06. Diagnostic Testing Flashcards Preview

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Flashcards in 06. Diagnostic Testing Deck (18):
1

Sensitivity

"True positive rate"; Proportion of people with disease who have a true positive test result; How good a test is at detecting people with disease; Insensitive to prevalence

2

Specificity

"True negative rate"; Reflects how good the test is at IDing people without disease; unlikely to produce false positives; insensitive to prevalence

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True positive

Test positive & disease present

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False positive

Test positive & disease absent

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True negative

Test negative & disease absent

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False negative

Test negative & disease present

7

Likelihood ratio (LR) definition

The likelihood that a given test result would be expected in a patient with the disease compared to the likelihood that the same result would be expected in a patient without the disease. Can be a positive or negative value.

8

Importance of likelihood ratio

Useful for assessing the value of performing a diagnostic test. Use the sensitivity & specificity of the test to determine whether the test result will significantly change the probability that a disease exists.

9

LR+ Equation

[Sensitivity/ (1-specificity)]; Amount by which the pretest probability is INCREASED in pts with POSITIVE test

10

LR+ Interpretation

SUPPORTS TRUE DISEASE; Should be slightly significant above 1. LR+ >10 causes large shift in posttest probability of disease

11

LR- Equation

[(1-sensitivity)/specificity]; amount by which the pretest probability of disease is REDUCED in patients with a NEGATIVE test

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LR- Interpretation

Supports NO DISEASE; Should be significant

13

LR = 1

No shift in probability of disease

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Predictive value importance

Sensitive to prevalence; indicates what the test MEANS to the patient

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Positive predictive value

% of positives that are TRUE POSITIVES; [True positives/All positives]

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Negative predictive value

% of negatives that are TRUE NEGATIVES; [True negatives/All negatives]

17

Parallel testing

Shotgun; Many tests at once. ANY positive is diagnostic. INCREASES SENSITIVITY. Reduces risk from lack of intervention.

18

Series testing

Rifle; Sequence of diagnostic tests - ALL tests must be positive for diagnosis (think about tests needed to confirm +HIV status); INCREASES SPECIFICITY; Reduces risk of unnecessary intervention. Reduces sensitivity.