Thyroglobulin

Diagnostic Use

Serum thyroglobulin (Tg) is increased in thyroiditis, goitre, thyroid trauma, hyperthyroidism, and thyroid carcinomas. Because elevated levels of Tg are non-specific it is not useful in the initial diagnosis of malignancy, but is useful in detection of recurrence (see below).

It is important to take the baseline specimen before a fine needle aspiration biopsy is performed. Damage to the thyroid gland may elevate Tg concentrations for at least 3 weeks. Surgery will elevate the concentration of thyroglobulin for at least two months; there is little value in collecting specimens for post-operative monitoring before then.

Following combination surgery and radioiodine ablation of thyroid carcinoma, serum Tg can be used to monitor recurrence, if the tumour originally secreted thyroglobulin .  The sensitivity of Tg as a marker of recurence is increased by TSH stimulation, which can be achieved either by thyroxine withdrawal or by administration of recombinant human TSH.  Guidelines have recommended that a serum Tg of greater than 2 ug/L  (ref 1) or any detectable Tg (ref 2) after stimulation should prompt further investigation.  Note that not all differentiated thyroid cancers secrete thyroglobulin, therefore it is important to know whether the pre-operative thyroglobulin was raised or not.

Inter-laboratory variation : significant variation exists between Tg assay methods.  To ensure comparability, serial Tg measurements should be performed by the same laboratory.

References:
1. Mazziferri et al. A consensus report of the role of serum thyroglobulin as a monitoring method for low-risk patients with papillary thyroid carcinoma. J Clin Endocrinol Metab. 2003; 88: 1433-41.

2. Pacini F, Schlumberger M, Dralle H et al. European consensus for the management of patients with differentiated thyroid carcinoma of the follicular epithelium. Eur J Endocrinol. 2006;154:787-803

Reference Intervals

NOTE:  It is important to take the baseline specimen before a fine needle aspiration biopsy is performed. Damage to the thyroid gland may elevate thyroglobulin concentrations for at least 3 weeks.

Units: ug/L

• Anti-thyroglobulin antibodies are often present in patients. These antibodies may interfere with the thyroglobulin measurement, causing falsely low and even  undetectable results.