Labs - Sensitivity and Specificity

 
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Sensitivity and specificity of a laboratory assay indicate how accurate the assay is for determining whether or not the person has the disease (or condition).

 

Sensitivity
Proportion of the people who truly have a disease who are identified by the assay.
This is the probability of correctly identifying a diseased individual.
Specificity
Proportion of the people who truly do not have the disease who are identified by the assay as not having the disease. This is the probability of correctly identifying a non-diseased individual. Related to sensitivity and specificity are predictive values for positive or negative tests.

 These concepts are critical to interpreting a laboratory test because high levels of false positive or false negative results have repercussions for reporting to the study participant and interpreting the factors associated with the assay result.

 

Predictive value, positive test
Assesses how many of the people who have positive test results truly have the disease.
Predictive value, negative test
Assesses how many of the people with negative test results truly are not diseased.

The expected prevalence of a disease plays an important role in determining the optimal test, i.e., the optimal combination of sensitivity and specificity. Sensitivity and specificity should be available on any assay performed, and the probabilities should be considered before committing to use an assay.

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