Diagnosing Lyme disease




Diagnosing Lyme disease can be difficult due to the wide range of symptoms and unreliable blood tests. GPs often miss the diagnosis and there are also many uncertainties surrounding the disease, as outlined by the James Lind Alliance findings.


The EM Rash

In the early stages (between 2 and 30 days following a bite), a distinctive rash with a bull’s-eye appearance known as  erythema migrans (EM) can appear. It can vary in size and some people discover multiple rashes. This EM rash should automatically equate to a diagnosis of Lyme disease without confirmation from blood test results.  This should then lead to treatment being prescribed. The rash can often be mistaken for ringworm, cellulitis or an allergic reaction.

There is a debate over the number of people who don’t experience a rash.  A report on the year 2010 for England and Wales states that only 56% of laboratory confirmed cases displayed the rash, whereas another document detailing Public Health England’s figures from 2013 and 2014 shows that the rate of serologically confirmed cases were 19.9% and 16.4% respectively.

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. Atypical rashes are also sometimes seen in some cases and these can be varied in appearance and also difficult to recognise.

Click here for examples of the EM rash.


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 be used to rule out Lyme disease.

The initial test offered by the NHS is called an ELISA test which is usually performed at your local hospital laboratory and takes a few days or possibly a week to come back. Although there have been no specific studies to find out the percentage of false negatives in the UK, the reliability of the ELISA test appears to be questionable.

If the ELISA test is positive or equivocal, the blood sample is usually sent to the Rare and Imported Pathogens Laboratory at Porton Down in England or the NHS Highland National Lyme Borreliosis Testing Laboratory at Raigmore Hospital in Scotland. The Western blot (sometimes called an Immunoblot) is then performed. This is a slightly better test but may still miss cases.

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

Similar standard testing procedures performed in the USA appear to have a sensitivity of around 50% which means that approximately half the tests carried out could result in false negatives.

The NHS sometimes use a Cerebrospinal fluid (CSF) test for antibodies and is obtained by a lumbar puncture. An EIA is used to confirm the presence of antibodies to Borrelia. This can give a positive result before the blood serology becomes positive, but has a high rate of false negatives in Lyme disease patients.

Some patients prefer to use private specialist laboratories abroad which are favoured by private Lyme treating specialists.

Please see our testing page for more information on all types of Lyme disease testing.


Clinical Diagnoses

According to the American CDC and Public Health England, Lyme disease can be diagnosed clinically without a positive blood test result or evidence of the erythema migrans rash based on symptoms and a history of possible exposure.

However, in the UK, a clinical diagnosis is rarely made as there tends to be an over-reliance on inaccurate blood testing methods and a lack of knowledge about the disease and its symptoms. Lyme disease specialists in other countries such as the USA who are members of the International Lyme and Associated Diseases Society are more likely to give a clinical diagnosis, using testing as supplementary evidence.

The charity Caudwell Lyme Disease explores some of the issues surrounding the diagnosis of Lyme disease in the UK and the patient experience with the NHS.


N.B. We are not medical professionals