Healthy people are more likely to be screened because they are more motivated to undertake healthy behaviour

27

What is the lead time bias in a screening test?

A screening test might show a longer survival time than a diagnostic test - but this is only because the test is done earlier not that the test makes them live longer - the time of death could potentially be the same - early detection not prolonged survival

28

What is the length time bias in a screening test?

Diseases that have a slow enough progression to allow for a screening test have better outcomes than faster diseases - detecting of a non aggressive disease