Lyme disease testing

DISCLAIMER: Caudwell LymeCo charity shares public domain  information, which it believes to be reliable, in good faith. It should never replace the advice of a qualified physician with a licence to practise medicine. If you believe any information on this website to be incorrect, you are invited to contact the charity using the Contact page.

The procedure for Lyme disease testing outlined below is used by the NHS in the UK.

NHS Lyme disease testing

Before the test

To order an NHS blood test for Lyme disease, your GP first needs to be convinced you have a reasonable risk of having been bitten by a tick and/or that you have Lyme disease symptoms.

Bear in mind that:

  1. Lyme disease symptoms take from 3 days to 3 months to develop after a bite.
  2. It usually takes several weeks for Lyme disease antibodies to form, and if the test is done before they have formed, it will be negative. If a test is performed too early and is negative, but the patient has symptoms, the test should be repeated.
  3. For many people, the tick is long gone by the time they notice any Lyme disease symptoms.
  4. Some people believe that there are “hotspots” or “Lyme endemic areas” in the UK and may think the risk of Lyme disease is extremely low outside these areas. In reality, there are no data to tell us which regions of the UK may have more ticks than others, or what percentage of the ticks in any area may carry Lyme disease.
  5. It is sometimes claimed that ticks are only found in forests and overgrown countryside, but in fact they are also present in urban parks and gardens.

Local testing (ELISA test)

Different types of a type of test called an ELISA test are used in different testing laboratories around the country.

If you live in an area where demand for Lyme disease tests is high, there may be a local laboratory which your blood may be sent to for initial testing using an ELISA test (see below).

If this test is positive your blood will be sent to a national reference laboratory for a repeat ELISA test and a western blot test. (For a description of these tests, see the FAQ section below.)

National Reference Laboratories (the two-step test)

If you live in an area where Lyme disease tests are rarely requested, your blood is more likely to be sent directly to one of the two national reference laboratories.

  • The Rare and Imported Pathogens Laboratory (RIPL) in Salisbury, England tests samples from patients in England, Wales and Northern Ireland, whilst
  • the National Lyme Borreliosis Testing Laboratory (NLBTL) at Raigmore Hospital tests samples from Scotland.

The national reference laboratories do a “two-step” test, first an ELISA test and then a western blot (or immunoblot) test. The NICE guideline for Lyme disease advises repeating one or both steps of this test under certain circumstances.

You can ask your doctor for printouts of your test results.

Some frequently asked questions

The following is a summary of the current policies and regulations surrounding NHS Lyme disease testing in the UK, based on public domain information. THIS SHOULD NOT BE INTERPRETED AS AN EXPRESSION OF THE CHARITY’S OPINION ON ANY ISSUE REGARDING DIAGNOSTIC TESTING. This does not constitute diagnostic advice, and the charity does not provide interpretations or advice based on any diagnostic test results. You should always take the advice of a medical doctor with a licence to practise medicine.

What does laboratory accreditation mean?

Most countries have a national authority which inspects medical laboratories, and issues an accreditation number and certificate if they comply with all the standards in a written protocol. The standards cover hygienic handling of samples to avoid contamination, building standards to ensure air hygiene, accurate keeping of patient and sample records to ensure the each person receives the right test result, and many other details necessary for a reliable and safe laboratory.

The accreditation authority in Britain is called UKAS and the old British protocol was the CPA standard. Another, similar protocol called ISO 15189 has been adopted in more and more countries and is now regarded as the international standard. Laboratories in the UK are switching to this protocol.

What does a CE marked test mean?

The CE mark issued by the European Union is not used to certify tests for diagnosing patients, but is used to mark test kits produced for laboratory research experiments. It certifies, amongst other things, that the kit does contain the antigens, and have the other features, stated in its description/labelling. It does not certify the test kit’s reliability or any of its performance criteria.

What does a validated test mean?

If a test is validated, this means that it has been evaluated by researchers independent of the manufacturers, and the results of their research have been published in a scientific paper. The test would be evaluated for its sensitivity and specificity (see below) using a large number of samples of blood, or other body tissue, urine etcetera as relevant.

Much of the research which has so far been carried out on Lyme disease diagnostic tests is disappointingly low in quality. (The term low quality generally refers to risk of bias, and imprecise reporting of results.) Several private laboratories offer tests which are still regarded by the medical community as being in the research phase, because they have not yet been researched as described above.

Some diagnostic tests for Lyme disease may show great promise, and others may not. We will not know until more research is done. Raising money to fund research into different types of Lyme disease test is one of Caudwell LymeCo Charity’s key objecties. How you can help>>

What does the ‘sensitivity’ of a diagnostic test mean?

The sensitivity measures how well the test can find out if a person has the condition being tested for. It is expressed as a percentage or as a decimal fraction of one. A sensitivity of 0.9 or 90% would be more reliable than a sensitivity of 0.6 or 60%. If a test has a sensitivity of 90%, it means 90% of people who have the relevant disease will get a positive result using that test.

A test with low sensitivity runs the risk of ‘missing’ some patients, meaning they may not receive treatment for a disease they have.

What does the ‘specificity’ of a diagnostic test mean?

The specificity measures how well a test can find out if a person does NOT have the disease being tested for. So a test with a specificity of 0.8 or 80% is much more reliable than a test with a specificity of 0.3 or 30%. If a test has 80% specificity, it means that 80% of people who get a positive result in that test really do have the disease being tested for, but the remaining 20% of the people who get a positive result do not really have the disease.

A test with low specificity runs the risk of giving people a false diagnosis for a disease they do not really have, meaning they might receive unnecessary treatment, and that they might not be tested or treated for a different disease that they really have.

What does accredited test mean?

When laboratories are accredited, each of the diagnostic tests they provide are also checked. If the tests are validated satisfactorily, they will be listed as accredited. If they are not validated in accordance with the required standard, they will be excluded from the accreditation. The accredited laboratory can continue to offer the test to its customers but the test will not be an accredited one.

What is an external validation scheme?

The aim of diagnostic tests is to produce the same result on every sample, every time, no matter which laboratory performs the test. Some laboratories collaborate to check if this is really the case, by performing the same tests on the same samples of blood and comparing results.

The Rare and Imported Pathogen Laboratory (part of Public Health England) participates in a scheme of this kind with laboratories across Europe to validate the Lyme disease testing it provides to NHS doctors in England and Wales.

What is the Lyme disease ELISA test?

ELISA stands for enzyme-linked immunosorbent assay. This test is performed on a plate with rows of small recesses, so lots of samples can be tested at once. ELISA tests can be used for detecting and quantifying substances such as peptides, proteins, antibodies and hormones, so ELISA tests are used to diagnose a great many different conditions. The Lyme disease ELISA test looks for antibodies to Borrelia burgdorferi. Other names, such as enzyme immunoassay (EIA), are also used to describe the same technology.

Versions of the Lyme disease ELISA test are manufactured by various companies and the NHS/National Reference Laboratories use several of them. A large number of research papers report varying sensitivities for this test, based on evaluating different companies’ products. In general, they report a higher sensitivity than specificity, because all versions of the test can give a false positive result for people who have some other conditions rather than Lyme disease.

Some types of Lyme disease ELISA tests use “native antigens”, which means a mix, produced from actual Borrelia burgdorferi bacteria, of the parts of the outer surface which human antibodies recognise and attach to. There are various strains of Borrelia burgdorferi and not all of the antigens from all of them can be included in the ELISA test. They would number in the thousands, and many of them would be identical to the proteins from many other types of bacteria or other, harmless organisms. Borrelia burgdorferi also has an outer surface which mutates repeatedly. This means it is possible for a person to have Lyme disease, and to have antibodies to it, but not to have antibodies to the particular antigens included in a “native antigens” ELISA test kit. this would mean they would get a false negative test result.

For this reason another type of ELISA test was developed, using a protein called C6. This is the only protein which is found in all strains of Borrelia burgdorferi, and which does not mutate. The test aims to have a higher sensitivity than the “native antigens” test.

What is the Lyme disease western blot test?

The western blot (sometimes called the protein immunoblot) is used to detect specific proteins in a sample of blood (or sometimes other types of sample). For a Lyme disease western blot, a blood sample is mixed with antigens of the Borrelia burgdorferi bacteria which causes Lyme disease. If there are antibodies in the person’s blood sample which fit these borrelia antigens, they will attach to them and can be detected by a machine which reads the test strip.

Why does the NHS require two tests for Lyme disease?

Neither the Lyme disease ELISA nor the Lyme disease western blot is a perfect test. The ELISA test for Lyme disease sometimes gives false positive results, as it can react to pathogens other than Borrelia burgdorferi, and it also sometimes gives false negative results. The Western blot has a higher specificity than the ELISA test, which means it is better at finding out which of the people with a positive ELISA test result may not really have Lyme disease. This system of performing both tests is called two-tier testing, and its aim is to achieve a more accurate result than using one test alone.

Even the combined test is by no means perfect and for this reason, it is also very important for the doctor to take into account the person’s symptoms.

Is it possible to have seronegative Lyme disease?

In all infectious diseases, it is known that some people never produce antibodies even though they are infected. For the diseases in which this has been researched, it is believed to happen very rarely. It is not known how commonly this may happen for Lyme disease.

Why won’t my NHS doctor prescribe me treatment based on my positive private Lyme disease test?

NHS doctors rely on validated, accredited tests performed by accredited laboratories which particiate in an external validation scheme. The only tests for Lyme disease which are currently validated are the ELISA and the Western blot, and UK doctors know that NHS approved laboratories fulfil all the required criteria.

Patients who have received a positive Lyme disease test result from a non-NHS laboratory can be re-tested on the NHS, and can be treated on the NHS if the result is positive. In England and Wales the laboratory for two-tier testing will the Rare and Imported Pathogens Laboratory and in Scotland it will be Raigmore Hospital. These are the two national reference laboratories in the UK.

Do NHS doctors accept test results other than ELISA or western blot for Lyme disease?

In general no, because other Lyme disease tests have not been researched or validated, and therefore are not accredited. There are some other types of test, which may be used by NHS doctors in addition to the two-tier tests, in specific circumstances. Some of these tests analyse body tissues other than blood. It is our understanding that the NHS only relies on these other tests if they are carried out in NHS approved testing laboratories.

Do NHS doctors accept ELISA or western blot test results from private laboratories overseas or in the UK?

Whilst some private laboratories are accredited and may offer accredited ELISA or western blot tests, we do not know of any private laboratories which participate in an external validation scheme similar to the one in which the UK national reference laboratories participate. For this reason, it is our understanding that currently tests from other laboratories are not accepted by NHS doctors.

There is a laboratory in the USA called IgeneX which offers its own interpretation of a western blot test for Lyme disease. Although their test is a western blot, their way of defining which result is positive and which is negative has not been independently evaluated for sensitivity or specificity. For this reason, NHS doctors to not treat patients on the basis of this test.

Are all ELISA tests for Lyme disease ordered in England and Wales carried out by RIPL?

In some areas where Lyme disease testing is more frequently ordered, there are NHS hospitals which can offer the Lyme disease ELISA test. If this is positive, the person’s blood is forwarded to RIPL where a new ELISA is performed, and also a western blot. In areas where Lyme disease is less often suspected, there may be no regional hospital so doctors may send a sample directly to RIPL.

If I got a negative Lyme test less than 6 weeks after a tick bite, might I really have Lyme disease?

Antibodies to Borrelia burgdorferi take up to 6 weeks to develop, and during the first six weeks after being infected, a Lyme disease test could be negative. If the first test was negative within this time frame but there are still symptoms, the test should be repeated.

If I got a negative test more than 6 weeks after being infected, might I really have Lyme disease? 

It is possible.

There are different suspected explanations of why some symptomatic  patients may test negative for Lyme disease using two-tier blood testing.

  • The tests can sometimes be wrong.
  • Ticks carry a number of infections and some of them have similar symptoms to Lyme disease. An illness following  tick bite may be a different infection, not Lyme disease. More information >>>
  • The two-tier testing process used by the NHS looks for antibodies to the bacteria, not the bacteria itself. Some researchers think that Lyme disease suppresses the immune system so much that the antibody levels may be too low in some patients to detect using these tests.
  • Antibodies may not have formed yet. Some research has suggested that the antibody response to Lyme disease can be unpredictable and may take longer than 6 weeks to develop in some people, and also that the level of antibodies may fluctuate over periods of months. Find out more>>

Is it true that the national reference laboratory (Rare and Imported Pathogens Laboratory) at Porton Down is not nationally accredited?

This is not true. The national reference laboratory is CPA accredited.

Why won’t the staff at RIPL (Rare and Imported Pathogens Laboratory) discuss my Lyme test results with me?

Put simply, RIPL can discuss your results with your doctor, but it is against regulations for them to discuss results with patients. Doctors who consult with patients are registered by the General Medical Council in the UK. It is a criminal offence for a doctor to practise medicine in the UK – which includes giving any advice to patients –  if he/she is not registered with the GMC.
Link to GMC register: Medical Register

Scientists who work in medical laboratories in the UK are required to hold a different type of authorisation to perform their tasks within the laboratory.

Testing in private laboratories

Some people decide to pay for Lyme disease testing at private laboratories. If you decide to spend money on private testing, be prepared to pay for private treatment as well.

NHS doctors only treat patients who have been diagnosed by NHS-approved laboratories. Some private doctors who specialise in treating patients for Lyme disease also advise patients to have a test at a specific laboratory and may not treat based on tests from other laboratories.

More information provides additional information on Lyme disease diagnostic tests.