The diagnosis of Lyme disease is based primarily on the presence of symptoms consistent with the disease and the notion of a risk of exposure, such as walks in the forest or exposure in the garden (even without memory of a tick bite). A risk of exposure and prensence of typical signs of the disease, such as an erythema migrans, are sufficient to make a diagnosis and initiate treatment.
In doubtful cases or severe cases, a laboratory test is requested. Serology (antibody testing) is the preferred laboratory diagnostic method. In case of a positive or doubtful result, a confirmatory test is performed (Western blot). Direct tests for the pathogen (microscopic examination, culture, molecular biology) can be performed in certain situations, but are only available in a few specialised laboratories and are often not very sensitive.