Familial Dysalbuminemic Hyperthyroxinemia as a Cause for Discordant Thyroid Function Tests

Hyperthyroidism

Thyrotoxicosis causes a variety of symptoms and adverse health outcomes. Hyperthyroidism refers to increased thyroid hormone synthesis and secretion, most commonly from Graves' disease or toxic nodular goitre, whereas thyroiditis (typically autoimmune, viral, or drug induced) causes thyrotoxicosis without hyperthyroidism. The diagnosis is based on suppressed serum concentrations of thyroid-stimulating hormone (TSH), accompanied by free thyroxine and total or free tri-iodothyronine concentrations, which are raised (overt hyperthyroidism) or within range (subclinical hyperthyroidism). The underlying cause is determined by clinical assessment, detection of TSH-receptor antibodies and, if necessary, radionuclide thyroid scintigraphy. Treatment options for hyperthyroidism include antithyroid drugs, radioactive iodine, and thyroidectomy, whereas thyroiditis is managed symptomatically or with glucocorticoid therapy. In Graves' disease, first-line treatment is a 12-18-month course of antithyroid drugs, whereas for goitre, radioactive iodine or surgery are preferred for toxic nodules or goitres. Evidence also supports long-term treatment with antithyroid drugs as an option for patients with Graves' disease and toxic nodular goitre.

Clinical characteristics of familial dysalbuminemic hyperthyroxinemia in Chinese patients and comparison of free thyroxine in three immunoassay methods

OBJECTIVE

Familial dysalbuminemic hyperthyroxinemia (FDH) has not been thoroughly studied in the Chinese population to date. The clinical characteristics of FDH in Chinese patients were summarized, and the susceptibility of common free thyroxine (FT4) immunoassay methods was evaluated.

METHODS

The study included 16 affected patients from eight families with FDH admitted to the First Affiliated Hospital of Zhengzhou University. The published FDH patients of Chinese ethnicity were summarized. Clinical characteristics, genetic information, and thyroid function tests were analyzed. The ratio of FT4 to the upper limit of normal (FT4/ULN) in three test platforms was also compared in patients with R218H ALB mutation from our center.

RESULTS

The R218H ALB mutation was identified in seven families and the R218S in one family. The mean age of diagnosis was 38.4 ± 19.5 years. Half of the probands (4/8) were misdiagnosed as hyperthyroidism previously. The ratios of serum iodothyronine concentration to ULN in FDH patients with R218S were 8.05-9.74 for TT4, 0.68-1.28 for TT3, and 1.20-1.39 for rT3, respectively. The ratios in patients with R218H were 1.44 ± 0.15, 0.65 ± 0.14, and 0.77 ± 0.18, respectively. The FT4/ULN ratio detected using the Abbott I4000 SR platform was significantly lower than Roche Cobas e801 and Beckman UniCel Dxl 800 Access platforms (P < 0.05) in patients with R218H. In addition, nine Chinese families with FDH were retrieved from the literature, of which eight carried the R218H ALB mutation and one the R218S. The TT4/ULN of approximately 90% of patients (19/21) with R218H was 1.53 ± 0.31; the TT3/ULN of 52.4% of patients (11/21) was 1.49 ± 0.91. In the family with R218S, 45.5% of patients (5/11) underwent TT4 dilution test and the TT4/ULN was 11.70 ± 1.33 and 90.9% (10/11) received TT3 testing and the TT3/ULN was 0.39 ± 0.11.

CONCLUSIONS

Two ALB mutations, R218S and R218H, were found in eight Chinese families with FDH in this study, and the latter may be a high-frequency mutation in this population. The serum iodothyronine concentration varies with different mutation forms. The rank order of deviation in measured versus reference FT4 values by different immunoassays (lowest to highest) was Abbott < Roche < Beckman in the FDH patients with R218H.

Thyroid function tests, incongruent internally and with thyroid status, both in a pregnant woman and in her newborn daughter

Introduction

Thyroid function tests (TFT) are extensively used in daily clinical practice. Here, we described a case of incongruent TFT both in a pregnant woman and in her newborn.

Case presentation

A 32-year-old woman, diagnosed with autoimmune thyroiditis during her first pregnancy, was monitored during her second gestation. At week 5 + 2 days, thyroid-stimulating hormone (TSH) and free thyroxine (FT4) values (Dimension VISTA 1500, Siemens Healthineers) were within normal limits. At week 19 + 5 days, TSH remained normal while FT4 increased approximately by three-fold. FT4 inconsistency was with both TSH and the clinical status since she continued to be clinically euthyroid. On the same serum sample, thyroid autoantibodies were negative. At week 25 + 4 days, the patient complained of palpitations and dyspnea, with tachycardia. Even though TSH was normal, high levels of both FT4 and free triiodothyronine (FT3) were interpreted as evidence of thyroid overactivity and methimazole was started. TFT of the pregnant woman continued to be monitored throughout gestation. Postpartum FT4 and FT3 gradually returned to normal. TFT, performed on the daughter's serum, 3 days after birth, showed the same inconsistency as her mother but without clinical signs of congenital hyperthyroidism. Based on the clinical and laboratory setting, the presence of circulating autoantibodies against T3 and T4 (THAb) was suspected and demonstrated by radioimmunoprecipitation.

Conclusion

Analytical interferences should be supposed when TFT do not fit with the clinical picture and despite their infrequency, THAb must also be considered. To our knowledge, this is the first case describing the passage of THAb to the newborn.