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Thyroglobulin

Tg

Test Codes

Antrim #31438, EPIC: LAB5822, SOFT: THYGG

Department

Special Chemistry

Specimen Collection Criteria

Collect: One Gold-top SST tube. (Minimum Whole Blood: 2.0 mL)

Note: Patient Preparation (Farmington Hills and Royal Oak ONLY): Twenty-four (24) hours before this test, the patient should not take multivitamins or dietary supplements containing biotin (vitamin B7) which is commonly found in hair, skin and nail supplements and multivitamins.

Physician Office/Draw Specimen Preparation

Preparation for Courier Transport

Transport: Centrifuged collection tube, refrigerated (2-8°C or 36-46°F). (Minimum Serum: 0.5 mL)

Rejection Criteria

Plasma specimens. 

Severely lipemic, icteric, or grossly hemolyzed specimens.     

 

In-Lab Processing

Let specimen clot 30-60 minutes then immediately centrifuge to separate serum from cells. Room temperature is acceptable for a maximum of two hours. (Minimum Serum: 0.5 mL)

Storage

Specimen Stability for Testing:

Centrifuged SST Tubes and Microtainers^® with Separator Gels
Room Temperature (20-26°C or 68-78.8°F): 2 hours
Refrigerated (2-8°C or 36-46°F): 72 hours
Frozen (-20°C/-4°F or below): Unacceptable

Red-top Tubes and Microtainers^® without Separator Gels
Room Temperature (20-26°C or 68-78.8°F): 2 hours
Refrigerated (2-8°C or 36-46°F): Unacceptable
Frozen (-20°C/-4°F or below): Unacceptable

Serum Specimens (Pour-Overs)
Room Temperature (20-26°C or 68-78.8°F): 2 hours
Refrigerated (2-8°C or 36-46°F): 72 hours
Frozen (-20°C/-4°F or below): 2 months

Specimen Storage in Department Prior to Disposal:

Refrigerated (2-8°C or 36-46°F): 7 days

Laboratory

Royal Oak Special Testing Laboratory

Performed

Monday – Friday.
Results available within 2 business days.

Reference Range

Less than or equal to 55 ng/mL.

Test Methodology

Chemiluminescent Immunoassay.

Interpretation

When monitoring thyroid cancer patients (post ablation therapy) Thyroglobulin (Tg) concentrations should theoretically be at or below the assay detection limit (0.5 ng/mL). However elevated thyroglobulin antibodies (anti-Tg) are known to interfere with the thyroglobulin measurement in immunometric assays causing a falsely low result. In our Tg assay:

• Thyroglobulin Antibody (anti-Tg) levels of < 21 IU/mL (antibody negative sample) do not affect Tg results.
• Thyroglobulin Antibody (anti-Tg) levels of > 20 IU/mL may suppress thyroglobulin and assay results should be interpreted with caution.

NOTE: We will not perform Tg recovery testing since high Tg recovery (>80%) does not necessarily rule out interference from elevated anti-Tg levels. Monitoring serial Tg levels is often useful in following patients who have been treated for thyroid cancer.

Clinical Utility

Thyroglobulin (Tg) assays are used to monitor patients with thyroid cancer. Patients with localized or metastatic thyroid carcinoma have elevated Tg levels. Tg levels decrease in these patients following complete thyroidectomy and ablation therapy.

Tg levels are elevated in Grave's disease. With successful antithyroid drug therapy Tg levels return to normal. Continued elevated levels of Tg may suggest a future relapse.

Serum Tg levels are also used to differentiate patients with silent (painless) thyroiditis from those with thyrotoxicosis factitia resulting from the surreptitious intake of thyroid hormone.

Serum Tg is elevated in silent thyroiditis and low or normal in thyrotoxicosis factitia. Serum Tg levels are useful in evaluating therapeutic response to treatment of nontoxic diffuse and nodular goiter. Successful treatment is indicated by decreased Tg levels.

CPT Codes

84432, 86800.
LOINC: 3013-0

Contacts

Last Updated

1/13/2023