Diagnosis of<unk>  depends on symptoms and whether or not a<unk>  nodule is present. Most patients will receive a blood test. Others might need an ultrasound, biopsy or a radioiodine scanning and uptake study. Blood tests Overview of the<unk>  system and the various hormones involved.<unk>  function tests There are several hormones that can be measured in the blood to determine how the<unk>  gland is functioning. These include the<unk>  hormones triiodothyronine (T3) and its precursor thyroxine (T4), which are produced by the<unk>  gland.<unk> -stimulating hormone (TSH) is another important hormone that is secreted by the anterior pituitary cells in the brain. Its primary function is to increase the production of T3 and T4 by the<unk>  gland. The most useful marker of<unk>  gland function is serum<unk> -stimulating hormone (TSH) levels. TSH levels are determined by a classic negative feedback system in which high levels of T3 and T4 suppress the production of TSH, and low levels of T3 and T4 increase the production of TSH. TSH levels are thus often used by doctors as a screening test, where the first approach is to determine whether TSH is elevated, suppressed, or normal. * Elevated TSH levels can signify inadequate<unk>  hormone production (hypothyroidism) * Suppressed TSH levels can point to excessive<unk>  hormone production (hyperthyroidism) Because a single abnormal TSH level can be misleading, T3 and T4 levels must be measured in the blood to further confirm the diagnosis. When circulating in the body, T3 and T4 are bound to transport proteins. Only a small fraction of the circulating<unk>  hormones are unbound or free, and thus biologically active. T3 and T4 levels can thus be measured as free T3 and T4, or total T3 and T4, which takes into consideration the free hormones in addition to the protein-bound hormones. Free T3 and T4 measurements are important because certain drugs and illnesses can affect the concentrations of transport proteins, resulting in differing total and free<unk>  hormone levels. There are differing guidelines for T3 and T4 measurements. * Free T4 levels should be measured in the evaluation of hypothyroidism, and low free T4 establishes the diagnosis. T3 levels are generally not measured in the evaluation of hypothyroidism. * Free T4 and total T3 can be measured when hyperthyroidism is of high suspicion as it will improve the accuracy of the diagnosis. Free T4, total T3 or both are elevated and serum TSH is below normal in hyperthyroidism. If the hyperthyroidism is mild, only serum T3 may be elevated and serum TSH can be low or may not be detected in the blood. * Free T4 levels may also be tested in patients who have convincing symptoms of hyper- and hypothyroidism, despite a normal TSH. Antithyroid antibodies Autoantibodies to the<unk>  gland may be detected in various<unk>  states. There are several anti-thyroid antibodies, including anti-thyroglobulin antibodies (TgAb), anti-microsomal/anti-thyroid peroxidase antibodies (TPOAb), and TSH receptor antibodies (TSHRAb). * Elevated anti-thryoglobulin (TgAb) and anti-thyroid peroxidase antibodies (TPOAb) can be found in patients with Hashimoto's<unk> itis, the most common autoimmune type of hypothyroidism. TPOAb levels have also been found to be elevated in patients who present with subclinical hypothyroidism (where TSH is elevated, but free T4 is normal), and can help predict progression to overt hypothyroidism. The American Association<unk>  Association thus recommends measuring TPOAb levels when evaluating subclinical hypothyroidism or when trying to identify whether nodular<unk>  is due to autoimmune<unk> . * When the etiology of hyperthyroidism is not clear after initial clinical and biochemical evaluation, measurement of TSH receptor antibodies (TSHRAb) can help make the diagnosis. In Grave's<unk> , TSHRAb levels are elevated as they are responsible for activating the TSH receptor and causing increased<unk>  hormone production. Other markers * There are two markers for<unk> -derived cancers. * Thyroglobulin (TG) levels can be elevated in well-differentiated papillary or follicular adenocarcinoma. It is often used to provide information on residual, recurrent or metastatic<unk>  in patients with differentiated<unk>  cancer. However, serum TG levels can be elevated in most<unk> s. Routine measurement of serum TG for evaluation of<unk>  nodules is thus currently not recommended by the American<unk>  Association. * Elevated calcitonin levels in the blood have been shown to be associated with the rare medullary<unk>  cancer. However, the measurement of calcitonin levels as a diagnostic tool is currently controversial due to falsely high or low calcitonin levels in a variety of<unk> s other than medullary<unk>  cancer. * Very infrequently, TBG and transthyretin levels may be abnormal; these are not routinely tested. *To differentiate between different types of hypothyroidism, a specific test may be used. Thyrotropin-releasing hormone (TRH) is injected into the body through a vein. This hormone is naturally secreted by the hypothalamus and stimulates the pituitary gland. The pituitary responds by releasing<unk> -stimulating hormone (TSH). Large amounts of externally administered TRH can suppress the subsequent release of TSH. This amount of release-suppression is exaggerated in primary hypothyroidism, major depression, cocaine dependence, amphetamine dependence and chronic phencyclidine abuse. There is a failure to suppress in the manic phase of bipolar disorder. Ultrasound Many people may develop a<unk>  nodule at some point in their lives. Although many who experience this worry that it is<unk>  cancer, there are many causes of nodules that are benign and not cancerous. If a possible nodule is present, a doctor may order<unk>  function tests to determine if the<unk>  gland's activity is being affected. If more information is needed after a clinical exam and lab tests, medical ultrasonography can help determine the nature of<unk>  nodule(s). There are some notable differences in typical benign vs. cancerous<unk>  nodules that can particularly be detected by the high-frequency sound waves in an ultrasound scan. The ultrasound may also locate nodules that are too small for a doctor to feel on a physical exam, and can demonstrate whether a nodule is primarily solid, liquid (cystic), or a mixture of both. It is an imaging process that can often be done in a doctor's office, is painless, and does not expose the individual to any radiation. The main characteristics that can help distinguish a benign vs. malignant (cancerous)<unk>  nodule on ultrasound are as follows: Possible<unk>  cancer More likely benign irregular borders smooth borders hypoechoic (less echogenic than the surrounding tissue) hyperechoic incomplete "halo" spongiform appearance significant intranodular / central blood flow by power Doppler marked peripheral blood flow microcalcifications larger, broad calcifications (note: these can be seen in medullary<unk>  cancer) nodule appears more tall than wide on transverse study "comet tail" artifact as sound waves bounce off intranodular colloid documented progressive increase in size of nodule on ultrasound Although ultrasonography is a very important diagnostic tool, this method is not always able to separate benign from malignant nodules with certainty. In suspicious cases, a tissue sample is often obtained by biopsy for microscopic examination. Radioiodine scanning and uptake Five scintigrams taken from<unk> s with different syndromes: A) normal<unk> , B) Graves<unk> , diffuse increased uptake in both<unk>  lobes, C) Plummer's<unk> , D) Toxic adenoma, E)<unk> itis.<unk>  scintigraphy, in which the<unk>  is imaged with the aid of radioactive iodine (usually iodine-123, which does not harm<unk>  cells, or rarely, iodine-131), is performed in the nuclear medicine department of a hospital or clinic. Radioiodine collects in the<unk>  gland before being excreted in the urine. While in the<unk> , the radioactive emissions can be detected by a camera, producing a rough image of the shape (a radioiodine scan) and tissue activity (a radioiodine uptake) of the<unk>  gland. A normal radioiodine scan shows even uptake and activity throughout the gland. Irregular uptake can reflect an abnormally shaped or abnormally located gland, or it can indicate that a portion of the gland is overactive or underactive. For example, a nodule that is overactive ("hot") -- to the point of suppressing the activity of the rest of the gland—is usually a thyrotoxic adenoma, a surgically curable form of hyperthyroidism that is rarely malignant. In contrast, finding that a substantial section of the<unk>  is inactive ("cold") may indicate an area of non-functioning tissue, such as<unk>  cancer. The amount of radioactivity can be quantified and serves as an indicator of the metabolic activity of the gland. A normal quantitation of radioiodine uptake demonstrates that about 8-35% of the administered dose can be detected in the<unk>  24 hours later. Overactivity or underactivity of the gland, as may occur with hyperthyroidism or hypothyroidism, is usually reflected in increased or decreased radioiodine uptake. Different patterns may occur with different causes of hypo- or hyperthyroidism. Biopsy A medical biopsy refers to the obtaining of a tissue sample for examination under the microscope or other testing, usually to distinguish cancer from noncancerous conditions.<unk>  tissue may be obtained for biopsy by fine needle aspiration (FNA) or by surgery. Fine needle aspiration has the advantage of being a brief, safe, outpatient procedure that is safer and less
Thyroid disease
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Pituitary disease
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