Lyme Disease: The Test
June 1, 2012
How is it used?
Lyme disease tests are used to determine if a person with characteristic symptoms has been infected by Borrelia burgdorferi. If the doctor suspects a recent infection, then she may order both an IgM and IgG antibody blood test. If they are negative but symptoms persist, then the tests may be ordered again a few weeks later.
Acute and convalescent samples may be used to track progression of the disease by looking for changes in the amount of antibody present. If the tests are positive, then a Western blot test is ordered to confirm the findings.
Lyme disease can sometimes be challenging to diagnose. If a person has removed a tick from his skin, had a known tick bite, and lives in or has visited an area of the country where Lyme disease is most prevalent, then the timing of the potential infection can be closely estimated. However, the tick is about the size of the head of a pin and the bite may not be noticed. Not everyone will develop the characteristic rash, and the symptoms that a person does have may be nonspecific and flu-like in the early stages, with joint pain that develops into chronic arthritis and/or with neurological symptoms that appear months later.
A blood test for antibodies to the bacterium is the preferred test for the diagnosis of Lyme disease. However, if a person has central nervous system symptoms, such as meningitis, then IgM, IgG, and Western blot testing may sometimes be performed on CSF.
Occasionally PCR (polymerase chain reaction) testing is performed on a sample because it is a more sensitive way of detecting an infection with B. burgdorferi. This method is useful in detecting the infection in samples such as fluid collected from a joint. It looks for the genetic material (DNA) of B. burgdorferi in the joint fluid (synovial fluid). This method, however has not been found to be sensitive for detecting the infection in samples of CSF.
Very rarely, a sample, such as a skin biopsy, may be cultured to grow the bacterium.
Lyme disease testing is ordered when a person has symptoms suggestive of an infection with B. burgdorferi and lives in or has visited a region where deer ticks or black-legged ticks are common, especially when the person has recently been bitten by a tick.
Some symptoms of Lyme disease may include:
- a characteristic "bulls-eye" rash that spreads from the site of the bite
- fever, chills
If left untreated, Lyme disease may progress to cause:
- intermittent joint pain
- facial paralysis (Bell's palsy)
- weakness and numbness in the arms and legs
- memory problems
- may rarely affect the heart or eyes
IgM and IgG tests are ordered first. Western blot testing is ordered as a follow-up test when the first tests are positive or indeterminate. Acute and convalescent samples may be ordered several weeks apart to look for changes in antibody levels.
When someone does not have typical symptoms or a history of a tick bite and has not been in a region where Lyme disease is prevalent, then the doctor may rule out other causes for the person's symptoms before suspecting and testing for Lyme disease.
What does the test result mean?
A healthy adult who has never been exposed to the B. burgdorferi bacterium will not have any antibodies. If someone tests positive for the IgM antibody but not the IgG or Western blot test, then he may have a false positive test result or a very recent infection. If his IgM, IgG, and Western blot tests are positive, then it is likely that he has Lyme disease. If his antibody concentrations rise over time, then it is likely that he has an active B. burgdorferi infection.
If an IgM result is not detectable but the IgG and Western blot test are positive, then it is likely that the person tested either has a later stage infection or had an infection at some time in the past. If all tests are negative, then either the person's symptoms are due to another cause or the antibody levels are too low to detect.
The following table summarizes results that may be seen with Lyme disease antibody tests.
|IgM antibody||IgG antibody||Western blot|
|Positive||Positive||Positive||Likely Lyme disease|
|Negative||Positive||Positive||Late or previous infection|
|Negative||Negative||Negative||No infection present; symptoms may be due to another cause or antibody levels too low to detect|
If the result from PCR testing is positive, then it indicates infection with B. burgdorferi. If the PCR test result is negative, then there no infection is present or the levels of DNA are too low to detect.
Is there anything else I should know?
Once a person has had Lyme disease, he or she will typically have detectable amounts of B. burgdorferi IgG antibodies in their blood for the rest of their life.
Borrelia burgdorferi belongs to a class of bacteria called spirochetes. Other spirochete diseases such as syphilis and leptospirosis can cause false-positive results, as can other conditions such as HIV infection, mononucleosis, and a variety of autoimmune disorders.