The Bartonella IgXSpot test is an Enzyme–Linked ImmunoSpot (ELISPOT) assay that detects human T cells reactive to Bartonella specific antigens in vitro, including B. henselae, B. quintana, B. elizabethae, and B. vinsonii. It detects specific T cell responses soon after Bartonella infection or late in the disease. This test is unavailable for patients over 65 when ordered through physician services.