Key thyroid tests help your doctor make a diagnosis whether your thyroid is functioning properly, after assessing your symptoms and examining your thyroid. These thyroid tests may include any or some of the following:
Complete Blood Count. A complete blood count (CBC) plus metabolic profile are important thyroid tests, helping to determine that there is no anaemia, liver malfunction, excess blood calcium and other possible causes.
Thyroid stimulating hormone (TSH). Thyroid test for TSH levels give the best indication of thyroid function. If you have hypothyroidism, the level TSH increases, while it is undetectable or low in patients with hyperthyroidism. TSH normally should range between 0.4 to 5.5 micro international units per millilitre of blood (micro IU/ml). Patients with hyperthyroidism usually have below 0.1, while those with hypothyroidism have elevated levels above 5. Young healthy patients have TSH below 3.0.
Total and free thyroxine (T4). These two thyroid tests are measured separately from each other. Total T4 testing measures all thyroxine circulating in blood; free T4 testing measures only the biologically active thyroxine (those not bound to serum-binding proteins and can attach to the hormone receptors in cells). This thyroid test references a normal range for free T4 among (non-pregnant) women at 0.8 to 2.7 nanograms per decilitre of blood (ng/dl), while the normal range for total T4 is 4.5 to 12.5 micrograms per decilitre (mcg/dl). If you have Graves’ disease, your total T4 would be more than 12 mcg/dl; those with hypothyroid have total T4 below 5 mcg/dl.
Total triiodothyronine (T3). This thyroid test measures the T3 levels circulating in the blood. The normal reference range is 0.4 to 4.2 micro IU/ml. This blood test is usually conducted when your doctor needs more information about the function of your thyroid.
Thyroid antibody blood tests. These thyroid tests detect antibodies to thyroid cell components, such as antibodies to thyroglobulin and thyroperoxidase. High levels of these various antibodies can help confirm Graves’ disease.
Radioactive iodine uptake (RAIU). RAIU may usually be required when there is a presence of a goiter or thyroid nodules. This thyroid test may also be done together with a thyroid scan. You will be given a small amount of oral radioactive iodine to measure the total amount absorbed by your thyroid gland. Absorption rate is normally 8-30 percent after twenty-four hours. In Graves’ disease, radioactive iodine will show levels above 30 percent. It will also be elevated in postpartum thyroiditis and in women having replacement thyroid hormone.
Thyroid scan. A thyroid test scan measures the amount of radioactive iodine absorbed by the thyroid and the evenness of its dispersion. If the entire thyroid absorbs the radioactive iodine, it eliminates the possibility that overactive nodules are inducing hyperthyroidism. A benign nodule producing too much thyroid hormone will appear “hot” on the scan, compared with a “cold,” under-producing nodule, which is either benign or malignant.
Ultrasound. This thyroid test may be done if your doctor feels nodules when examining your thyroid. Ultrasound pictures of thyroid nodules felt during examination help determine whether they are solid or filled with fluid, including nodules that cannot be felt.
Needle aspiration biopsy. A biopsy may be taken from suspicious nodules. In this thyroid test, a needle withdraws some fluid or cells for analysis. Detecting cancers up to 90 percent accuracy is possible with this thyroid test.
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