About the saliva test

Hampshire and Isle of Wight Saliva Testing Programme follows a successful pilot in Southampton, where students and staff in four local schools and the University of Southampton were tested on a weekly basis.

Read more about the success of the pilot programme.

How does the saliva test work?

The saliva test is very simple – all participants need to do is provide a small 2ml sample of saliva in a pot and return it to a drop-off point.

This is then transported to a laboratory, where it is tested for genetic material of the virus in saliva samples using a technique known as loop-mediated isothermal amplification (LAMP).

The result of the saliva test will tell participants whether or not they have an active COVID-19 infection at the actual time they took the test. This test does not tell participants whether they had the virus in the past, and a negative result does not protect them from catching it in the future.

As with all tests, people can test negative if they are in the early incubation phase of developing an infection, so may test positive at a later time.

What’s the difference between the saliva sample testing and swab testing?

The saliva test uses saliva provided in a small pot by participants. This is very simple and easy to do at home. The swab test requires a swab to be taken from the back of the throat and high up in the nose either by the participant or a healthcare professional.

The saliva test used in our programme and the swab test check samples for COVID-19 using different techniques.

Saliva samples are tested for the virus using a technique known as loop-mediated isothermal amplification (LAMP).

In the UK, swab samples are currently tested for the virus using different techniques called polymerase chain reaction (PCR) testing or lateral flow testing.

The LAMP technique can be conducted reliably, and more quickly than the PCR test, which is currently the standard reference test. In validation studies across multiple laboratories in the UK and in other countries, positive samples from LAMP tests have been ‘double tested’ against PCR tests and shown to be highly accurate.

What’s the difference between the saliva sample testing and lateral flow tests?

Lateral flow tests are used with swab samples and identify presence of the virus. The tests work in a similar way to a pregnancy test, giving a positive line if the virus is detected in the sample. One benefit of these tests is that results can be read in 10-30 minutes, but current evidence is that these tests have more ‘false positives’ and ‘false negatives’ than LAMP tests.

Is a saliva sample as good as a swab sample in picking up the active virus?

Yes. The pilot testing programme showed that all kinds of RT-Lamp tests, on saliva and swab samples, have a 99% specificity, making them almost completely accurate at picking up COVID-19.

Is the saliva LAMP test accurate?

Saliva test samples analysed using the loop-mediated isothermal amplification (LAMP) technique have been ‘double tested’ against tests using the polymerase chain reaction (PCR) testing method.

LAMP has been shown to be highly accurate in detecting active infections– 100 per cent specific (the ability to correctly identify those without the virus) and over 95 per cent sensitive (the ability to correctly identify those with the virus). This means that false positives are extremely rare and false negatives can occur but are not common.

Could you get a different result from a saliva LAMP test and a swab PCR test on the same day?

Given the variety of COVID-19 tests available, it can be challenging to identify the appropriate test for use in a given scenario. Please note that tests must not be used interchangeably for symptomatic and asymptomatic testing. The levels of sensitivity for the various sample sites (saliva, throat/nose swab) differ, with PCR regarded as the gold standard. LFD and saliva LAMP tests are therefore currently recommended for use as screening tests in people without symptoms.

At our state of the art laboratory, saliva testing detects the most infectious asymptomatic individuals. However, a single test only detects the viral load at the particular time the sample was provided, in the area of the body it was taken from, and is also dependent on the sample being provided correctly. As the amount of circulating virus changes, there may be different results between tests, even within short timeframes. These factors limit our ability to directly compare available tests, which all serve a purpose in breaking chains of transmission. The important message is to test regularly to reduce the spread as much as possible.

Can you get a different result from any other test?

No test is perfect. There is a possibility that a lateral flow test and saliva LAMP test result may give different results. This could be due to the manner in which the lateral flow test is conducted by the individual. The saliva LAMP test is a very reliable test which picks up more true positives and has fewer false positives than lateral flow tests.

What is a false negative?

A false negative result is when the test is reported as negative when the person really has an infectious virus present, which has not been picked up. The published pilot programme report shows that this is not common with the saliva LAMP test.

What if I test negative on the saliva test and a few days later test positive?

A negative saliva LAMP test tells you that at the time of sample collection there was no detectable infectious virus particle in the saliva. However, if the test is taken during the incubation period in the early days after a person has been infected, the number of virus particles may not yet be at a detectable level, and so a person could go on to test positive on a subsequent day.

To date, evidence from both our pilot programme report, the original validation data and our updated preprint data is that the rate of false negative saliva LAMP tests is low for active infections and very similar to that of the reference swab PCR tests.

It is also possible to test negative one day and positive soon after if a new infection is acquired after the negative test. Find out more about what to do if you test positive.

What is a false positive?

A false positive is where the test result is positive but there is no infectious virus present. We have tested many thousands of samples within this Programme and have had no false positive results - so you can be confident, if you test positive and you/your household need to isolate, it is because you have the virus.

Will my saliva sample be used for anything else?

Your saliva sample will only be tested for COVID-19. No DNA will be extracted or stored. If your test result is positive, your sample may be sent off for further genotyping (a process of detecting the differences within a person’s genes, by examining their DNA), in order to contribute to research about variants.

Can I use a saliva test if I have symptoms?

If you develop COVID-19 symptoms, you should not take a saliva test. You should self-isolate pending a PCR test.

The aim of the programme is to offer weekly saliva testing to participants who are not showing symptoms of the virus but could be infectious. Testing methods must not be used interchangeably for symptomatic and asymptomatic cases. The levels of sensitivity for the various sample sites (saliva, throat/nose swab) differ, with PCR regarded as the gold standard. LFD and saliva LAMP tests are therefore currently recommended for use as screening tests in people without symptoms.

Information:

If you have symptoms, you should order a test via the NHS national testing programme that has been set up for this purpose. The national testing programme will offer you either a postal test kit, or an appointment at a site for testing.

Why is asymptomatic testing important?

Testing people without symptoms of COVID-19 is important as it can identify those who may be spreading the virus but aren’t aware of it. Many people with COVID-19 don’t have symptoms but can still transmit the virus, and those who do develop symptoms can be infectious for a few days beforehand.

Once someone knows that they have the virus, they, their household and close contacts must follow government advice around self-isolation, reducing the chance of it being spread to their family and friends, as well as anyone else they may come into contact with.

Asymptomatic testing within schools, colleges and universities can help us to continue to offer education in COVID-secure environments.

Should I continue taking regular tests if I am isolating?

If you are isolating due to a positive test result or because you are a contact of someone who has tested positive, you should not continue testing. Please complete your full isolation period. A negative test would not shorten your isolation period. Once you are no longer isolating, continue testing regularly as you did before.

If you are based in a school and have been asked to take regular tests instead of self-isolating as a contact, please follow the instructions you have been given.

If you are based at university and have been asked to isolate until you have had two negative tests, then please follow the instructions provided by the university.

How does virus infection work?

Viruses are a kind of microorganism, which can be transmitted between people to cause infections.

Once a virus infection has been detected in the body, the immune system works to fight it off, often causing symptoms like fevers, headaches and rashes. However, there may be some cases where people do not experience any symptoms at all. This is know as being asymptomatic.

The average time between the exposure to COVID-19 and symptoms developing is estimated as five days, and for most people, it is four-six days. For some people, this time may be as short as two days or as long as 14 days.

The introduction of vaccines that combat virus infections involves inserting non-infectious fragments of the virus into your body, to produce the antibodies and other tools it needs for combating the virus. People may experience generally minor symptoms such as fevers, while the body is building up its immunity against the virus.

Once an infection goes away due to the body producing a sufficient number of antibodies and white blood cells to fight it, it will leave a ‘memory’ in the body. These are essentially cells that will allow us to remember how to fight the virus if we experience it again in the future.

When should I resume saliva LAMP testing after a positive test result?

For Saliva LAMP testing you should start testing again once your period of self-isolation following the positive test has ended. The rules for self-isolation following a positive test are as follows:

  • If you have symptoms – self-isolate for 10 days from when your symptoms started.
  • If you have not had symptoms – self-isolate for 10 days from when you had the test.
  • If you get symptoms while you're self-isolating - the 10 days restarts from when your symptoms started.

Guidelines for resuming testing for alternative COVID-19 tests will differ due to varying technical aspects, alongside test specificity and sensitivity levels. The PCR test can give a persisting positive result beyond the period when a person is infectious, because it can detect fragments of virus that are not infectious. This may result in positive results even when an individual is no longer infectious.

By contrast, technical aspects and the high specificity of saliva LAMP testing means that if a saliva test is positive, there is a very strong likelihood that the participant can transmit the virus to others. This is the case irrespective of whether they have recently experienced a COVID-19 infection or had a positive PCR result.

LFD Testing should not be used for 90 days following a positive PCR test. However, you can continue to use saliva tests.

Should I continue with the testing programme if I've had the vaccination?

Yes, please keep testing as planned. No vaccine is completely effective and so it is still possible for you to get infected and pass the virus on to others.

Will the fact that I've had a vaccination affect my test result?

No, the vaccine will not affect your test result. The vaccine itself won't cause you to test positive. The test picks up infections, not your response to the vaccine.

What are the benefits of saliva testing compared with lateral flow testing?

Both RT-LAMP saliva and lateral flow device (LFD) tests are currently recommended for asymptomatic screening. This means that both tests are suitable for use in cases where an individual is not showing any symptoms of COVID-19, but could be transmitting the virus to others.

As COVID-19 infects salivary glands first, saliva testing is an effective test for identifying the most infectious individuals prior to symptoms. It is a non-invasive, accessible testing option, especially for those for whom nasal or throat swabs are more difficult to tolerate.

Studies have shown that saliva samples processed using LAMP technology provide highly reliable results, especially for those infected with and/or shedding high levels of virus. False positives are extremely rare; while false negatives can occur, they are not common.

Confirmatory tests are routinely undertaken at our state of the art laboratory, so if a saliva sample is positive, it is only rarely necessary to organise an additional COVID-19 PCR test through the NHS. Positive saliva samples are also additionally tested to identify the particular strain or variant of the virus to help with disease monitoring.

All COVID-19 tests have specific uses and serve a purpose in breaking chains of transmission. The important message is to test regularly to reduce the spread as much as possible.

Please note:

  • A single test only detects the viral load at the particular time the sample was provided, in the area of the body it was taken from;
  • The reliability of test results is also dependent on the sample being provided correctly, as per the instructions for use;
  • Saliva testing is an asymptomatic screening test;
  • Tests must not be used interchangeably for symptomatic and asymptomatic people because the levels of sensitivity for the various sample sites (salivary glands/ throat/ nose) differ.
  • If you develop COVID-19 symptoms, follow the latest guidelines; a PCR test is currently regarded as the gold standard test for use in symptomatic cases.
How does the positivity rate for saliva testing compare to other testing methods?

Positivity rate refers to the percentage of all COVID-19 tests that are resulted as positive. Our positivity rates are consistent with other national asymptomatic saliva testing centres.

It is not possible to directly compare the positivity rates of different COVID-19 tests for the following reasons::

  • Saliva LAMP testing is currently recommended for asymptomatic screening, whereas PCR tests are performed in symptomatic patients.
  • LFDs are often misused for symptomatic testing (60-70% of total use), while misuse of saliva testing is less common.
  • PCR testing data picks up genomic remnants, so the positivity rates reflect what is known as ‘period prevalence’. This means that PCR tests may detect viral fragments of COVID-19 virus from a previous infection. A PCR test may produce a positive result after you are no longer actively infectious for a period of up to 90 days.
  • By comparison, saliva testing is designed to identify those shedding the highest viral load at the time of providing a sample, so the positivity rates reflect what is known as point prevalence. This means that saliva testing is unlikely to detect viral fragments from a previous infection.