The most common tests used to check the health of T-cells are the T-cell Count or CD4 Count and the CD4 to CD8 Ratio T-cell test. 

T-cell Count- T-cell Count specifically measures the number of CD4 T-cells, which are crucial for coordinating the immune response. Monitoring CD4 T-cell levels is important in managing conditions like HIV, where the virus attacks these cells.

CD4/CD8 Ratio- The CD4 to CD8 Ratio T-cell test compares the number of CD4 or Helper T-cells to CD8 or Cytotoxic T-cells in your body, providing insights into the overall health of the immune system.

These tests are especially useful to monitor the immune system’s health in patients who are HIV-positive and to assess the efficacy of their treatment.