Checking to see if you’ve got a sexually transmitted infection is getting easier these days. Instead of having an embarrassing wait at a GUM clinic in a remote corner of a local hospital, you can now get test kits for use at home. You can either send off your sample to a lab or get a result there and then. 

But how reliable are these test kits? And how likely is it that they will provide an inaccurate result? On this page, we’ll discuss:

What is a ‘false negative’ test result?

A false negative result suggests that you do not have a particular disease or condition when in fact, you do. Numerous medical tests can produce false negative results, ranging from pregnancy, tuberculosis and Lyme disease to tests for alcohol and drugs in the body.

For STIs like gonorrhoea and chlamydia, getting a false negative result would indicate that the person doing the test hasn’t got an infection when actually they do. This can be problematic for numerous reasons. It may mean that someone experiences delays with their treatment, due to not knowing they’re infected. It could also make it more likely that someone would inadvertently infect someone else (again, as a result of not knowing they’re infected and continuing to have sex). 

What is a ‘false positive’ test result?   

A false positive outcome indicates that you have a certain condition or disease when in actuality you do not have the disease or condition. Melanoma, a form of skin cancer, is a good example of an illness that can produce false positive results. 

In terms of tests for STIs, a false positive result for chlamydia or gonorrhoea for instance would indicate that you have the infection, when the reality is that you don’t. This can lead to unnecessary stress and anxiety for people as well as receiving treatment for no reason. In the case of gonorrhoea or chlamydia, this would involve taking antibiotics (and having an injection, for gonorrhoea), which are unnecessary, could lead to unpleasant side effects and a waste of time for patients, doctors, nurses and pharmacists. It is also a waste of health resources and money for the patient, if they’ve paid for their prescription.

What can cause a false result?

There are a number of factors that can lead to false results. You should always read the test instructions provided carefully to ensure you are conducting the procedure correctly. Laboratory errors and faulty test kits can create discrepancies, as can the absence or presence of drugs in urine. Urine samples can become compromised if you do not follow the correct protocol, for instance if take a urine sample immediately after going to the toilet (for a test to detect bacteria in the urethra, you need to ensure the first bit of urine you produce goes into the collection pot), or not posting a sample back in good time. Viral and bacterial conditions may also contribute to false outcomes, along with some medications, and pregnancy. 

How often do false positives and false negatives happen? 

The accuracy of a chlamydia test, for example, depends on the kind of test used and the type of sample that’s collected. The recommended tests are over 95% accurate in picking up chlamydia. As no test is 100% accurate, there’s a small chance that the test will give a false negative result when you do have the infection. This can sometimes explain why you might get a different result when you go to a different clinic to have another test or why you and a partner might get a different test result. It’s possible for the test to be positive if you haven’t got chlamydia, but this is rare.

Our testing partners analyse your samples according to the same process used in primary care providers and hospitals. Their processes comply with the Clinical Pathology Accreditation. You can read more about their quality assurance here.

How can I make sure my test is as accurate as possible?

You should always read and adhere to the instruction leaflet provided to carry out the test safely and correctly. It is important to check the instructions for any medications that you may already be taking that could interfere with the test result, as well as when precisely you need to send your sample back for further analysis, should it be a requirement. If you are unwell, you should also establish from reading the instruction leaflet if the virus or infection may impact on the test outcome. Take care when filling out the request form upon completion of the test, as it is essential that this information is accurate. 

What should I do if I’m not sure my test is accurate? 

If you are uncertain about your test result, you should contact your doctor or pharmacy prescriber for advice. They may recommend that you undergo a re-test, to see if it produces the same outcome.

How will I know if my result is correct?

The honest answer is that sometimes no one can know. If a result just seems incredibly unlikely (for example “I’ve had several tests and they’ve all come back negative and the only person I’ve slept with has also tested negative”) then it might be worth just repeating the test to make sure. For laboratory tests, often the lab will keep the sample and, if requested, can sometimes test it again using a different technique.

And what happens if I get a false positive or a false negative?

At, if someone’s sample is re-tested and shows the first result was inaccurate, we will refund you and offer an explanation as to what has happened. It’s not usually anyone’s fault but we understand how upsetting it can be and we offer whatever support we can for patients who experience this. Thankfully, it is incredibly rare.

Page last reviewed:  10/07/2019 | Next review due:  07/09/2021