Window Period for Blood Testing for STIs

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When it comes to accurately testing for sexually transmitted infections (STIs), the time taken since infection is an important consideration. How long it has been since you have been exposed to a particular illness affects which tests can yield the most accurate results. The amount of time between exposure to an illness causing pathogen and the point at which a test can accurately detect said illness is called the ‘window period’, and this article discusses the window period in the context of STI blood testing.

Why does the window period matter?

The window period is an important consideration in any testing because it affects how accurate the results yielded by a test are. If performed before the window period has expired, the test is not reliable and can provide a false result. An incorrectly positive result is referred to as a false positive, and an incorrectly negative result is called a false negative. If a test is administered too early, a false negative is the most likely error.

An inaccurate result can have long lasting negative consequences particularly when illnesses that can cause lasting damage are involved. Conditions like Chlamydia for example can cause lifelong damage to the reproductive system, and as the condition often does not present with any symptoms, getting the diagnosis right is extremely important.

The window period varies depending on the means of testing being used, and is an important consideration when it comes to getting an accurate diagnosis.

What is the window period for STI blood tests?

The window period for a blood test tends to vary depending on the type of test being performed. Different types of blood tests look for different markers or signs of the presence of particular pathogens (disease causing organisms like bacteria or viruses). A good example is that of the Herpes Simplex test which looks for elements produced by the immune system to combat the virus. These elements are called antibodies, and are small molecules specific to the Herpes Simplex virus which can be studied to determine whether or not the disease is present. The window period for this type of test is generally considered to be about 3 months, and this is because it takes that long for your body to generate antibodies in the quantities needed for reliable detection through a test.

Other detection methods can take less time, and the best way to determine what the window period is for a particular infection is to talk to a professional like your GP about it. A DNA amplification test for example, which aims to directly detect the presence of a pathogen, will usually have a much smaller window period than an antibody test, which has a longer window period because it takes time for an immune response to generate enough antibodies for detection.

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