The T-SPOT.TB test involves a series of steps starting with a blood sample and resulting in a determination of TB infection. Here's a breakdown of the process:
Steps in a T-SPOT.TB Test
The T-SPOT.TB test is a blood test used to detect tuberculosis (TB) infection. It focuses on identifying specific immune cells that respond to TB bacteria.
Blood Collection and Preparation
- Blood Draw: A standard blood sample is taken from the patient using a routine blood draw method called phlebotomy.
- PBMC Isolation:
- From the collected blood, a specific type of white blood cell, known as peripheral blood mononuclear cells (PBMC), are isolated using lab techniques.
- These PBMCs contain the key immune cells, like T-cells, that are relevant for detecting TB infection.
- Cell Washing: The isolated PBMCs are washed to remove any unwanted components.
- Cell Counting: The cells are counted to ensure there are enough cells for the next steps.
- Standardization: Finally, the cell suspension is normalized to ensure that the concentration of cells is consistent.
The T-SPOT.TB Procedure
- Cell Incubation:
- The standardized PBMC suspension is added to wells in a special plate.
- Some wells contain specific TB antigens (proteins that stimulate an immune response).
- Other wells will contain a control substance.
- Incubation Period: The plate is then incubated for a set time period to allow the cells to react to the antigens if TB infection is present.
- Counting Spots:
- After incubation, the cells undergo a process to detect the presence of interferon-gamma (IFN-γ), a protein released by stimulated T-cells when exposed to TB antigens.
- The number of spots (corresponding to IFN-γ-producing cells) in each well are counted.
- Result Interpretation:
- If there is no infection, there will be no significant IFN-γ spots.
- If there is TB infection, the T-cells will produce IFN-γ when exposed to TB antigens, resulting in more spots being seen.
- The results are interpreted based on the number of spots observed in the test wells compared to the control well.
Key Elements and Comparison
| Element | Description |
|---|---|
| Blood Sample | A standard blood draw is the first step. |
| PBMCs | Peripheral blood mononuclear cells are isolated. |
| TB Antigens | Specific proteins of TB bacteria are used to stimulate T-cells. |
| IFN-γ | A marker of T-cell response to TB. |
| Spots | Visible indications of IFN-γ production, counted to determine results. |
This test is designed to be a more specific and sensitive test for TB infection compared to the Mantoux test. The test does not rely on the patient’s general immune reaction, but focuses specifically on their T-cells reacting to TB proteins.
