T4 TEST WILL MEASURE THE ENTIRE AMOUNT OF T4 IN THE BLOOD, INCLUDING THE AMOUNT ATTACHED TO BLOOD PROTEIN THAT HELPS TRANSPORT THE HORMONE THROUGH THE BLOODSTREAM. T4 IS PRODUCED BY THE THYROID GLAND AND HELPS CONTROL METABOLISM AND GROWTH, THIS TEST IS USUALLY DONE TO EVALUATE THE THYROID FUNCTION. T4 IS ONE OF THE MAJOR THYROID HORMONES THE OTHER ONE IS T3, THIS TEST IS USUALLY ORDER WHEN YOU SHOW SIGNS OF (HYPERTHYROIDISM, HYPOPITUITARISM, AND THYROTOXIC PERIODIC PARALYSIS "MUSCLE WEAKNESS", THYROID NODULE "LUMP IN THE THYROID GLAND").