Protein-bound iodine (PBI) is a laboratory test that measures the amount of iodine bound to proteins in the bloodstream, primarily to the thyroid hormone thyroxine (T4). T4 is a hormone produced by the thyroid gland that helps regulate metabolism and other physiological processes in the body.
In the PBI test, a small amount of radioactive iodine is administered to the patient, and the amount of iodine bound to proteins in a blood sample is measured. The test is typically used to assess thyroid function, as changes in PBI levels can indicate problems with thyroid hormone production.
An elevated PBI level may indicate hyperthyroidism, a condition in which the thyroid gland produces too much thyroid hormone. Conversely, a decreased PBI level may indicate hypothyroidism, a condition in which the thyroid gland produces too little thyroid hormone.
While the PBI test can provide useful information about thyroid function, it has largely been replaced by newer, more accurate tests such as the thyroxine (T4) and thyroid-stimulating hormone (TSH) tests. These tests are more sensitive and specific than the PBI test, and are able to detect changes in thyroid function at earlier stages of disease.
