T3 or 3,3',5-Triiodo-L-thyronine is a thyroid hormone involved with many physiological processes in the human body including growth and development, metabolism, body temperature and heart rate. Free and total T3 serum levels are measured by LC-MS/MS for determination of hyperthyroidism caused by excess T3. This Certified Spiking Solution® is suitable for use as a starting material in preparation of linearity standards, calibrators, and controls for thyroid hormone testing methods by LC-MS/MS.