Diagnosing Lyme disease can be difficult due to the wide range of symptoms and a blood test that can be unreliable for various reasons. GPs often miss a Lyme disease diagnosis and there are also many uncertainties surrounding the disease, as outlined by the James Lind Alliance findings and Independent Reviews commissioned by the Department of Health.

The Erythema Migrans Rash

An infected tick bite can result in a rash known as erythema migrans (EM). This can be distinctive and resemble a bull’s-eye shape target, however it can also be atypical and some people discover multiple rashes. This EM rash is diagnostic of Lyme disease and treatment should start right away without the need for a blood test. The rash can often be mistaken for ringworm, cellulitis or an allergic reaction.

UK Health Security Agency estimate that one in every three people infected may not experience an EM rash.

Even when the rash occurs, it may be faint or on an area of the body which isn’t very visible like the scalp, behind the ears, behind the knees or on the back.

For more examples of the EM rash visit the CDC website and NICE Guideline for Lyme disease.

Blood Tests

Blood tests can be used to confirm a suspected case of Lyme disease but they are not 100% reliable and a negative result cannot rule out Lyme disease. Testing for Lyme disease is a two tier process. The first tier is an ELISA test which is usually performed at your local hospital laboratory and takes a few days or possibly a week for the result to  come back.

If the ELISA test is positive or equivocal, the same blood sample is sent to one of the national reference laboratories  for the second tier of testing, an immunoblot. These are the  Rare and Imported Pathogens Laboratory (RIPL) at Porton Down in England and the NHS Highland National Lyme Borreliosis Testing Laboratory at Raigmore Hospital in Scotland. 

You can request printouts of both of these tests and it’s advisable to do so for your own records.

Although there have been no specific studies to find out the percentage of false negatives in the UK, the two-tier testing system has its flaws.

The NHS can also use Cerebrospinal fluid (CSF) testing if neurological Lyme is suspected to be affecting the central nervous system. This incorporates testing the CSF fluid (obtained by lumbar puncture) and a paired serum (blood) sample. A definite diagnosis is confirmed by the presence of a high level of certain white blood cells (predominantly lymphocytes) in the CSF and specific antibodies to borrelia (IgM and IgG) by comparison with the blood sample plus neurological symptoms. It also requires measurement of serum albumin, IgM and IgG levels in both the CSF and the serum. 

PCR is also available and may be useful in testing joint fluid, biopsy tissue and CSF. 

Some private laboratories abroad offer Lyme disease testing but there are issues with the types of testing offered as they don’t tend to have been independently evaluated. Please note that the NICE Lyme disease guideline advises health professionals not to routinely diagnose Lyme disease based only on tests done outside the NHS, unless the laboratory used is accredited, participates in formal external quality assurance programmes and uses validated tests (see recommendation 1.2.22)

Clinical Diagnosis

According to the NICE Lyme disease guideline, the illness can be diagnosed clinically without a positive blood test result or evidence of the EM rash, based on symptoms and a history of possible exposure.

However, in the UK, doctors seem reluctant to make a clinical diagnosis and there tends to be an over-reliance on  blood testing methods and a lack of knowledge about the disease and its symptoms. The Independent Government Reviews on Lyme disease highlight uncertainties about the diagnosis of Lyme disease for patients, clinicians and researchers:

‘Patients, clinicians  and researchers report experiencing uncertainty about the diagnosis of Lyme disease. This stems from concerns that laboratory tests are not always accurate, inconsistencies in the interpretation and timing of tests, low-levels of knowledge among clinicians and challenges due to the wide range of symptoms. Patients and clinicians report that uncertainties can negatively affect clinician-patient relationships which, in turn, can lead to unproductive healthcare use and costs to society.’

‘Clinicians find it challenging to diagnose Lyme disease accurately due to the wide variation in symptoms, the infrequency with which they see the disease in practice, their level of confidence about being able to diagnose correctly, the ambiguity they experience about diagnostic tools and their beliefs and behaviour relating to atypical or recurring symptoms’ (Brunton et al, p.16)  

N.B. We are not medical professionals