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Test Name:
Thyroglobulin with Thyroglobulin Antibodies
- SBMF No:
30022 - Performance Lab Name:
Manual Lab - Test Mnemonic:
THYRO W/AB - ABN:
Not required - CPT Code:
84432; 86800 - LOINC Code:
3013-0; 8098-6 - Test Includes:
Thyroglobulin
Thyroglobulin Antibodies - Also Known As:
Human Thyroglobulin (HTG)
Tg with Tg Ab
Thyroglobulin Assay for Thyroid Cancer (TATC)
Thyroglobulin Panel
Thyroglobulin Tumor Marker - Also See:
30020 Thyroglobulin Antibodies - Spec Type:
Serum - Spec Container:
Gold top (SST) or red top (serum) tube - Alt Spec Type:
Plasma - Alt Spec Container:
Green top (lithium heparin) tube - Pref Vol:
1.0 mL - Min Vol:
0.5 mL - Fasting:
No - Spec Collect:
Routine venipuncture - Spec Process:
Clot 30 minutes
Promptly centrifuge 15 minutes
Immediately transfer serum to separate plastic tube - Spec Store Transport:
Refrigerated - Spec Stability:
1 week refrigerated (2-8°C)
2 months frozen (-20°C) – Do not use frost-free units that undergo repeated freeze/thaw cycles - Spec Reject:
Hemolyzed sample - Methodology:
Chemiluminescent Immunoassay (CLIA) - Use:
The follow-up, but not the diagnosis, of patients with well-differentiated thyroid cancer (DTC) - Clinical Significance:
Thyroglobulin is a 660,000 MW dimeric glycoprotein composed of two identical subunits. The monomeric peptide moiety is composed of 2748 amino acids, and contains 8-10% carbohydrate and iodine. The amount of iodine varies with the dietary intake of the individual. Thyroglobulin (TG) is normally synthesized and secreted by follicular cells of the thyroid gland, and its rate of synthesis is controlled by TSH. Tg and Tg mRNA is present in the serum of all euthyroid individuals. Normal serum Tg reference limits are approximately 4-40 ng/mL based on CRM-457 standardized immunoassays. The thyroid hormones thyroxine (T4) and 3,5,3’-triiodothyronine (T3) are synthesized from tyrosine residues on thyroglobulin within the thyroid epithelial cell. Thyroglobulin itself is not biologically active, and comprises about 75% of the total protein of the thyroid follicular colloid (lumen).Three factors determine serum Tg concentrations in most clinical situations: (1) thyroid cell mass; (2) physical damage to the thyroid caused by biopsy, surgery, obstructive asphyxia, hemorrhage, radioiodine administration, external irradiation, or inflammation; and (3) activation of TSH-receptors by either TSH, chorionic gonadotropin (HCG) during pregnancy, or thyroid stimulating immunoglobulins of Graves disease. With sufficiently sensitive assays, a below normal serum Tg is rarely encountered except in those patients who have had total or near-total thyroidectomy, thyroid ablation by radioiodine, or in whom TSH secretion is suppressed by exogenous thyroid hormone administration. Patients with other thyroid disorders typically have normal or high normal serum Tg concentrations, with high levels associated with autonomous thyroid function, thyroid injury, or activation of TSH receptors. For these reasons and the frequent presence of Tg autoantibodies, a serum Tg measurement seldom provides any increase in specificity in the differential diagnosis of thyroid disorders.The major clinical use of serum Tg measurements is the follow-up, but not the diagnosis, of patients with well-differentiated thyroid cancer (DTC). Serum Tg concentrations are increased in patients with both benign and DTC, and do not serve to distinguish between the two. After all cancerous thyroid tissue has been removed by surgery, radioiodine therapy, or other ablative procedures, serum Tg measurements serve as a marker in the determination of residual or recurrent metastatic tissue of thyroid origin. In this context, serum Tg measurements reflect the sum of three variables: (1) the mass of DTC remaining; (2) the ability of the remaining tumor and thyroid tissue to respond to either endogenous TSH or recombinant human TSH (rhTSH) stimulation; and (3) the intrinsic ability of the tumor to synthesize and secrete TG.The accurate measurement of serum Tg in the presence of Tg autoantibodies (TgAb) is technically challenging. TgAb interference may cause either over-estimation or under-estimation of TgAb positive sera by current methods. With competitive binding assays such as radioimmunoassays, TgAb interference generally produces over-estimated Tg results. With immunometric assays [sandwich assays], TgAb interference typically produces inappropriately low Tg results, most likely caused by endogenous Tg immune complexes that block one or more of the reagent antibodies from binding endogenous Tg. - Reference Range:
Thyroglobulin (normal thyroid): Less than or equal to 55 ng/mL
Thyroglobulin Antibodies: Less than or equal to 40 IU/mL - Additional Test Info:
Notes: Recombinant human thyroid-stimulating hormone (rhTSH) has been shown to stimulate thyroid cells to release thyroglobulin, and to significantly increase Tg test sensitivity over Tg testing while the patient is on thyroid hormone therapy. Serum Tg levels after rhTSH administration may be lower than serum Tg levels after thyroid hormone withdrawal. A possible reason for the lower Tg results using rhTSH is that acute stimulation with rhTSH may not elicit the same thyroglobulin response as compared to stimulation with endogenous TSH during thyroid hormone withdrawal. During thyroid hormone withdrawal, the patient is subjected to a longer period of TSH stimulation. - Day Run:
Mon, Wed, Fri - Time Run:
8:00 am - Time Reported:
3:30 pm - Test Type:
TUMOR MARKER
