Exams and Tests

Doctors base a diagnosis of Lyme disease on a careful and detailed history and a complete physical examination supported by laboratory testing when appropriate.

• The doctor will ask whether you know if a tick has bitten you and about outdoor exposure in an area with a high tick population.



• Physical findings are important, especially the presence of erythema migrans.



• If there is doubt whether a rash is due to Lyme disease, the doctor might measure its size and then remeasure one to two days later. Erythema migrans usually exhibits an increase in size of the rash, often expanding by about ½ inch every day.



• Some physical findings help to distinguish Lyme disease from other infectious ailments.


• Doctors may perform blood tests to examine for antibodies to the bacteria.



• Antibodies can be absent early in the course of a Lyme infection (in the first few weeks), so a negative test result may be misleading at that time.



• There are two blood tests used to diagnose Lyme disease, a screening test (Lyme ELISA) and, if that test is positive, a more specific test (Western blot). A positive Western blot test result confirms current or past infection. Especially in regions of the country where Lyme disease is very common, patients can have positive test results for Lyme disease but have clinical problems that are explained by another condition. A screening test (a Lyme titer) is not considered sufficient to make a diagnosis of Lyme disease; the Western blot has to be positive also.



• Once a Lyme blood test is positive, it will remain positive for a long time even with successful treatment. Repeat blood tests after treatment are not helpful in determining further care.



• Ixodes ticks can carry other organisms in addition to B. burgdorferi, and these can cause illnesses that can mimic Lyme disease or can even occur along with Lyme disease. The two most important infections are ehrlichiosis (HGE) and babesiosis. Doctors also may perform liver function tests and blood counts to examine the red blood cells and other tests for these two conditions.



• People with severe headaches may need a spinal tap to determine if there is inflammation in the nervous system (meningitis, encephalitis) and to test for Lyme antibodies in the spinal fluid.



• Doctors may perform an ECG if you have possible heart complications.



• CT scans and MRI of the brain may be performed to rule out other conditions that can cause similar symptoms.

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