Thyroglobulin Cutoff Values for Detecting Excellent Response to Therapy in Patients With Differentiated Thyroid...

Area of Science:

• Endocrinology
• Oncology
• Clinical Chemistry

Background:

• Serum thyroglobulin (Tg) is a key biomarker for monitoring differentiated thyroid carcinoma (DTC) after thyroidectomy.
• Tg can detect persistent or recurrent DTC before structural disease (SD) is evident on imaging.

Purpose of the Study:

• To evaluate the Elecsys® Tg II assay's performance at a 0.2 ng/mL cutoff for ruling out SD in adults with DTC post-thyroidectomy.
• To assess the assay's utility with or without radioiodine ablation (RAI).

Main Methods:

• Two patient cohorts were used: longitudinal (Tg assessed bi-annually for 2 years under TSH suppression) and cross-sectional (Tg assessed once in patients with confirmed SD).
• Analyses were conducted on combined cohorts and the longitudinal cohort, including RAI-treated and non-RAI-treated subgroups.

Main Results:

• The Elecsys Tg II assay with a 0.2 ng/mL cutoff demonstrated a 99.9% negative predictive value for ruling out SD.
• The assay showed high sensitivity (98.5%-100%) and acceptable specificity (53.4%-53.5%) for detecting SD.
• Performance was consistent across both cohorts and in RAI-treated versus non-RAI-treated patients.

Conclusions:

• A Tg cutoff of 0.2 ng/mL is highly effective for excluding SD in post-thyroidectomy DTC patients under TSH suppression.
• This cutoff is reliable even in patients who have not undergone RAI treatment, supporting its clinical utility.