[The value of a new IRMA for determining thyroglobulin]

Area of Science:

• Endocrinology
• Oncology
• Clinical Chemistry

Background:

• Differentiated thyroid carcinoma (DTC) management relies on monitoring thyroglobulin (Tg) levels.
• Traditional radioimmunoassay (RIA) for Tg has limitations in sensitivity and specificity.
• A novel immunoradiometric assay (IRMA) system for Tg determination has been developed.

Purpose of the Study:

• To compare the performance of a new Tg-IRMA system with the established Tg-RIA method.
• To evaluate the clinical relevance of Tg-IRMA in patients with differentiated thyroid carcinoma.
• To assess the impact of various preanalytical factors on Tg determination using Tg-IRMA.

Main Methods:

• Parallel serum Tg determinations were performed using Tg-IRMA and Tg-RIA in 277 DTC patients.
• Intra- and interassay variations were assessed for the Tg-IRMA system.
• The influence of serum sample handling (freezing, hemolysis, lipemia, dilution, serum separator tubes) was examined.

Main Results:

• Tg-IRMA demonstrated lower intra- and interassay variations at higher Tg concentrations (3% and 6% for >40 ng/ml).
• Preanalytical factors showed no significant practical relevance for clinical routine use of Tg-IRMA.
• In patients with no residual thyroid tissue, Tg-IRMA achieved 99% sensitivity and 90% specificity at a 1 ng/ml cutoff, outperforming Tg-RIA (89% sensitivity, 95% specificity at 10 ng/ml).

Conclusions:

• The Tg-IRMA system is significantly more sensitive than Tg-RIA for detecting residual thyroid tissue and monitoring remission in DTC patients.
• Tg-IRMA offers improved accuracy in Tg determination, crucial for effective patient management.
• A clinical significance cutoff of 1 ng/ml and a grey-zone of 1-3 ng/ml were defined for Tg-IRMA in routine clinical practice.