Serum thyroglobulin measurements in thyroid cancer: evaluation of 'false' positive results

Clin Endocrinol (Oxf). 1991 Dec;35(6):519-20. doi: 10.1111/j.1365-2265.1991.tb00937.x.


Objective: Serum thyroglobulin (Tg) should be undetectable in patients successfully treated for thyroid carcinoma. We have examined the course of disease in 19 patients with raised serum Tg (greater than 5 micrograms/l) on initial measurement but no other evidence of residual, recurrent or metastatic cancer.

Design: 416 patients from several centres were followed for periods between 1 and 9 years. Serum Tg was measured at 6-12-month intervals.

Patients: All had differentiated thyroid cancer, treated by partial or total thyroidectomy and/or 131I ablation, and were receiving suppressive thyroxine therapy.

Measurement: Serum Tg was measured and clinical, X-ray and scan assessment made of presence or absence of residual, recurrent or metastatic cancer.

Results: Of 416 patients initially assessed, only 19 had Tg greater than 5 micrograms/l but no clinical or radiological evidence of disease. At follow-up, 11 patients had developed overt signs of malignancy; one had been treated with 131I with a subsequent fall in Tg; five had Tg between 5 and 20 micrograms/l with incompletely suppressed TSH levels; two subjects remained with slightly elevated Tg and undetectable TSH.

Conclusion: Patients with elevated Tg require careful follow-up even in the apparent absence of disease. Moderate elevation of serum Tg may be due to inadequate thyroxine suppression therapy, assessed by detectable TSH values measured in a sensitive assay.

MeSH terms

  • Biomarkers, Tumor / blood*
  • False Positive Reactions
  • Follow-Up Studies
  • Humans
  • Thyroglobulin / blood*
  • Thyroid Neoplasms / blood*
  • Thyroid Neoplasms / radiotherapy
  • Thyroid Neoplasms / surgery
  • Thyroidectomy
  • Thyrotropin / blood
  • Thyroxine / therapeutic use


  • Biomarkers, Tumor
  • Thyrotropin
  • Thyroglobulin
  • Thyroxine