Thyroglobulin

Notes

• Thyroglobulin (Tg) should only be requested for the evaluation and management of patients treated for thyroid cancer with surgery and radioiodine and who are established on thyroid hormone replacement.
• Measurement of thyroglobulin is of no value in the diagnosis of thyroid cancer.
• Thyroglobulin assays are not reliable in the presence of thyroglobulin antibodies. Samples will be routinely screened for these antibodies when thyroglobulin is requested.
• Thyroglobulin levels within 3 months of thyroid surgery or ablation will be difficult/impossible to interpret.

Sample requirements

For adults, 5 ml of blood taken into a narrow gold top tube (or rust top for the Acute Unit).

Storage/transport

Send at ambient temperature to the laboratory. If unavoidable, samples can be stored refrigerated overnight.

Required information

Relevant clinical details including details of thyroid surgery, treatment and thyroid replacement therapy.

Turnaround times

Samples are processed locally, once a week.

Reference ranges

• A serum Tg of <0.1 µg/l while on suppressive levothyroxine therapy, has a negative predictive value for recurrent or persistent thyroid cancer of >98%. In selected patients (low risk cases), a serum Tg <0.1 may obviate the need for assessing serum Tg under TSH stimulation.
• A serum Tg >0.1 µg/L while on suppressive levothyroxine therapy may indicate thyroid remnant, recurrent or persistent disease. Depending on individual circumstances such patients may require further investigation or monitoring for a trend in serum Tg over time before further action.
• Thyroglobulin antibody levels > 20 KU/L could potentially cause interference in the current thyroglobulin assay.

Further information

To learn more about thyroglobulin visit Lab Tests Online.