Thyroid Assays

Thyroglobulin (Tg) is a glycoprotein found in thyroid follicular cells that plays a critical role in the biosynthesis of key thyroid hormones. The measurement of anti-Tg antibody has been shown to be an aid in the diagnosis of Hashimoto’s thyroiditis and Graves’ disease. The Siemens Healthineers anti-Tg antibody assays provide a precise, quantitative determination of anti-Tg antibody in serum or plasma.

Anti-thyroid peroxidase antibody (anti-TPO antibody), a protein found in thyroid follicular cells, is a catalyst in the synthesis of key thyroid hormones. Autoimmune thyroid diseases are characterized by the presence of anti-TPO antibody.

Elevated levels of anti-TPO antibody are a risk factor for:

• Autoimmune thyroid disease, including Hashimoto’s thyroiditis, Graves' disease, atrophic thyroiditis and primary myxedema
• Postpartum thyroiditis in women

The Siemens Healthineers Anti-TPO Antibody assay is a competitive immunoassay that uses chemiluminescent technology. It is a highly sensitive test for the detection of anti-TPO Ab2, giving laboratorians an accurate, quantitative determination of anti-TPO antibody in serum or plasma.

Triiodothyronine (T3) is a hormone synthesized and secreted from the thyroid gland, and formed by peripheral deiodination of T4. T3 plays an important role in regulating metabolism.

• In the circulation, 99.7% of T3 is reversibly bound to transport proteins. Unbound T3 (free T3) is metabolically active.
• The Free T3 test helps determine whether the thyroid is functioning properly. It is ordered primarily to help diagnose hyperthyroidism and may be ordered to help monitor the progress of a patient with a known thyroid disorder.
• The Free T3 test is usually ordered following an abnormal TSH and T4 test. Free T3 testing may be ordered along with thyroid antibodies to help diagnose Graves’ disease, an autoimmune disorder that is the most common cause of hyperthyroidism.

Thyroxine (T4) is a hormone synthesized and secreted by the thyroid gland and plays an important role in regulating metabolism. In the circulation, 99.95% of T4 is reversibly bound to transport proteins. The remaining T4 is not bound to transport proteins, but is free in the circulation. This unbound fraction, free T4, is metabolically active. An appropriate FT4 assay used in combination with TSH is considered by the American Thyroid Association to be "the best and most efficient combination of blood tests for the diagnosis and follow-up of most patients with thyroid disorders.”¹

The most important characteristic of a thyroglobulin assay is how reliably the assay discriminates between the assay’s functional sensitivity and the lower limit of the normal reference range, signaling residual thyroid tissue after thyroid ablation.

Thyroglobulin aids in monitoring patients who have undergone thyroidectomy. They help to evaluate treatment and patient outcomes, including thyroid cancer recurrence and metastasis and radioactive iodine ablation, when the thyroglobulin level usually becomes very low or undetectable. If the level is low and then starts to rise, it is concerning for possible cancer recurrence. The presence of thyroglobulin antibodies (TgAb) should also be measured to improve interpretation.

Siemens Healthineers offers an automated and reliable thyroglobulin test that exceeds the high-performance characteristics necessary for identifying the presence or absence of functioning thyroid tissue.

TBG binds thyroid hormones in circulation. It is one of three proteins responsible for carrying T3 and T4 into the bloodstream. TBG tests are sometimes used in finding the reason for elevated or diminished levels of thyroid hormone.

For quantitative measurement of total triiodothyronine (T3) hormone in human serum and plasma. Measurements of T3 are used in the diagnosis and treatment of thyroid diseases such as hyperthyroidism and T3-thyrotoxicosis.

Total T4 is a hormone used to help diagnose hyper- and hypothyroidism. The Total T4 test is usually ordered with a TSH test to help determine whether the thyroid hormone feedback system is functioning properly, and the results help to distinguish between causes of hyper- and hypothyroidism.

TSH stimulates the thyroid gland to synthesize and secrete thyroid hormone. TSH serum measurements are used to detect primary hypo- and hyperthyroidism and are also important for thyroid cancer patients. Most thyroid cancer patients who have had a thyroidectomy require thyroid hormone replacement with levothyroxine after the thyroid is removed. The TSH level is a good indicator of whether the levothyroxine dose is correct.

The capability of a TSH assay to distinguish between normal and subnormal concentrations is essential for thyroid testing strategy. Quantification of TSH at a lower value of 0.01 mlU/L yields information that is useful to clinicians referring patients with subnormal TSH concentrations. Siemens Healthineers TSH assays consistently deliver sensitive, highly specific results across multiple platforms.

TSH, 3rd Generation
Improvements in the sensitivity of TSH assays allow them to be used for detecting both hyper- and hypothyroidism. Assays with a functional sensitivity of <0.02 mIU/L are classified as third-generation assays. The 3rd Generation TSH assay from Siemens Healthineers is sensitive and precise, with imprecision performance that exceeds the criteria recommended by the NACB for TSH methods.

TSI measurements are also used to monitor the response to Graves' disease therapy and predict remission or relapse, confirm Graves' ophthalmopathy, and predict neonatal thyroid hyperthyroidism.^2,3

The IMMULITE^® 2000/2000 XPi TSI assay is the first automated, quantitative TSI assay available. TSH receptor antibody (TRAb) assays detect both thyroid-blocking and -stimulating antibodies. However, blocking antibodies inhibit TSH stimulation of thyroid cells and lead to hypothyroidism. The IMMULITE 2000/2000 XPi TSI assay detects thyroid stimulating antibodies, the specific cause of GD pathology, with a clinical sensitivity and specificity of 98.3% and 99.7% respectively. With a 65-minute total assay time and ready-to-use, stable reagents, the use of this assay can make the differential diagnosis of GD faster and easier, allowing patients to be diagnosed and treated sooner.