There are no conclusive tests for Lyme disease currently in routine use in the UK that will accurately diagnose Lyme disease or distinguish active from past infection. See our Research page for the top 10 verified uncertainties.
It is important that diagnosis is made clinically using and interpreting all test results carefully with reference to the clinical presentation. Tests are available through the NHS on blood, cerebrospinal fluid, joint fluid and tissue samples such as skin.
Anyone with a typical rash, erythema migrans, should be treated immediately without waiting for a blood test, which may be negative in early disease anyway.
Blood tests which look for antibodies to the bacteria that cause Lyme disease are the main test. This is known as serology. If antibodies have not developed sufficiently, it is possible for these tests to be negative despite active infection. Antibodies can persist for years in treated, asymptomatic patients, so positive serology does not always indicate active disease.
The NICE Clinical Knowledge Summaries  states “Testing is not generally considered to be necessary for people with erythema migrans and a history of a tick bite or possible exposure to ticks, as this presentation is sufficient to make a clinical diagnosis of Lyme disease.”
In the UK, as in the rest of Europe, the usual method of blood testing is through a 2 tier system:.
Stage 1 – An EIA or ELISA screening test is used and if this result is equivocal or positive, then the sample is sent on to a specialist reference laboratory for confirmatory testing specific to Lyme disease.
Stage 2 – the tests carried out at the reference laboratory will include an immunoblot or Western blot which is specific to Lyme disease. The aim of the second tier test is to confirm Lyme disease and identify any false positive EIA results (see following section: Is the blood test always right?)
Public Health England provides further information on Lyme disease diagnostic services for health professionals and for patients.
Is the blood test always right?
No, but we do not know how often it is wrong in the UK: there have been no studies.
False positive EIA tests (not confirmed by the confirmatory test) can be caused by cross reactions with other conditions, such as Epstein Barr virus (glandular fever), syphilis and rheumatoid arthritis and other autoimmune conditions. 
The possible reasons for a negative test in a person who genuinely has Lyme disease are:
- The test was carried out too early. Although antibodies may have developed sufficiently in the first 6 weeks, it can take longer and this is why an erythema migrans rash should be treated immediately. There is no point in delaying treatment to wait for a positive test to develop as early treatment is likely to be more effective.
- The early immune responses fluctuates, as found by a German study, so any early test is a “snapshot” which may be positive or negative. Read more in our news item.
- The person had antibiotics or immunosuppressants around the time of infection, possibly for another condition. These may reduce or even stop the antibody response so that a positive test does not develop. The most common occurrences are antibiotics given for something else (e.g. malaria prophylaxis or because of misdiagnosis of the rash as cellulitis) or when steroids have been prescribed for a facial palsy not recognised as due to Lyme disease.
- The person was infected by a strain of the bacterium that produces antibodies which are not recognised by the test. This is under-researched and it is not known how common this is.
- The person has a slow or altered immune response – as possibly in older people or pregnancy, but this is under-researched.
- Antibodies may be bound up in immune complexes which may not be detected by the EIA/ELISA test or immunoblot in the same way as freely circulating antibodies.
The screening test may not be as accurate as some authorities suggest. A paper by CW Ang et al in 2011 noted “Remarkably, some immunoblots gave positive results in samples that had been tested negative by all eight ELISAs.” 
A recent paper analysed cases diagnosed with Lyme disease in a London hospital . This reports that 11 people who had a negative screening test were thought by their doctors to have Lyme disease. Their blood was therefore sent for a Western blot despite the negative ELISA. 6 out of the 11 with a negative ELISA screening test had a positive Western blot.
Blood tests following treatment
Repeat tests may be used following treatment if the patient continues to be symptomatic or has a relapse, but the results may be inconclusive. Repeat tests may, or may not, show evidence of a rise in antibodies if there is still active disease. This may be shown on the repeat immunoblot by a new band or an increase in intensity of the bands, or in the C6 EIA by a rise in the numeric value of the test result. Although antibodies (and thus positive test results) can persist for years, there is some evidence that they decline faster in successfully treated, asymptomatic patients than in those with remaining symptoms. 
However, the immunology of Lyme disease is complex and not yet fully understood. It is not yet known whether continuing symptoms are due to active disease, tissue damage or an auto-immune response and there is no test to determine this: relapse may be a more clear cut sign of continuing disease.
Other types of test
Culture. This is the growing of bacteria in a laboratory from a sample of blood, cerebrospinal fluid or tissue. Borrelia are slow-growing, fastidious bacteria which are very difficult to culture. This technique is not usually used outside a research laboratory.
Microscopy. This is the examination of a blood smear or tissue sample using a high definition microscope to directly detect the presence of spirochaetes (the family of bacteria to which Borrelia burgdorferi belong). This is a lengthy and insensitive technique when used on blood because of the low numbers of Borrelia present except in very early infection. Insufficient trials have been done to see whether this technique may be useful in very early infection or in a relapsing period of disease, and other spirochaetal diseases would need to be excluded.
Focus floating microscopy  has been developed for detecting spirochaetes in tissue samples but this has not been used outside a research laboratory and has the practical difficulty that likely tissues must be identified and biopsied.
PCR (polymerase chain reaction). This process is used to detect the DNA of Borrelia bacteria. Because Borrelia migrate to tissues very early in infection, PCR on blood and cerebrospinal fluid (CSF) is not very successful because of the low numbers of Borrelia. PCR is more useful on tissue samples such as from skin rashes, or synovial fluid from affected joints. There has been some research into PCR on urine, but the results are inconclusive.
CSF tests for antibodies. Cerebrospinal fluid (CSF) is obtained by a lumbar puncture and an EIA used to confirm the presence of antibodies to Borrelia. This can give a positive result before the blood serology becomes positive. The Antibody Index compares paired samples of serum and CSF to determine whether there is greater intra-thecal antibody production (production of antibodies within the central nervous system itself), to help diagnose Lyme neuroborreliosis. If the infection is confined to the peripheral nervous system, CSF testing may be normal. See our leaflet on Lyme Neuroborreliosis.
Other tests on blood. Routine tests of inflammatory markers (such as CRP, ESR), CD57 tests, blood counts etc. may be normal or abnormal and are not specific to Lyme disease.
There are companies in the UK and overseas that offer private testing facilities. Before spending money on these, patients should assure themselves that accredited laboratories are used and that the tests in use are EIAs or immunoblots from a quality manufacturer and are CE marked for the diagnosis of Lyme disease. Test results from other sources are unlikely to be accepted by UK doctors.
- Clinical Knowledge Summaries http://cks.nice.org.uk/lyme-disease#!diagnosissub:3
- “Course of Antibody Response in Lyme Borreliosis Patients before and after Therapy” Aberer E, Schwantzer G.. ISRN Immunology. 2012;2012:1–4. http://www.isrn.com/journals/immunology/2012/719821/ See our discussion of this paper.
- ”Large differences between test strategies for the detection of anti-Borrelia antibodies are revealed by comparing eight ELISAs and five immunoblots. ” Ang CW et al European Journal of Clinical Microbiology and Infectious Diseases Jan 2011 http://www.ncbi.nlm.nih.gov/pubmed/21271270
- “Lyme disease in the U.K.: clinical and laboratory features and response to treatment.” Richard Dillon, Susan O’Connell, and Stephen Wright, Clinical medicine (London, England) 10, no. 5 (October 2010): 454-7, http://www.ncbi.nlm.nih.gov/pubmed/21117376
- “Disappearance of specific immune response after successful therapy of chronic Lyme borreliosis.” Hassler D, Schnauffer M, Ehrfeld H, Müller E. International journal of medical microbiology : IJMM. 2004 Apr;293 Suppl:161–4. http://www.ncbi.nlm.nih.gov/pubmed/15147000
- Focus floating microscopy: “gold standard” for cutaneous borreliosis? Eisendle K, Grabner T, Zelger B. American journal of clinical pathology. 2007 Feb;127(2):213–22. http://www.ncbi.nlm.nih.gov/pubmed/17210530
- “Diagnosis of Lyme Borreliosis.” Aguero-Rosenfeld ME, Wang G, Schwartz I, Wormser GP. Clinical Microbiology Reviews. 2005;18(3):484–509.