Thyroid Test Results
Thyroid test results are required to know if the patient is hypothyroid or hyperthyroid. After the patient is proved to be thyrotoxic, thyroid test results from the laboratory are used to establish whether hyper-function of the thyroid is due to Grave's disease or some other cause. If the patient is hypothyroid, further tests are carried out to determine the cause of hypo-function. Also, thyroid test results help the physician to establish whether the hyperthyroidism is primarily due to thyroidal disease or secondary to a pituitary disorder. A wide variety of tests are available, each measuring different facet of thyroid function and iodine metabolism. It depends upon a clinical problem represented by the patient, which test is most likely to prove helpful.
Thyroid Test Results
Serum Thyroxine: The total thyroxine level (T4) has now become the routine thyroid test, results of which determine the management of the condition. The total serum thyroxine normal range is between 5-12 micrograms per deciliter or 70-160 nanomole per liter. High T4 values are found in the thyroid test results of patients with hyperthyroidism. Sometimes, the thyroxine binding proteins may be reduced in thyrotoxicosis because of the malfunction of the lungs, a very small portion of patients have T4 values in the upper normal range. High T4 levels are also found in patients having too much thyroxine:
- In pregnancy
- in women, taking contraceptive pills with estrogens
- after treatment of hyperthyroidism with radio-iodine
- sometimes in patients with virus thyroiditis
Low T4 levels are found in hypothyroidism. In some cases of myxodema, T4 levels fall within the lower normal range. Patients suffering from Nephrotic syndrome and using cortico-steroids may also exhibit low T4 levels.
The following are the complete gamut of thyroid tests, results of which are required by the physician to diagnose a variety of disorders:
T3 Resin Uptake or Thyroid Uptake: This is not, per se, a thyroid test. It is a test on the proteins that transport the thyroid hormones around the body. A high test value may indicate a low level of the protein. The main use of the test is to compute the free thyroxine index .
Free Thyroxine Index (FTI or T7): A formula allows the computation of the free thyroxine index from the T4 and T3 Uptake tests. This thyroid test results tell the physician how much thyroid hormone is free in the blood stream to work on the body.
Free T4 Test: The free T4 test directly measures the free T4 in the blood rather than estimating it like the FTI. It is a more reliable indicator than the total T4 test.
Total T3 Test: This test is not normally ordered as a screening test by itself but is considered useful when thyroid disease is being evaluated. The Total T3 reports the total amount of T3 in the bloodstream, including T3 bound to carrier proteins plus freely circulating T3.
Free T3 Test: This test measures only the portion of thyroid hormone T3 that is "free" and not bound to carrier proteins.
Thyroid Stimulating Hormone (TSH): This hormone is secreted by the pituitary gland and regulates the thyroid gland. A high level of TSH indicates hypothyroidism while a low value suggests hyperthyroidism.
Thyroid Scan: A scintiscan or gammascan using technetium (a radioactive rare earth element) or Iodine-131 can help differentiate between Grave's disease with overall increased activity of the gland and secondary hyperthyroidism caused by a single or multiple autonomous toxic nodules.
It is important to note that no one test taken alone can give a correct diagnosis. Rather, a judicious mix of thyroid test results must be evaluated to reach a correct diagnosis.
