[Patient with questionable Lyme borreliosis. Which laboratory parameters validate your clinical suspicion?].

Lyme borreliosis is the most common of the infectious diseases transmitted by ticks in the Northern hemisphere. In Europe, Lyme borreliosis can be caused by three species of Borrelia: B. burgdorferi sensu stricto, B. garinii and B. afzelii. The microbiological diagnosis is established primarily on the basis of antibody detection, and secondarily by detection of the pathogen itself. Suitable material for the detection of the latter are various body fluids (CSF, joint fluid and biopsy material, in particular in the skin). In the case of antibodies, the substrate is usually serum. If neuroborreliosis is suspected, CSF should always be investigated (CSF/serum, pairwise, same day!). The microbiological findings must be interpreted in conjunction with the clinical presentation. A negative serological result does not exclude an early manifestation, a positive finding is no proof of a clinically manifest infection--it might be a titer from an earlier infection.