Sorted By Test Name - Mayo Medical Laboratories

HTG1
83069
This cutoff has been validated for total needle wash volumes of < or =1.5 mL of normal saline. If wash
volumes are substantially larger, a lower cutoff might apply.
Clinical References: 1. Pacini F, Fugazzola L, Lippi F, et al: Detection of thyroglobulin in fine
needle aspirates of nonthyroidal neck masses: a clue to the diagnosis of metastatic differentiated thyroid
cancer. J Clin Endocrinol Metab 1992;74(6):1401–1404 2. Frasoldati A, Toschi E, Zini M, et al: Role
of thyroglobulin measurement in fine-needle aspiration biopsies of cervical lymph nodes in patients with
differentiated thyroid cancer. Thyroid 1999;9(2):105–111 3. Snozek CL, Chambers EP, Reading CC, et
al: Serum thyroglobulin, high-resolution ultrasound, and lymph node thyroglobulin in diagnosis of
differentiated thyroid carcinoma nodal metastases. J Clin Endocrinol Metab 2007;92(11):4278-4281
Thyroglobulin, Tumor Marker, Serum
Clinical Information: Thyroglobulin (Tg) is a glycoprotein (660,000 MW) composed of 2,748 amino
acids, which contains 8% to 10% carbohydrate and iodine. The amount of iodine varies with the dietary
intake of the individual. Seventy percent of the Tg monomer is composed of repeat sequences. Tg is
present in the serum of normal individuals. It is secreted only by the thyroid gland and composes about
75% of the total protein of thyroid follicular colloid. The thyroid hormones thyroxine (T4) and
triiodothyronine (T3) are synthesized from tyrosine residues of Tg in the thyroid epithelial cell. T4 and T3
are released after Tg is endocytosed and proteolytically degraded in the thyrocyte. Tg itself is not
biologically active. Thyroid cancer is commonly treated by surgical removal of the thyroid gland, often
followed by ablation of the thyroid remnant. Patients receive lifelong thyroid hormone replacement
therapy. Traditionally, (131) iodine scanning is used to detect residual disease. More recently, this
approach has been supplemented, and often supplanted, by measurement of serum Tg concentrations.
Serum Tg concentrations are very low or undetectable in athyrotic individuals. In the absence of a
significant thyroid remnant, elevated or rising serum Tg levels are suspicious of recurrent or persistent
disease. It is usually unnecessary to withhold thyroid hormone replacement prior to Tg testing. However,
to optimize the ability to detect recurrent disease, thyroid replacement is often withheld prior to Tg
testing, or recombinant thyrotropin is administered, particularly if the patient also is undergoing (131)
iodine scanning. Thyroid-stimulating hormone (TSH) increases Tg production and iodine uptake of any
benign or malignant residual thyroid tissue.
Useful For: Follow-up of patients with differentiated thyroid cancers after thyroidectomy and ablation
An aid in determining the presence of thyroid metastasis to lymph nodes
Interpretation: Thyroglobulin (Tg) antibody screening is performed to rule out interference in the Tg
assay. Values 10 ng/mL are likely to
have evidence of persistent or recurrent disease. -In athyrotic low-risk thyroid cancer patients, recent
evidence suggests that serum Tg levels