Accuracy of Blood Tests for Sexually Transmitted Infections


STD/STI Tests at Clinics in London & UK »

There are many different methods and techniques by which you can test for sexually transmitted infections. These diseases, which are spread through sexual contact with someone who is already infected, will involve the transfer of microorganisms which cause the infection. Different methods of testing essentially take different approaches to detecting these microorganisms, either directly or by looking for markers that indicate their presence. Popular forms of testing include blood and urine tests, both of which are used in the UK. As with any diagnostic test, a major concern is how reliable or accurate said test can be.

Why is accuracy important in testing for STIs?

When it comes to any kind of diagnostic testing, accuracy, which is a measure of how reliable the result is, is an important consideration. A test result will obviously impact medical decisions, if a result is positive then treatment will begin, whereas if a result is negative then no treatments are pursued.

Therefore if a test is inaccurate and yields a false negative (reports the absence of an illness when it is in fact present), the wrong medical decisions can be reached, which means that conditions that can potentially cause long term damage to the body can potentially be left unchecked.

Similarly if a false positive is reported, particularly for sexually transmitted infections which can be embarrassing at the best of times, then not only is treatment wrongly provided but the patient involved will be obliged to inform former sexual partners when it is unnecessary. A false positive can be particularly devastating when life changing conditions like HIV, the AIDS causing virus, are involved.

What factors affect the accuracy of STI blood tests?

The accuracy of blood testing for sexually transmitted diseases depends on a number of different factors, the most significant of which is called ‘the window period’. This is essentially the time taken between getting infected with an STI to when a particular test can accurately detect its presence. This naturally depends on the type of testing, and is a major consideration when it comes to deciding which test to use.

The type of testing also impacts the accuracy of an STI blood test in the context of how it detects the disease causing microorganism. Some tests aim to detect the microorganisms directly, either by looking for the DNA specific to it or for the pathogen itself through a microscope. Other blood tests look for the products of your body’s immune system, referred to as antibodies, which are specific to particular bacteria and viruses and can therefore indicate their presence. The antibody blood test for example, is a reliable method of detecting Herpes Simplex provided the test is performed after the window period.

How accurate are blood tests for STIs?

When performed after the window period, blood testing for sexually transmitted infections is an extremely reliable method of detecting the presence of STIs. As a general rule, if your GP or doctor recommends a blood test, he or she will do so because they believe that a blood test is the best way of testing for a particular STI that may be responsible for your symptoms. Blood tests are only recommended and used where they are the best tool for detecting a particular pathogen.

If you are looking for a blood test privately, either through a private hospital or through an internet provider, then you should try and consult with a professional about whether or not a blood test can meet your needs. The window period and type of testing are both important considerations when it comes to making sure that you are getting the right test for you, and thereby avoiding the consequences of a false result.


« Window Period for Blood Testing for STIs Reliability of Blood Tests for Sexually Transmitted Diseases »





STD's & STI's

HEALTH CENTRES