T3, Free, Dialysis, LC/MS-MS

A highly accurate blood test that measures free T3 (triiodothyronine), the active form of thyroid hormone that is not bound to proteins. Standard immunoassays for free T3 can be affected by interfering substances (such as biotin supplements, certain medications, or abnormal protein levels), leading to incorrect results. This test uses equilibrium dialysis to physically separate the "free" hormone from binding proteins, followed by liquid chromatography-tandem mass spectrometry (LC/MS-MS) to measure it with extreme precision. It is considered the "gold standard" for confirming complex thyroid cases, particularly when clinical symptoms do not match routine lab results. Because the procedure is labor-intensive, results typically take 6-14 days.