The T-Spot TB is a type of Elispot blood test approved by the United States Food and Drug Administration (FDA).
A blood sample is collected from a patient with a suspected TB infection. The blood is centrifuged to separate out the peripheral blood mononuclear cells (PBMCs) which include lymphocytic T-cells. These PBMCs are washed and together with TB specific antigens, they are placed in wells pre-coated with antibodies to IFN-gamma and incubated overnight at 37 degrees C. IFN-gamma is released from the lymphocytic T-cells.
A second antibody is added which binds to the interferon antibody, now serving as an antigen A solution is then added which produces dark blue spots in the action wells where the interferon–gamma was secreted by the T–cells. These dark blue spots are counted, and depending on how many of them are present, the sample is either reported as positive, borderline/equivalent, or negative for exposure to or infection with bacteria that cause TB.
(T-SPOT. TB –P070006, United States Food and Drug Administration [FDA], CDRH Consumer Information, 2008).