Unexpected elevated free thyroid hormones in pregnancy.

Unexpected elevated free thyroid hormones in pregnancy.

Thyroid. 2016 Aug 18;

Authors: Teti C, Nazzari E, Galletti M, Mandolfino MG, Pupo F, Pesce G, Lillo F, Bagnasco M, Benvenga S

Abstract
BACKGROUND: The use of thyrotropin and free thyroid hormone assays to evaluate thyroid function is widespread, but in some situations the results are inconsistent with the patient's thyroid status.
SUMMARY: A 35-year-old woman with a known diagnosis of chronic autoimmune thyroiditis was referred to us at week 26 of her second pregnancy. The patient was clinically euthyroid; consistent with this, her serum TSH was normal (0.79 mU/L), but she had elevated free thyroid hormones (fT3, fT4), as determined by a one-step chemiluminescent assay. The patient was taking levothyroxine replacement therapy (125 µg/d) and the dose was confirmed. Previous blood tests showed concordance between TSH and free thyroid hormone values. We followed up the patient throughout gestation and 12 months postpartum. During gestation, her free thyroid hormones remained high using one-step methods, while the total thyroid hormone concentration were within the reference range, in agreement with the TSH values. Post partum fT4 and fT3 values returned progressively to normality, in agreement with the TSH values. We hypothesized the presence of circulating thyroid hormone autoantibodies (THAb), which are known to interfere, although to a variable extent, with thyroid hormone one-step assays. Using stored frozen sera, we were able to confirm this hypothesis indirectly by measuring normal levels of FT3 and FT4 with a two-step method, and directly by demonstrating THAb against the two hormones.
CONCLUSIONS: Despite their relative rarity, circulating THAb may be suspected when laboratory data are not consistent and contrast with the clinical picture. To our knowledge, no previous case of transient appearance of THAb in pregnancy has been described.

PMID: 27538922 [PubMed - as supplied by publisher]

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