STI Testing & False Negative Results

One of the most important considerations in the realm of diagnostic testing is the accuracy and reliability of the testing procedure itself. Accurate results are an important part of diagnostic medicine as they form the basis of the most important clinical decision: whether you suffer from a particular illness or not. In this article we look at one of the big concerns when it comes to diagnostic testing, particularly in the field of testing for sexually transmitted infections.

What is a false negative result?

In the realm of testing for infections, including sexually transmitted diseases (STDs or STIs), erroneous results can be split into two categories: false positives and false negatives. False positives are results which incorrectly report the presence of an infection, while false negatives are the opposite, wrongly reporting the absence of an infection.

What causes a false negative result?

In the design and development of STD tests there are two important considerations, specificity and sensitivity. The latter is the test’s ability to detect an illness, while the former is a test’s ability to specifically detect a particular infection. If a test is overly sensitive then the chances of a false positive are increased as it may inaccurately report the presence of an infection, whereas if a test is overly specific it may result in a false negative.

STI tests are designed to balance sensitivity and specificity, and thereby reduce the chances of an inaccurate diagnosis.

False negatives can also occur because of the timing of a test. If a test is performed within what is called the window period of a particular infection then the chances of a false negative are elevated. The window period varies between tests and infections, and is essentially the time taken between the point of infection and when a particular test can detect a specific infection accurately. Testing within the window period affects the reliability of results, and this can be, for example, because of an insufficient amount of antibody if an antibody test is being used.  

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