Test sensitivity and specificity clarification

[MrsRonSwanson]

Can you say the opposite of SpPIN and SnNOUT are true? If a specific test is negative, it rules out disease and if a sensitive test is positive, it rules in disease? If so, then don't the results tell you the same thing?

 

 

Sorry if this has been posted elsewhere. I searched the forum and online and haven't found anything saying the opposite is true. It's been driving me nuts.

[Sara Wajek]

Sensitivity is the ability of the test to detect the presence of a characteristic in a person with that characteristic. For a test to have a high sensitivity it needs to "always" detect a characteristic when it is present. Pretend that you want to pick out everyone with brown hair out of a group of people. If you don't want to miss anyone with brown hair, you may choose some people that have light brown or dark blonde hair. Some of your dark blonde people will be "false positives," but if you didn't include them you may have excluded some people with light brown hair. For a test to be highly sensitive it will result in a higher number of false positives, but you can be sure that no one with the characteristic you are looking for is missed (false negative). (SnNOUT)

 

Specificity is just the opposite. It is the ability of the test to detect the absence of the characteristic when the characteristic isn't present. If you use the hair example again you would only choose people that you are sure have brown hair. Some of the people with light brown hair would be excluded because you couldn't be sure if they have dark blonde or light brown hair. It increases the odds of having a false negative, but you can be sure that all of your positives are correct. (SpPIN)

 

I hope that helps. I'm a lab tech, not a PA, but I would assume the definitions are the same. If PAMAC is around he'll probably have a better explanation.</SPAN>

[vegetofu]

Sensitivity rules things in & Specificity rules things out.

Here's another example: A BNP marker for congestive heart failure.

If BNP is < 100 then it is highly specific to rule out CHF (meaning you can exclude CHF if BNP <100) but BNP is not a sensitive test bc other conditions such as renal failure, age can lead to high BNP. A high BNP can help diagnose CHF but it is not a sensitive test.

Specificity is good at excluding things that are NOT PRESENT.

Sensitivity is good at including things that ARE PRESENT.

They are not the same because a test can rule things in but lacks significance in excluding things n vice versa. Hope that helps, I know it is confusing.