E.F.E. Wenstedt1, J.J.G. Hillebrand2, J.A.P. Bons3, S.A.A. van den Berg1,4
1 Department of Clinical Chemistry, Erasmus MC, Rotterdam, The Netherlands
2 Department of Laboratory Medicine, Amsterdam UMC, Amsterdam, The Netherlands
3 Central Diagnostic Laboratory, Maastricht UMC+, Maastricht, The Netherlands
4 Department of Internal Medicine, Erasmus MC, Rotterdam, The Netherlands
Introduction
In the Netherlands, thyroid cancer has an incidence of >800 per annum, mostly comprised of papillary and follicular carcinoma. Laboratory assessment of thyroglobulin (Tg) and thyroglobulin antibodies (Tg-ab) are pivotal in risk stratification and follow-up after primary treatment.
Post-thyroidectomy and ablation, excellent response is defined as negative imaging combined with low Tg where interference by Tg-ab can be excluded. When Tg-ab are stable or decreasing, risk stratification changes to inconclusive, and increasing Tg-ab define a biochemically insufficient response.
Therefore, it is crucial to have knowledge on interference of Tg-ab in Tg measurements, and the definition for their increase or decrease.
Methods
Together with the SKML Endocrine section, we organized a nationwide survey to gain insight in the state-of-art in analysis and interpretation of Tg en Tg-ab, in the context of thyroid cancer.
Results
56 laboratories completed the survey, of which 16 performed Tg and Tg-ab measurements in context thyroid carcinoma. “Positive” Tg-ab cut-offs varied between biochemical thresholds (LOD to ULN), self-defined cut-offs or were also left to decision by the requesting physician. Only 1 laboratory performed delta-checks for changes in Tg-ab. Interestingly, 9 laboratories (>50%) had no knowledge on possible Tg-ab interference and 4 laboratories used literature references without experimental data. Only 3 laboratories used original experimental data.
Conclusion
In the Netherlands, there is no consensus on Tg and Tg-ab reports and interpretation. In addition, although crucial, over 80% of Dutch clinical laboratories had no experimental data on interference of Tg-ab on Tg measurements. These discrepancies may result in incorrect risk-stratification of patients with differentiated thyroid carcinoma.