Thyroglobulin Antibodies (Autoimmune Thyroiditis)
Label Mnemonic: TGAB
Epic Lab Code: LAB956
Downtime Form: A-1a General Laboratory Requisition
Chemistry
6240 RCP
356-3527
Specimen(s):
Plasma
Collection Medium:
Pink top tube 6 mL (K2-EDTA)
Alternate Collection Media:
Red top tube 5 mL (Clot Activator)
Minimum:
3 mL whole blood in pink top tube or TWO Microtainer® devices.
Testing Schedule:
24 hrs/day, 7 days a week, including holidays.
Turn Around Time:
1 hour (upon receipt in laboratory)
Reference Range:
<116 IU/mL

Reference values apply to all ages.
Interpretive Data:
Diagnosis of Autoimmune Thyroid Disease:
Measurements of anti-thyroid peroxidase (anti-TPO) autoantibodies have higher sensitivity and equal specificity to anti-thyroglobulin (anti- Tg) autoantibody measurements in the diagnosis of autoimmune thyroid disease. Anti-Tg autoantibody levels should, therefore, only be measured if anti-TPO autoantibody measurements are negative, but clinical suspicion of autoimmune thyroid disease is high.

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 autoantibodies 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.

Thyroid Cancer Follow-Up:
Following therapy of differentiated follicular-cell derived thyroid cancer, all patients who have no, or only trivial, amounts of normal residual thyroid tissue and no persistent or recurrent cancer will have undetectable or very low serum thyroglobulin (Tg) levels. Persistently elevated or rising serum Tg levels, either on or off thyroxine replacement therapy, suggest possible tumor persistence or recurrence. However, if a patient also has measurable anti-Tg autoantibody levels >= 22 IU/mL, the results of serum Tg measurements are unreliable. Anti-Tg autoantibodies may result in both falsely-low and, less commonly, falsely-high serum Tg measurements. Therefore, in anti-Tg-positive patients, serum Tg measurements should either not be used in thyroid cancer follow-up or be interpreted with extreme caution. A thyroglobulin antibody result of <22 IU/mL is unlikely to cause clinically significant thyroglobulin assay interference. It is recommended that the thyroglobulin result be reviewed for concordance with clinical presentation.
Comments:
Useful for an adjunct to anti-thyroid peroxidase (anti-TPO) autoantibody, antithyrotropin-receptor autoantibody, and thyroid- stimulating immunoglobulin measurements in the diagnosis of autoimmune thyroid diseases: Hashimoto disease, postpartum thyroiditis, neonatal hypothyroidism, and Graves disease.

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 anti- thyroglobulin (anti-Tg) positivity is higher in females than in males and increases with age in both genders.

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.
Test Limitations:
Hemolysis: No significant interference up to an H index of 1690 (approximate hemoglobin concentration: 1690 mg/dL).

Lipemia: No significant interference up to an L index of 2000 (approximate triglycerides concentration: 4000 mg/dL). Note there is poor correlation between turbidity and triglyceride concentration.

Icterus: No significant interference up to an I index of 66 (approximate conjugated and unconjugated bilirubin concentration: 66 mg/dL).
Methodology:
Electrochemiluminescence Immunoassay
CPT Code:
86800