Diagnosis is made by observation of spirochetes in a blood smear taken during a febrile episode. This is the fastest and most accessible method for most laboratories. One study reported blood smears positive 76% of the time. Peripheral blood is stained with Wright-Giemsa stain or examined with dark field microscopy.
Testing for serum antibodies is not valuable in acute settings because of the antigenic variation of the agent. Immunofluorescent assay (IFA) might be useful for convalescent patients. Culture can be accomplished on Barbour Stoner Kelly (BSK) medium and is usually positive in 24 hours. Diagnosis can also be made by inoculation of immature mice, but this is rarely performed in clinical laboratories.