A doctor may diagnose Lyme disease based upon the person's clinical symptoms, such as the presence of an erythema migrans (EM) or "bull's-eye" rash, a history of a tick bite, and/or residence in or a visit to one of the areas of the country where Lyme disease is most commonly found. In cases where history and symptoms are sufficient to diagnose Lyme disease, a laboratory test is not usually ordered.
Lyme disease testing is ordered when a person has symptoms that suggest they have contracted the disease. The preferred test is a blood test to detect the presence of antibodies to the bacterium. If a person has central nervous system symptoms, such as meningitis, then testing may be performed on cerebrospinal fluid (CSF). The CDC does not recommend Lyme disease testing for people who do not have any symptoms.
- Borrelia burgdorferi IgM and/or IgG antibodies – may also be positive with infections caused by other bacteria similar to B. burgdorferi, such as the bacterium that causes syphilis
- B. burgdorferi Western Blot – ordered to confirm positive or indeterminate antibody test results
- PCR (polymerase chain reaction) testing is occasionally performed on samples such as cerebrospinal fluid or joint fluid to detect B. burgdorferi genetic material. It is a more sensitive method for detecting an infection.
- Rarely, culture of a skin biopsy may be performed to detect the bacterium.