There are normally between 500 and 1,000 T-cells per cubic millimeter of blood, according to AIDS.gov. T-cells send signals that activate the body's immune response when there are viruses or bacteria in the body.
A lower than normal T-cell count can signal AIDS, cancer, aging, viral infections, radiation or steroid treatment,according to MedlinePlus. A higher than normal T-cell count signals the presence of certain cancers and infections. Many factors can affect the T-cell count, such as stress, surgery, chemotherapy, immunosuppressing medications, radiation and corticosteroids. T-cell counts are measured through a simple blood test called the T-lymphocyte count or the thymus derived lymphocyte count.