Clinical Reasoning--Diagnosis (Stevens) Flashcards

1
Q

Sensitivity

A

Percent of patients with disease who are correctly identified

Sn_N_Out: want a SeNsitive test to rule Out a disease if Negative result

(Few false negatives, many false positives)

a/(a+c) = Disease positive/total disease

High sensitivity means if they have the disease they’ll be positive

Ex: D-dimer test

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2
Q

Specificity

A

Percent of patients without disease who are correctly identified

Sp_P_In: want a SPecific test with Positive result to rule disease In

(Few false positives, many false negatives)

d/(b+d) = No disease and negative/total no disease

High specificity means if they don’t have the disease they’ll be negative

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3
Q

Confidence Interval

A

Plausible range of results from the study

Use diagnosis calculator online to calculate

For 95% confidence interval that INCLUDES 0, means that if the two treatments are truly the same, a difference as large (or larger) than found in this study occurs by chance in greater than 5% of studies like this

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4
Q

Positive likelihood ratio

A

Sensitivity/(1 - Specificity)

Likelihood of + test in diseased/Likelihood of + test in undiseased

(don’t need to memorize)

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5
Q

Negative likelihood ratio

A

(1 - Sensitivity)/Specificity

Likelihood of - test in diseased/Likelihood of - test in undiseased

(don’t need to memorize)

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6
Q

Positive predictive value

A

Percent with positive test who in fact have disease

a/(a+b) = Disease positive/total positive

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7
Q

Negative predictive value

A

Percent with negative test who don’t have disease

d/(c+d) = No disease negative/total negative

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8
Q

Verification bias

A

When you decide to do the reference test ONLY if your study test is positive

You’ll miss a lot of false negatives (that are actually positive, but you’d never know)

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9
Q

When do you use a sensitive versus specific test?

A

Sensitive test first for screening, to get rid of the people you know don’t have the disease

Specific test second to confirm people who definitely do have the disease

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10
Q

Prevalence

A

People in the population who have the disease

(a+c)/(a+b+c+d)

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