T-SPOT.''TB'' is a type of

ELISpot The enzyme-linked immunosorbent spot (ELISpot) is a type of assay that focuses on quantitatively measuring the frequency of cytokine secretion for a single cell. The ELISpot Assay is also a form of immunostaining since it is classified as a tech ...

assay An assay is an investigative (analytic) procedure in laboratory medicine, mining, pharmacology, environmental biology and molecular biology for qualitatively assessing or quantitatively measuring the presence, amount, or functional activity ...

used for

tuberculosis diagnosis Tuberculosis is diagnosed by finding ''Mycobacterium tuberculosis'' bacteria in a clinical specimen taken from the patient. While other investigations may strongly suggest tuberculosis as the diagnosis, they cannot confirm it. A complete medi ...

, which belongs to the group of

interferon gamma release assay Interferon-γ release assays (IGRA) are medical tests used in the diagnosis of some infectious diseases, especially tuberculosis. Interferon-γ (IFN-γ) release assays rely on the fact that T-lymphocytes will release IFN-γ when exposed to specifi ...

s. The test is manufactured by Oxford Immunotec in the UK. It is available in most European countries, the United States as well as various other countries. It was developed by researchers at the

University of Oxford The University of Oxford is a collegiate university, collegiate research university in Oxford, England. There is evidence of teaching as early as 1096, making it the oldest university in the English-speaking world and the List of oldest un ...

in England.

Test overview

T-SPOT.''TB'' counts the number of antimycobacterial

effector T cells The T helper cells (Th cells), also known as CD4+ cells or CD4-positive cells, are a type of T cell that play an important role in the adaptive immune system. They aid the activity of other immune cells by releasing cytokines. They are considere ...

white blood cell White blood cells (scientific name leukocytes), also called immune cells or immunocytes, are cells of the immune system that are involved in protecting the body against both infectious disease and foreign entities. White blood cells are genera ...

s that produce

interferon-gamma Interferon gamma (IFNG or IFN-γ) is a dimerized soluble cytokine that is the only member of the type II class of interferons. The existence of this interferon, which early in its history was known as immune interferon, was described by E. F. ...

, in a sample of blood. This gives an overall measurement of the host immune response against mycobacteria, which can reveal the presence of infection with ''

Mycobacterium tuberculosis ''Mycobacterium tuberculosis'' (M. tb), also known as Koch's bacillus, is a species of pathogenic bacteria in the family Mycobacteriaceae and the causative agent of tuberculosis. First discovered in 1882 by Robert Koch, ''M. tuberculosis'' ha ...

'', the causative agent of

tuberculosis Tuberculosis (TB), also known colloquially as the "white death", or historically as consumption, is a contagious disease usually caused by ''Mycobacterium tuberculosis'' (MTB) bacteria. Tuberculosis generally affects the lungs, but it can al ...

(TB). Because this does not rely on production of a reliable

antibody An antibody (Ab) or immunoglobulin (Ig) is a large, Y-shaped protein belonging to the immunoglobulin superfamily which is used by the immune system to identify and neutralize antigens such as pathogenic bacteria, bacteria and viruses, includin ...

response or recoverable

pathogen In biology, a pathogen (, "suffering", "passion" and , "producer of"), in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a Germ theory of d ...

, the technique can be used to detect

latent tuberculosis Latent tuberculosis (LTB), also called latent tuberculosis infection (LTBI), is when a person is infected with ''Mycobacterium tuberculosis'', but does not have active tuberculosis (TB). Active tuberculosis can be contagious while latent tubercul ...

. This technique has the advantage that it is comparatively fast (results within 24 hours), and less influenced by previous BCG vaccination compared with the traditional testing method for latent tuberculosis, the

tuberculin skin test The Mantoux test or Mendel–Mantoux test (also known as the Mantoux screening test, tuberculin sensitivity test, Pirquet test, or PPD test for purified protein derivative) is a tool for screening for tuberculosis (TB) and for tuberculosis dia ...

. This is due to the fact that both tests use different

antigens In immunology, an antigen (Ag) is a molecule, moiety, foreign particulate matter, or an allergen, such as pollen, that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune response. An ...

for stimulation. While the tuberculin skin test uses purified protein derivative, a heterogeneous mixture of more than two hundred different mycobacterial peptides, the T-SPOT.''TB'' uses relatively ''Mycobacterium tuberculosis''-specific antigens (peptides called ESAT-6 and CFP-10). ESAT-6 and CFP-10 are expressed by ''

'', but are absent from all currently used BCG vaccines and most

nontuberculous mycobacteria Nontuberculous mycobacteria (NTM), also known as environmental mycobacteria, atypical mycobacteria and mycobacteria other than tuberculosis (MOTT), are mycobacteria which do not cause tuberculosis or leprosy/Hansen's disease. NTM can cause pulmona ...

. Based on those test principles, it is thought that the T-SPOT.''TB'' is more specific than the

Test performance

In one study in Germany, 70 out of 72 patients with confirmed TB infection were T-SPOT.''TB'' positive, indicating a sensitivity of 97.2%. However, more recent data from a study in children with active TB disease in the UK suggest that the sensitivity of the T-SPOT.''TB'' may in fact be worse than that of the tuberculin skin test (sensitivity reported as 66% and 82%, respectively). The performance of interferon-gamma release assays in children has also been questioned by other publications. A metaanalysis of studies in children with active tuberculosis published in 2011 suggests that the sensitivity of the T-SPOT.''TB'' is very similar to that of the

(pooled sensitivity reported as 84% and 80%, respectively).

References

External links

T-SPOT.''TB'' blood test for tuberculosis

Oxford Immunotec Ltd.
{{Tuberculosis Biochemistry detection reactions Tuberculosis