If the ELISA is positive, an additional test called a Western blot is used to help your doctor confirm a diagnosis of Lyme disease. The UK Lyme Unit uses Western blots that test for IgM and IgG antibodies separately.
Another specific test, the polymerase chain reaction (PCR), detects the DNA of B. burgdorferi. It is used to confirm the presence of the bacterium in joint fluid in Lyme arthritis and in cerebrospinal fluid (CSF) in Lyme meningitis.
Laboratory tests are unnecessary if you have had a tick bite that becomes red and swollen when the tick is still attached or shortly after it drops off or is removed, but disappears quickly and you have no other symptoms. This is a tick hypersensitivity reaction, not Lyme disease.
If you develop the characteristic spreading rash of Lyme disease (erythema migrans) 3 to 30 days after a tick bite or possible exposure to ticks, your GP is highly likely to make a clinical diagnosis. You will be treated with antibiotics without having had any laboratory tests, and should make a complete recovery.
However, if you see your GP without a characteristic rash but with other symptoms that occur in early or later Lyme disease blood tests may be requested, particularly if you say that you have had a recent tick bite or possible exposure to ticks in wooded or long grass areas.
If the ELISA test is carried out within a few weeks of a tick bite or possible exposure it may fail to detect antibodies to B. burgdorferi, and will usually be repeated a few weeks later. About 30% of tests are positive by two weeks and about 80% by six weeks. The rate increases with duration of infection until more than 99% are positive.
If the ELISA test is positive and both the IgG and IgM Western blot tests are negative, it is probable that the ELISA result is a false positive and Lyme disease is not the cause of the symptoms.
If the ELISA and IgM tests are positive, with or without a positive IgG test, early Lyme disease is probable and treatment with antibiotics is advisable.
A positive ELISA test with a positive IgG and a negative IgM test can be seen in later Lyme disease. However, it should be born in mind that these results can also be seen when exposure to B. Burgdorferi took place a long time ago, and the current symptoms may be unrelated. This is particularly likely in people who have been exposed to tick bites at work (like foresters), during recreation (like ramblers) or because they live near woodlands or heaths.
This article was last reviewed on 5 April 2013. | This article was last modified on 11 April 2013.
The review date indicates when the article was last reviewed from beginning to end to ensure that it reflects the most current science. A review may not require any modifications to the article, so the two dates may not always agree.
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