Your doctor will ask about your symptoms and perform a complete physical and neurological examination. If you have had a recent tick bite and have saved the tick, your doctor may want to inspect the insect and send it to a laboratory to identify the species. Some laboratories can analyze the tick to see if it's carrying Lyme bacteria.
Your doctor will diagnose Lyme disease based on your symptoms and the examination. Blood tests are often negative in the first four to six weeks of Lyme disease. The basic Lyme test is called an ELISA (enzyme-linked immunosorbent assay). However, this test often gives a false-positive result, that is, a positive result in someone who doesn't have the illness. Therefore, every positive or uncertain Lyme ELISA result needs to be confirmed with a test called a Western blot, which looks for more specific evidence of Lyme disease infection.
A positive Lyme blood test, even including a Western blot, doesn't mean that the disease is active and needs to be treated. This is because blood tests can remain positive for years, even after Lyme disease has been treated or has become inactive. To help diagnose Lyme disease and to check for other causes of symptoms, a sample of fluid may be withdrawn from an affected joint using a sterile needle. Cerebrospinal fluid also may be taken from around the spinal cord through a spinal tap (lumbar puncture), to test for Lyme disease antibodies and inflammation and check for other diseases.