tspot test positive

I believe that many patients are not familiar with the professional term Tspot. It is mainly some medical knowledge, which is used to help doctors define various pathogens and cell mutations in the body, and to enable us to better judge which part of the body has abnormalities. A positive Tspot test result means that the T cells may be infected with Mycobacterium tuberculosis, which requires us to check whether the T cells are functioning normally.

1. What is the principle of T-SPOT?

T-SPOT.TB is a T cell-based in vitro IFN-γ response assay. The principle is that after the body is infected with Mycobacterium tuberculosis for the first time, sensitized T lymphocytes will be formed; when the body is infected with Mycobacterium tuberculosis again, the sensitized T lymphocytes will release higher levels of cytokines, the most important of which is gamma-interferon (IFN-γ). A high level of IIFN-γ response may indicate infection with Mycobacterium tuberculosis.

2. What is the sensitivity and specificity of T-SPOT in detecting tuberculosis patients?

According to the latest literature [1], the sensitivity and specificity of the T-SPOT method for detecting tuberculosis infection are 93.4% and 77.3%, respectively. The positive rate of T-SPOT in the tuberculosis group was 93.3%, which was higher than that in the non-tuberculosis group by 22.6%.

3. Does a positive T-SPOT result necessarily mean infection with Mycobacterium tuberculosis?

uncertain.

When the T-spot is positive, it is not necessarily confirmed to be a Mycobacterium tuberculosis (Mtb) infection. Non-tuberculous Mycobacteria (NTM), which is a general term for other mycobacteria in the Mycobacterium genus except Mycobacterium tuberculosis complex and Mycobacterium leprae, can also cause a positive T-spot reaction.

As reported in the literature, T-SPOT still cannot completely distinguish Mtb from NTM: the T-SPOT test positivity rate for Mtb patients was 96.23% (102/106); while the T-SPOT test positivity rate for NTM patients was 39.4% (28/71). The sensitivity of T-SPOT test for distinguishing Mtb from NTM infection was 96.23% (102/106), and the specificity was 60.56% (43/71).

This is because ESAT-6, antigen A, and CFP-10, antigen B, are missing in BCG and most NTM strains, with the exception of Mycobacterium kansasii, Mycobacterium marinum, and Mycobacterium sugae among NTM strains.

Therefore, in suspected cases of NTM infection, a positive T-SPOT test result does not necessarily rule out NTM infection. It is also necessary to perform pathogen testing such as NTM culture or genetic strain identification on biological samples such as sputum to provide a strong basis for diagnosis.

4. Which groups of people are suitable for using T-SPOT to screen for tuberculosis?

Please note that the T-SPOT method is not suitable for screening of tuberculosis in the general population; it is only suitable for screening of high-risk populations and auxiliary diagnosis of suspected tuberculosis:

Literature shows that the positive rates of the T-SPOT method in the general population, high-risk population and suspected population are 23.03%, 31.07% and 67.75% respectively, but the actual tuberculosis infection rates are 1.87%, 34.85% and 43.60% respectively.

T-SPOT is positive, should we intervene immediately?

When we suspect a patient with latent tuberculosis through contact history, T-SPOT and other testing methods, do we need to immediately carry out preventive anti-tuberculosis treatment (LTBI)?

The WHO's advice answers this question:

(1) Systematic testing and treatment of LTBI in HIV-infected persons, adults and children who have close contact with tuberculosis patients, patients starting anti-tumor necrosis factor (TNF) therapy, patients receiving dialysis, patients preparing for organ or blood transplantation, and patients with silicosis;

(2) Systematic testing and treatment of LTBI can be carried out conditionally for high-risk groups for TB, such as detainees, medical staff, immigrants from countries with a high TB ​​burden, homeless people, and drug users;

(3) For patients with diabetes, alcohol dependence, smokers and underweight people, if they do not fall into the above two categories, routine systematic testing for LTBI is not recommended.