Lab Dept:

Chemistry

Test Name:

THYROGLOBULIN TUMOR MARKER

General Information

Lab Order Codes:

TG

Synonyms:

HTG; TATC (Thyroglobulin Assay for Thyroid Cancer); TG; Thyroglobulin HTG; Thryoglobulin Antibody Screen

CPT Codes:

84432 – Thyroglobulin, tumor marker

Test Includes:

Includes Thyroglobulin Tumor Marker reported in ng/mL and Anti-thyroglobulin Antibody reported in IU/mL.

Logistics

Test Indications:

Follow-up of patients with differentiated thyroid cancers after thyroidectomy and ablation. As an aid in determining the presence of thyroid metastasis to lymph nodes.

Lab Testing Sections:

Chemistry - Sendouts

Referred to:

Mayo Medical Laboratories (Test# 23745)

Phone Numbers:

Minneapolis:

Saint Paul:

612-813-6280

651-220-6550

Test Availability:

Daily, 24 hours

Turnaround Time:

1 - 3 days, test set up Monday through Saturday

Special Instructions:

N/A

Specimen

Specimen Type:

Blood

Container:

Red top tube

Draw Volume:

4.5 mL (Minimum: 3 mL) blood

Processed Volume:

1.5 mL (Minimum: 1 mL) serum

Collection:

Routine venipuncture

Special Processing:

Lab Staff: Centrifuge specimen, remove serum aliquot into a screw-capped round bottom plastic vial. Store and ship at refrigerated temperatures. Forward promptly.

Patient Preparation:

None

Sample Rejection:

Gross hemolysis, mislabeled or unlabeled specimens

Interpretive

Reference Range:

Thyroglobulin Tumor Marker:

≥16 years: < or = 33 ng/mL (normal thyroid)
OR
< or = 2 ng/mL (athyrotic patients)

Thyroglobuln Antibody

All ages: <22 IU/mL

Thyroglobulin (Tg) antibody screening is performed to rule out interference in the Tg assay. Values <22 IU/mL are considered normal and unlikely to cause interference.

All of the following interpretive suggestions for serum Tg apply to patients who do not have elevated serum Tg autoantibodies.

The American Thyroid Association guidelines for the management of differentiated thyroid cancer suggest that athyrotic thyroid cancer patients (total thyroidectomy and radioiodine remnant ablation) should have unstimulated (on T4) and stimulated (thyroid hormone withdrawl or recombinant human TSH stimulation) serum Tg concentrations < or = 2 ng/mL. Patients with highter levels should be investigated for persistent or recurrent disease.

Athyrotic thyroid cancer patients with unstimulated or stimulated serum Tg concentrations >10 ng/mL are likely to have evidence of tumor recurrence.

In athyrotic low-risk thyroid cancer patients, recent evidence suggests that serum Tg levels <0.1 ng/mL, combined with neck ultrasound, oviate the need for stimulated Tg testing.

For patients with small thyroidal remnants there are currently no universally accepted cutoff levels for Tg. It has been suggested that Tg levels should not exceed approximately 0.5 ng/mL per gram of remnant tissue in patients with suppressed TSH (<0.3 mIU/L), or approximately 1 ng/mL if TSH is in the normal reference range.

Critical Values:

N/A

Limitations:

The test is most sensitive for detection of thyroid cancer recurrence when patients are off thyroid replacement long enough to have an elevated TSH prior to drawing the specimen. This test also can be used to follow patients with normal TSH; however, Tg values from specimens with high TSH should not be compared with values with normal TSH, because TSH stimulation changes the baseline determinations.

Thyroid autoantibodies may interfere with the measurement of Tg. All specimens are prescreened for antibodies and a comment appended to the report if they are present. Undetectable levels of Tg should be interpreted with caution if anti-Tg is present. A Tg antibody result of <22 IU/mL is unlikely to cause clinically significant Tg assay interference. It is recommended that the thyroglobulin result be reviewed for concordance with clinical presentation.

Specimens with Tg concentrations >250,000 ng/mL may hook and appear to have markedly lower values.

Anti-Tg values determined by different methodologies might vary significantly and cannot be directly compared with one another. Some patients might show to be antibody-positive by some methods and antibody-negative by others. Comparing anti-Tg antibodies values from different methods might lead to erroneous clinical interpretation.

In patients receiving therapy with high biotin doses (ie, >5 mg/day), no specimen should be drawn until at least 8 hours after the last biotin administration.

Tg concentrations >2,000 ng/mL may lead to falsely elevated anti-Tg concentrations.

Methodology:

Thyroid Tumor Marker: Immunoenzymatic Assay
Anti-Thyroid Antibody: Electrochemiluminescence Immunoassay

References:

Mayo Medical Laboratories Web Page (April 2011)

Updates:

4/6/2004: Test code at Mayo changed. Test name changed from Thyroglobulin to Thyroglobulin Tumor Marker.

9/20/2006: Thyroglobulin Ab reference range previously reported as ≤2.3 IU/mL.

1/23/2008: Note change in Thyroglobulin Screening Reference range.

10/5/2010: Note new athyrotic reference values.

1/27/2011: Due to reagent issues at MML for Thyroglobulin Ab, the Tumor Marker battery no longer screens for this test. A separate order to Antithyroglobulin Ab must be ordered and will be forwarded to Quest Diagnostics.

4/12/2011: Mayo has validated a new Anti-thyroglobulin Ab test and has added it back to this test. Please note the new method and reference range. Testing is now all performed at Mayo.