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Birte Nygaard, Jens Bentzen, Peter Laurberg, Susanne Møller Pedersen, Lars Bastholt, Aase Handberg, Carsten Rytter, Christian Godballe, and Jens Faber

During follow-up on patients treated for differentiated thyroid cancer, thyroglobulin (Tg) antibodies can interfere with the Tg assay, making the use of Tg less reliable as a tumor marker. Purpose: To compare Tg and Tg autoantibodies (Tg-Ab) methods used in Denmark, regarding the number of patient samples being accepted for evaluating the result of a serum thyroglobulin (s-Tg) measurement. Design: 95 consecutive blood samples drawn from patients in 2006 in one center were selected according to the following criteria: s-Tg <1µg/l and accepted BRAHMS Tg+ recovery test using 50 ng of Tg. Samples were retested with: (1) DPC IMMULITE 2000 Tg and Tg-Ab, (2) BRAHMS Tg and Tg-Ab on Kryptor, (3) BRAHMS Tg+ and Dynotest anti-Tg, (4) DELFIA hTg and recovery test using 25 ng of Tg, and (5) BRAHMS Tg+ with recovery test using 1 and 50 ng of Tg. Results: The number of patient samples that was not accepted for Tg evaluation varied from 2 to 26% when the reference values suggested by the manufacturers of the assay were used. When using the detection limit to the cutoff seen in epidemiological studies the number increased to 40%. Conclusion: We found large discrepancies in acceptance of patient samples for s-Tg evaluation, thus illustrating a diagnostic dilemma.

Open access

Stine Linding Andersen, Niels Henrik Bruun, Peter Astrup Christensen, Simon Lykkeboe, Aase Handberg, Annebirthe Bo Hansen, Maja Hjelm Lundgaard, Louise Knøsgaard, Nanna Maria Uldall Torp, Allan Carlé, Jesper Karmisholt, Inge Bülow Pedersen, Peter Vestergaard, and Stig Andersen

Objective

Thyroid disease in women of reproductive age is mainly of autoimmune origin, and thyroid peroxidase antibodies (TPO-Ab) as well as thyroglobulin antibodies (Tg-Ab) are key markers. Adding to this, much focus in pregnancy is on euthyroid women who are thyroid antibody positive. Evidence to substantiate the cut-offs for the definition of thyroid autoantibody positivity in early pregnant women is warranted.

Methods

Stored serum samples from 14,030 Danish pregnant women were used for the measurement of TPO-Ab, Tg-Ab, TSH, and free thyroxine (ADVIA Centaur XPT, Siemens Healthineers). Among all women, a reference cohort of 10,905 individuals was identified for the establishment of antibody cut-offs. Percentile cut-offs for TPO-Ab and Tg-Ab were determined using regression on order statistics (the reference cohort). The established cut-offs were then applied (the full cohort), and frequencies of early pregnancy as well as later diagnosis of hypothyroidism were evaluated.

Results

The highest established cut-offs (95th, 97.5th, and 99th percentiles) were 59, 68, and 81 U/mL for TPO-Ab and 33, 41, and 52 U/mL for Tg-Ab. When the cut-offs were applied in the full cohort, 11.0, 10.2, and 9.7% were TPO-Ab positive, whereas 13.3, 12.3, and 11.2% were Tg-Ab positive. Antibody-positive women (TPO-Ab and/or Tg-Ab) had higher median TSH and were more likely to have hypothyroidism in early pregnancy and to be diagnosed with hypothyroidism during follow-up.

Conclusions

This large study established and evaluated pregnancy-specific cut-offs for TPO-Ab and Tg-Ab. The findings are important regarding the classification of exposure in pregnancy and assessment of thyroid autoimmunity per se.