Coronavirus (COVID-19) Testing| Lab Tests Online-UK

At a Glance

Why Get Tested

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS CoV-2), which causes Coronavirus Infection Disease 2019 (COVID-19) has caused a pandemic and public health emergency due to rapid human-to-human transmission. It was first described in China in late December 2019 and the first UK case was seen a month later. It is from a family of viruses called coronaviruses. There are other coronaviruses known to cause human disease: NL63, 229E, HKU1, OC43, Severe acute respiratory syndrome (SARS), and Middle East respiratory syndrome (MERS).

There are two main types of test for COVID-19:

A swab test – this is the ‘have I got it?’ test (to test current infection).
An antibody test – this is the ‘have I had it?’ test (to test for past infection.)

Testing is very important. It gives information about how many people in the country have, or have had, COVID-19 infection. This means that it is possible to work out who needs to be treated for COVID-19, as well as to separate those with COVID-19 infection from other patients (to prevent onward infection). It can also be used to monitor the trend and spread of cases in a population, to determine what public health and societal interventions might be needed, and to assess the effectiveness of interventions, such as vaccines.

When To Get Tested

Swab tests (for current infection) are most reliable if done within the first 3 days after symptoms start. The government has now said that anyone with symptoms can be tested.It is recommended that symptomatic patients have a swab test using nucleic acid amplification (NAAT), rather than a lateral flow test (see below).

Antibody tests (for past infection) are most likely to be helpful a few weeks after the symptoms have started. Research is trying to identify the best time for testing.

Sample Required?

Swab tests for current infection are tested with a swab to the throat and/or nose. This is usually done by a healthcare professional, but home test kits are also available. This video gives further information on how to take a self-test swab.

Other samples, such as sputum, may be tested if a patient is in hospital. Saliva testing may be used in some settings.

Antibody tests need a blood sample.

Test Preparation Needed?

None

On average it takes 7 working days for the blood test results to come back from the hospital, depending on the exact tests requested. Some specialist test results may take longer, if samples have to be sent to a reference (specialist) laboratory. The X-ray & scan results may take longer. If you are registered to use the online services of your local practice, you may be able to access your results online. Your GP practice will be able to provide specific details.

If the doctor wants to see you about the result(s), you will be offered an appointment. If you are concerned about your test results, you will need to arrange an appointment with your doctor so that all relevant information including age, ethnicity, health history, signs and symptoms, laboratory and other procedures (radiology, endoscopy, etc.), can be considered.

Lab Tests Online-UK is an educational website designed to provide patients and carers with information on laboratory tests used in medical care. We are not a laboratory and are unable to comment on an individual's health and treatment.

Reference ranges are dependent on many factors, including patient age, sex, sample population, and test method, and numeric test results can have different meanings in different laboratories.

For these reasons, you will not find reference ranges for the majority of tests described on this web site. The lab report containing your test results should include the relevant reference range for your test(s). Please consult your doctor or the laboratory that performed the test(s) to obtain the reference range if you do not have the lab report.

For more information on reference ranges, please read Reference Ranges and What They Mean.

What is being tested?

The nose and throat swab are tested for the presence of viral RNA (the genetic code) which signals current infection.

Nose and throat swabs can also be used to directly detect the virus (antigen detection) by using a lateral flow test (LFT), lateral flow device (LFD), or rapid diagnostic test (RDT).

The blood is tested for antibodies which have been made because the body has been exposed to COVID-19 in the past.

Common Questions

How is the test used?

The tests are currently used to diagnose current infection (swab test) and work out past infection (antibody test).

The swab test is most useful for people who are in hospital or care homes and need to have their infection confirmed.Community testing may be useful to understand the trend and spread of cases, as well as to allow those with mild infection to isolate and therefore prevent onward transmission to others.

The antibody test is most useful for researchers who are trying to track how many people have been exposed to COVID-19, for example, in order to ensure that lockdown measures are released at the right time and plan for future healthcare.
When it is requested?

The swab test has to be performed when there are high enough levels of the virus in the nose and throat. If the person is tested too early, then there may not be enough virus present to be picked up on the test. If the person is tested too late, there may be too little virus present in the nose and throat to be found on the swab. It is done using a technique called RT-PCR which looks for genetic traces of the virus.

Antibody tests are more complicated. There are two main types of antibodies which the body makes in response to infection. IgM antibodies develop first (taking at least a week), and IgG antibodies later (about 2-4 weeks). Furthermore, some tests detect antibodies to the viral spike protein (anti-spike antibodies), while others detect anti-nucleocapsid antibodies.

There are several different ways to look for these antibodies with varying reliability. Fingerprick tests are commercially available and may be able to give a quick result (a bit like a pregnancy test), but these are of varying quality and are not recommended yet.
What does the test result mean?
Swab tests for current infection

A test showing infection (positive result) is very reliable, and means it is very likely that you have COVID-19 infection currently. NAAT is very sensitive, and patients can remain positive for some time after they have recovered. For this reason, the result needs to be interpreted alongside the clinical findings.

A test not showing infection (negative result) means you are much less likely to have COVID-19 at the time. However it is important to know that sometimes people with coronavirus can be missed by swab tests. The test could be done too early or too late to give a positive result. The technique of taking the swab might not be good enough to get sufficient virus on it to show up on the test. Lateral flow tests are less sensitive than NAAT and therefore need larger amounts of virus to be positive.

When people who have COVID-19 are missed by the test it is called a ‘false negative’. It is not known exactly how many of these false negative results are expected and this is dependent of the types of patients being tested. False negatives with lateral flow tests are far more likely than with NAAT. Patients with symptoms should be tested with NAAT.

However a false negative on either may mean a social care worker could be falsely reassured and return to work where they could pass on infection. Likewise, if a false negative result is obtained from a patient entering a healthcare setting, they may not be segregated from other patients appropriately and this risks transmission of the virus.

This is why it is very important to thoughtfully consider whether we should trust a negative test result when an ill person's symptoms suggest COVID-19 infection.

If you have strongly suggestive symptoms of COVID-19, it is safest to follow stay at home guidelines even if your swab test is negative.

Antibody tests (blood tests for past infection)

A positive antibody test means that you are likely to have been infected with COVID-19 at some time. It does not necessarily mean that you are immune.

Presence of anti-nucleocapsid antibody (with or without anti-spike antibody) is suggestive of previous infection.

Presence of anti-spike antibody (in the absence of anti-nucleocapsid antibody) is suggestive of SARS CoV-2 vaccination.

A negative antibody test means that your immune system has not produced antibodies, which means it is likely that you have not been infected with COVID-19 previously.

These tests can be done too early or too late. This means that you could think you haven’t had COVID-19, when you have. We don’t yet know how long antibodies will be able to be detected in patients who have had COVD-19 infection. There is therefore a chance that if we do an antibody test far enough in the future after a COVID-19 infection that no antibodies will be detectable. Also, a small number of patients with confirmed COVID-19 infection do not make antibodies at all. These are new tests and we expect better information about how reliable they are in the coming months.

Antibody tests are useful because it allows researchers to track how many COVID-19 infections there have been. Some people have very mild or no symptoms which means that the amount of COVID-19 in the country may be higher than the amount of people who have had symptoms from it.
Is there anything else I should know?

Many private companies are now offering testing. Before purchasing a private company test it would be useful to determine what is the benefit of knowing the result; if there is no benefit then perhaps the test is not required.

It is crucially important to know how reliable they are.

‘Accuracy’ is often given as a percentage, like ’this test is 98% accurate’.

But this doesn’t mean that 98 out of 100 tests will be correct.

This is because a test that shows an infection with COVID-19 (positive result) is more reliable when it is done in people at a high risk of disease, and it is less reliable when it is done in people with a lower risk of disease. You can read more information about this here.

It is also important to know that a test showing that you have had COVID-19 does not mean that you are immune to it.

It is a new disease and we do not have this information. Many coronavirus infections lead to some immunity, but there is not yet enough information to know whether this is useful immunity that will protect people from getting COVID-19 again.

This is why people who have had COVID-19 infection are told still to observe all the restrictions to protect against COVID-19, such as travel restrictions and social distancing.
What are the symptoms of COVID-19 infection?

For information about the symptoms of COVID-19 see NHS website.