The Absoludy TSH is a FIA (Fluorescence immunoassay) based diagnostic test for the quantitative measurement of Thyroxine, also known as T4, which is a type of thyroid hormone regulating weight, body temperature, muscle strength, and even moods. By measuring the level of FreeT4, the test can help to check if three organs (hypothalamus, pituitary and thyroid) are functioning normally.