It can be confusing when two test results disagree.
This can sometimes occur with tests used to diagnosesexually transmitted infections (STIs).
False-negative results are those in which you have a condition but the test says you don’t.
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False-positive results are those in which you don’t have a condition but the test says you do.
For example, a person’surine test for chlamydiamay be positive but theirgenital culturemay come back negative.
No diagnostic test is perfect.
While most STI tests are highly accurate if used correctly, false results can and do happen.
Sensitivity and Specificity
Most modernSTI testsare very good.
However, no test is going to be 100% accurate 100% of the time.
False-negative means that a person has an STI even though the test says they do not.
The lower the sensitivity, the higher the risk of false negatives.
False-positive means that a person does nothave an STI even though the test says they do.
The lower the specificity, the higher the risk of false positives.
One such example isHIV.
If the tests are performed too soon after infection, it may return a false-negative result.
If the test is very good at detecting the disease, it will usually find that one-in-a-million case.
How Often Should Someone Be Tested for STIs?
The answer depends largely on the throw in of STI involved.
Two such examples are chlamydia and gonorrhea, which are sometimes treated presumptively.
This means treatment is given if there’s a chance the person may be infected.
For example, sexual partners of a person who tests positive may be treated without being tested themselves.
Such is the case with HIV tests, which require a confirmatory test to accurately diagnose the virus.
When a confirmatory test is used, HIV tests are rarely ever wrong.
Summary
STI tests are very accurate, but they are not perfect.
Tests that have lower sensitivity or specificity have a higher risk of false results.
False-negative results are those in which you have an STI but the test says you don’t.
False-positive results are those in which you don’t have an infection but the test says you do.
Other factors can influence a test’s accuracy, including how common or uncommon a condition is.
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Centers for Disease Control and Prevention.HIV testing.
