Novel Approaches to TB Diagnosis  
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The Next Generation of Diagnostics

Several new developments in TB diagnostics have been developed that address many of the existing problems inherent in existing technology. All are pending approval by the FDA.

 
The Quantiferon-Gold IN TUBE Assay

The newest development in interferon-gamm release assays is the QFT In Tube Assay. The new test allows for direct application of the sample blood into a set of 3 assay tubes, one with a combination of 3 antigens (ESAT-6, CFP-10, and TB7.7) and 2 control tubes (positive control tube with phytohemaglutinin and negative control tube witha saline/heparin solution), such that no additional activation step is required. The test presents significant improvements over the original QFT-Gold test. The use of an additional antigen should allow for increased sensitivity, and the immediate application of the sample blood without intermediate stages will ensure minimal loss of live cells. The sample tubes must reach the lab within 6 hours of testing, but once ana . The test is currently in use in Europe, Australia, and Asia but is pending approval by the FDA. [Kawamura, Cellistis]

 
T SPOT-TB Test

TheT SPOT test is a form of Enzyme Linked Immunosorbent Spot (ELISPOT) assay which measures the activity of effector T cells in response to specific antigens. The T SPOT test detects the secretion of cytokines in reponse to antigens in peripheral blood mononuclear cells (PBMCs) separated from whole-blood samples. Patient blood is collected in tubes, then centrifuged to separate out PBMCs, which are then added in equal quantities to wells precoated with monoclonal antibody to a specific cytokine released in response to a specific antigen. Antigens are applied to the wells (including positive and null controls) and wells are incubated overnight. After washing, an enxyme-conjugated secondary antibody is applied to the trapped cytokines such that when treated, the enzyme complex will show colored spots. These spots will give a count of the number of T-cells that were activated in respose to the antigen employed. The T SPOT test may be less subjective in its ability to detect even individual T cells, and more sensitive than Quantiferon-type tests, tehoretically able to detect infect even in immunocompromised individuals (such as HIV +). The test is not currently approved for use by the FDA. [Oxford Immunotec Ltd]

 

A B C D

A:Null

B:Antigen A

C:Antigen B

D:Positive

 
 Image from Oxford Immunotec: http://www.oxfordimmunotec.com/products_services/howtbworks.html