New-generation thyroglobulin assay: performance and implications for follow-up of differentiated thyroid carcinoma

Differentiated thyroid cancer (DTC) requires long-term follow-up by serum thyroglobulin assay and cervical ultrasound, due to the risk of recurrence. Guidelines recommend basal assay under hormone therapy at 3 months, repeated at 6-12 months post-surgery, with or without associated isotopic ablation, after stimulation by recombinant human TSH to improve assay sensitivity. It was hypothesized that a new-generation assay kit with lower limits of detection and quantification would improve the sensitivity of the basal assay, enhance detection of premature recurrence and decrease the rate of false-negatives, thereby avoiding the need for the complementary stimulation test.

A validation study of the second-generation thyroglobulin serum assay was performed in the laboratory of the Lyon Sud Hospital Centre (Lyon, France), with comparison to stimulation test results. Low-concentration serum pools were constituted, including patients followed for stage I to III DTC for whom basal and post-stimulation samples were available in the serum bank.

The new assay proved robust and reliable, with good correlation with the technique presently used in the Lyon hospitals. None of the 54 patients showed false-negative results, which was the objective of our choice of threshold, and 5 were false-positive, for thyroglobulin thresholds of 0.1μg/L at baseline and 1.0μg/L post-stimulation. Positive and negative predictive values were 100% and 87.8% respectively.

These results allow an improvement in the follow-up algorithm for DTC, replacing the stimulation test by the new-generation thyroglobulin assay in post-therapeutic assessment.