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HelpTest Code TGAB Thyroglobulin Antibody, Serum
Reporting Name
Thyroglobulin Antibody, SUseful For
As an adjunct in the diagnosis of autoimmune thyroid diseases: Hashimoto disease, postpartum thyroiditis, neonatal hypothyroidism, and Graves disease
Method Name
Immunoenzymatic Assay
Performing Laboratory
Mayo Clinic Laboratories in Rochester
Specimen Type
Serum RedOrdering Guidance
For the follow-up of patients with differentiated follicular cell-derived thyroid carcinomas, consider either HTG2 / Thyroglobulin, Tumor Marker, Serum or HTGR / Thyroglobulin, Tumor Marker Reflex, Serum.
The preferred method for confirming Graves disease in atypical cases or under special clinical circumstances is measurement of the pathogenic antithyrotropin receptor antibodies by binding assay or bioassay. Order either THYRO / Thyrotropin Receptor Antibody, Serum or TSI / Thyroid-Stimulating Immunoglobulin, Serum.
Specimen Required
Patient Preparation: For 12 hours before specimen collection, do not take multivitamins or dietary supplements containing biotin (vitamin B7), which is commonly found in hair, skin, and nail supplements and multivitamins.
Container/Tube: Red top (gel tubes/SST are not acceptable)
Specimen Volume: 0.6 mL
Collection Instructions: Centrifuge and aliquot serum within 2 hours of collection.
Specimen Minimum Volume
0.5 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Serum Red | Refrigerated (preferred) | 7 days | |
| Frozen | 30 days | ||
| Ambient | 7 days |
Reject Due To
| Gross hemolysis | Reject |
| Gross lipemia | OK |
| Gross icterus | Reject |
Reference Values
<4.0 IU/mL
Reference values apply to all ages.
Day(s) Performed
Monday through Saturday
CPT Code Information
86800
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| TGAB | Thyroglobulin Antibody, S | 56536-6 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| TGAB | Thyroglobulin Antibody, S | 56536-6 |
Clinical Information
Thyroglobulin autoantibodies bind thyroglobulin (Tg), a major thyroid-specific protein. Tg plays a crucial role in thyroid hormone synthesis, storage, and release.
Tg is not secreted into the systemic circulation under normal circumstances. However, follicular destruction through inflammation (thyroiditis and autoimmune hypothyroidism), hemorrhage (nodular goiter), or rapid disordered growth of thyroid tissue, as may be observed in Graves disease or follicular cell-derived thyroid neoplasms, can result in leakage of Tg into the blood stream. This results in the formation of autoantibodies to Tg (anti-Tg) in some individuals. The same processes also may result in exposure of other "hidden" thyroid antigens to the immune system, resulting in the formation of autoantibodies to other thyroid antigens, in particular thyroid peroxidase (TPO) (anti-TPO). Since anti-Tg and anti-TPO autoantibodies are observed most frequently in autoimmune thyroiditis (Hashimoto disease), they were originally considered to be of possible pathogenic significance in this disorder. However, the consensus opinion today is that they are merely disease markers. It is felt that the presence of competent immune cells at the site of thyroid tissue destruction in autoimmune thyroiditis simply predisposes the patient to form autoantibodies to hidden thyroid antigens.
In individuals with autoimmune hypothyroidism, 30% to 50% will have detectable anti-Tg autoantibodies, while 50% to 90% will have detectable anti-TPO autoantibodies. In Graves disease, both types of autoantibodies are observed at approximately half these rates.
The presence of anti-Tg, which occurs in 15% to 30% of thyroid cancer patients, could result in misleading Tg results. In immunometric assays, the presence of thyroid antibody can lead to false-low measurement, whereas it might lead to false-high results in competitive assays.
Interpretation
Diagnosis of Autoimmune Thyroid Disease:
Measurements of antithyroperoxidase (anti-TPO) have higher sensitivity and equal specificity to antithyroglobulin (anti-Tg) measurements in the diagnosis of autoimmune thyroid disease. Anti-Tg levels should, therefore, only be measured if anti-TPO measurements are negative but clinical suspicion of autoimmune thyroid disease is high.
Detection of significant titers of anti-Tg or anti-TPO autoantibodies is supportive evidence for a diagnosis of Graves disease in patients with thyrotoxicosis. However, measurement of the pathogenic antithyrotropin receptor antibodies by binding assay (THYRO / Thyrotropin Receptor Antibody, Serum) or bioassay (TSI / Thyroid-Stimulating Immunoglobulin, Serum) is the preferred method of confirming Graves disease in atypical cases and under special clinical circumstances.
Positive thyroid autoantibody levels in patients with high-normal or slightly elevated serum thyrotropin levels predict the future development of more profound hypothyroidism.
Patients with postpartum thyroiditis with persistently elevated thyroid autoantibody levels have an increased likelihood of permanent hypothyroidism.
In cases of neonatal hypothyroidism, the detection of anti-TPO or anti-Tg in the infant suggests transplacental antibody transfer, particularly if the mother has a history of autoimmune thyroiditis or detectable thyroid autoantibodies. The neonatal hypothyroidism is likely to be transient in these cases.
Cautions
Low titers of thyroid autoantibodies may be observed in the absence of autoimmune or other thyroid diseases and are considered a nonspecific finding. The population prevalence of such nonspecific low-level antithyroglobulin (antiTg) positivity is higher in female patients than in male patients and increases with age in both sexes.
Patients with nodular thyroid disease who are antithyroid autoantibody positive may have coexisting Hashimoto disease, which can result in a suspicious fine-needle aspiration biopsy diagnosis of follicular or Hurthle cell neoplasia.
Anti-Tg and antithyroperoxidase (anti-TPO) 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 and anti-TPO values from different methods might lead to erroneous clinical interpretation.
In rare cases, some individuals can develop antibodies to mouse or other animal antibodies (often referred to as human anti-mouse antibodies [HAMA] or heterophile antibodies), which may cause interference in some immunoassays. Caution should be used in interpretation of results, and the laboratory should be alerted if the result does not correlate with the clinical presentation.
Method Description
The Access Thyroglobulin Antibody II assay (TgAb) is a sequential 2-step immunoenzymatic (sandwich) assay. A sample is added to a reaction vessel with paramagnetic particles coated with the thyroglobulin protein. The serum TgAb binds to the thyroglobulin. After incubation in a reaction vessel, materials bound to the solid phase are held in place by a magnetic field, while unbound materials are washed away. The thyroglobulin-alkaline phosphatase conjugate is added and binds to the TgAb. After the second incubation, materials bound to the solid phase are held in place by a magnetic field, while unbound materials are washed away. Then, the chemiluminescent substrate is added to the reaction vessel, and light generated by the reaction is measured with a luminometer.(Package insert: Access Thyroglobulin Antibody II. Beckman Coulter Inc; 04/2020)