Tg

Thyroglobulin

Immune & Inflammation

What is Thyroglobulin?

Thyroglobulin (Tg) is a large glycoprotein produced exclusively by thyroid follicular cells. It serves as the scaffold for thyroid hormone synthesis: iodine is attached to tyrosine residues on the thyroglobulin molecule within the thyroid follicle, and these iodinated tyrosines are then coupled to form thyroxine (T4) and triiodothyronine (T3). Thyroglobulin is stored in the colloid of thyroid follicles and, when thyroid hormones are needed, it is taken back into the follicular cells, proteolyzed, and T3 and T4 are released into the bloodstream.

In clinical practice, thyroglobulin measurement is most important as a tumor marker for differentiated thyroid cancer (papillary and follicular types) after thyroidectomy and radioiodine ablation. Since thyroglobulin is produced only by thyroid tissue, it should be undetectable or very low after complete thyroid removal. A detectable or rising thyroglobulin level after treatment indicates residual or recurrent thyroid cancer. Thyroglobulin is also elevated in thyrotoxicosis factitia (surreptitious thyroid hormone ingestion), where endogenous thyroid activity is suppressed—a low thyroglobulin in a thyrotoxic patient suggests exogenous hormone intake.

Why It Matters

Thyroglobulin is the primary surveillance marker for differentiated thyroid cancer recurrence after treatment. Thyroid cancer is one of the most curable cancers when detected early, and long-term monitoring with thyroglobulin enables early detection of recurrence—often before it becomes visible on imaging. A rising thyroglobulin triggers further investigation with neck ultrasound and potentially radioiodine scanning. Thyroglobulin antibodies must always be measured alongside thyroglobulin, as they can interfere with the assay and cause falsely low results.

Normal Reference Ranges

GroupRangeUnit
Adults (with intact thyroid)1.5–38.5ng/mL
After total thyroidectomy<0.2ng/mL
After thyroidectomy + ablationUndetectableng/mL

Reference ranges may vary by laboratory. Always compare results to the ranges provided by your testing facility.

What High Tg Levels Mean

Common Causes

  • Differentiated thyroid cancer (papillary, follicular)
  • Thyroid cancer recurrence after treatment
  • Graves disease and toxic nodular goiter
  • Subacute thyroiditis (thyroid destruction releases stored Tg)
  • Endemic goiter (iodine deficiency)
  • Nontoxic multinodular goiter
  • Thyroid injury or biopsy

Possible Symptoms

  • Neck mass or swelling (in thyroid cancer or goiter)
  • Enlarged cervical lymph nodes
  • Hoarseness (recurrent laryngeal nerve involvement)
  • Difficulty swallowing
  • Hyperthyroid symptoms if functional thyroid disease is present
  • Often asymptomatic (detected by surveillance blood test)

What to do: In post-thyroidectomy cancer surveillance: a rising thyroglobulin (even from undetectable to low levels) warrants neck ultrasound and consideration of diagnostic radioiodine whole-body scan. Stimulated thyroglobulin testing (after TSH stimulation via thyroid hormone withdrawal or recombinant TSH injection) increases sensitivity for detecting small-volume recurrence. If structural disease is identified, treatment options include surgical re-excision, radioiodine therapy, or external beam radiation. In patients with an intact thyroid, elevated thyroglobulin is interpreted in the context of thyroid disease (goiter, thyroiditis) and does not by itself indicate cancer.

What Low Tg Levels Mean

Common Causes

  • After successful thyroidectomy and ablation (expected and desired)
  • Thyrotoxicosis factitia (exogenous thyroid hormone ingestion)
  • Overtreatment with levothyroxine (suppressed endogenous production)
  • Thyroglobulin antibody interference (falsely low result)

Possible Symptoms

  • No symptoms from low thyroglobulin itself
  • In thyrotoxicosis factitia: hyperthyroid symptoms with suppressed thyroid gland

What to do: After thyroidectomy for cancer, undetectable thyroglobulin is the goal and indicates excellent response to treatment. Always check thyroglobulin antibodies concurrently—if positive, thyroglobulin levels may be falsely low, and thyroglobulin antibody trends should be used as a surrogate tumor marker instead. In suspected thyrotoxicosis factitia (thyrotoxicosis without thyroid tenderness, low radioiodine uptake, no goiter), a suppressed thyroglobulin confirms exogenous hormone intake.

When Is Tg Testing Recommended?

  • For long-term surveillance after thyroid cancer treatment
  • When thyroid cancer recurrence is suspected
  • When differentiating causes of thyrotoxicosis
  • When evaluating suspected thyrotoxicosis factitia
  • Before and after radioiodine ablation for thyroid cancer

Frequently Asked Questions

Thyroglobulin is produced exclusively by thyroid follicular cells—both normal thyroid tissue and differentiated thyroid cancers (papillary and follicular). After total thyroidectomy and radioiodine ablation, all thyroid tissue should be destroyed, and thyroglobulin should become undetectable. If thyroglobulin later becomes detectable or rises, it means thyroid tissue is present—either residual normal tissue or, more concerning, recurrent cancer. This makes thyroglobulin an extremely sensitive and specific tumor marker for post-treatment surveillance. Patients typically have thyroglobulin measured every 6–12 months for life after thyroid cancer treatment. The American Thyroid Association classifies treatment response based on thyroglobulin levels: "excellent response" is stimulated Tg <1 ng/mL, while "biochemical incomplete response" is stimulated Tg >10 ng/mL.
Thyroglobulin antibodies (TgAb) are autoantibodies directed against thyroglobulin itself. They are present in approximately 25% of thyroid cancer patients and 10% of the general population. TgAb are clinically important because they interfere with thyroglobulin measurement: in immunometric (sandwich) assays (the most commonly used), TgAb cause falsely low thyroglobulin results, potentially masking cancer recurrence. For this reason, TgAb must always be measured alongside thyroglobulin. If TgAb are positive, the thyroglobulin level is unreliable, and the trend of TgAb levels themselves becomes the surrogate marker—rising TgAb suggests cancer recurrence, while declining TgAb suggests remission. Some centers use radioimmunoassay (RIA) methods for thyroglobulin, which may be less affected by TgAb interference.
Stimulated thyroglobulin testing measures thyroglobulin after TSH stimulation, which maximizes thyroglobulin secretion from any remaining thyroid cells (normal or cancerous). TSH stimulation can be achieved two ways: (1) thyroid hormone withdrawal—stopping levothyroxine for 3–4 weeks to allow TSH to rise above 30 mIU/L, which causes hypothyroid symptoms, or (2) recombinant human TSH (rhTSH, Thyrogen) injection—two intramuscular injections on consecutive days, which stimulates thyroglobulin release without causing hypothyroidism. Stimulated thyroglobulin is more sensitive than unstimulated (suppressed) thyroglobulin for detecting small-volume disease. Current guidelines recommend stimulated testing at 6–18 months post-treatment and periodically in intermediate or high-risk patients.

Related Biomarkers

TSHThyroid-Stimulating HormoneFree T4Free ThyroxineFree T3Free TriiodothyronineAnti-TPOTPO Antibodies

Want your Tg levels analyzed?

Upload your lab results for an instant AI-powered breakdown of all your biomarkers.

Upload Lab Results →

Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Reference ranges may vary between laboratories. Always consult your healthcare provider for interpretation of your specific test results.

Disclaimer: SymptomGPT is not a medical diagnosis tool and does not provide medical advice. Always consult a qualified healthcare professional. If you are experiencing a medical emergency, call 911 immediately.