Question

Why use a home saliva test (Dr Thom etc) if it is not as accurate?

17 June 2010. Related: All topics, HIV transmission.

Thanks for the reply about the HPV vaccination and Dr Thom Saliva Test.

You say that this test is not as accurate as a blood test. If this is the case is there any point in having it done, if a negative result may not be accurate.

Answer

Answer: Simon Collins

Thanks

As noted in the earlier question one of the problems with home saliva testing is indeterminate (‘reactive’) results.

Because of the higher accuracy from a blood test, it is easier to have a blood test, which is free at any UK sexual health clinic.

Certainly anyone who thinks they may be HIV-positive would be better to have the blood test at a clinic. This is cheaper, saves the time of two tests, is accurate, and have the chance to get support in talking to someone directly after the results.

Blood tests also work after only a few weeks after the exposure risk, so instead of the stress and worry for 14 weeks before testing with a saliva test, the blood test could be done after just 3-4 weeks.

If it has been over 4 months since the risk, and the risk was low, then, according to the information on the Dr Thom website, a negative saliva test means “you’re almost certain not to have HIV”. So for someone who is at low risk and who has difficulty getting to a clinic, using a postal saliva test in may be one advantage for this type of service.

In an email from the company they provided us the following information:

Thank you for your message regarding the accuracy of our HIV saliva test.  The saliva test is not as accurate as a traditional blood test, but nevertheless the accuracy is sufficiently high to provide a good testing method.

The accuracy of all tests is segmented into what is called ensitivity‚ and specificity. A test’s ability to detect an infection when it really is there is the test’s sensitivity. A test’s ability to confirm the absence of an infection when it really isn’t there is the test’s specificity.

The sensitivity of the saliva test we use is 95 – 97%, and the specificity is quoted as 90 – 95%.  By comparison a traditional blood test has sensitivity and specificity of around 99%.