Thyroid hormone autoantibodies and their implications for free thyroid hormone measurement

Characterisation of an interference affecting the triiodothyronine measurement on two different immunoassays

We report a case of falsely elevated triiodothyronine (T3) due to anti-T3 antibody interference in two immunoassays (Cobas 8000 e602® module (Roche Diagnostics) and Architect® i2000 (Abbott)). The interference was investigated using various laboratory methods including the search for heterophilic antibodies, biotin detection and the polyethylene glycol precipitation of potential interfering macromolecules. The presence of anti-T3 autoantibodies was detected and measured by radioimmunoprecipitation. Our investigations confirmed the clinical suspicion of a falsely elevated free T3. No further explorations or unnecessary treatments were conducted for this patient after identification of the interference. This underlines the importance of implementing systematic analytical procedures in laboratories for the search of suspected interferences.

Avoiding Misdiagnosis Due to Antibody Interference with Serum Free Thyroxin

INTRODUCTION

Interfering antibodies are capable of causing potentially misleading results in automated thyroid hormone immunoassays.

CASE PRESENTATION

We report the case of a 46- year-old female patient with autoimmune hypothyroidism in chronic replacement treatment with levothyroxine who was presented 8 years after diagnosis with a thyroid function test showing an increased level of TSH and a very high level of FT4. Interference in the laboratory serum free thyroxin (FT4) test was suspected, due to the lack of symptoms of hyperthyroidism and a different immunoassay platform confirmed a low FT4 result. The discrepancy between the two results was explained by the presence of antiT4-autoantibodies.

CONCLUSIONS

Antibody interference with serum free thyroxine must be considered when clinical findings and laboratory results show discrepancies.

The clinical use of thyroid function tests

Laboratory tests are essential for accurate diagnosis and cost-effective management of thyroid disorders. When the clinical suspicion is strong, hormonal levels just confirms the diagnosis. However, in most patients, symptoms are subtle and unspecific, so that only biochemical tests can detect the disorder. The objective of this article is to do a critical analysis of the appropriate use of the most important thyroid function tests, including serum concentrations of thyrotropin (TSH), thyroid hormones and antithyroid antibodies. Through a survey in the MedLine database, we discuss the major pitfalls and interferences related to daily use of these tests and recommendations are presented to optimize the use of these diagnostic tools in clinical practice.

Dysthyronemia in normal concentrations of thyrotropin--analytical and clinical consequences

This article discusses the conditions that may lead to a phenomenon called dysthyronemia. Here, the thyroid gland has concentration of thyrotropin in circulation within the reference range, but the concentrations of free or total fractions of thyroid hormones are outside the reference range. Normal values of thyrotropin (TSH) and increased values of THs are referred to as hyperthyroxinemia, while normal values of thyrotropin and decreased values of thyroid hormone are hypothyroxinemia. As shown by our observations, it is a relatively frequent situation in the parallel determinations of TSH and free thyroxine, when results verging on hyperthyroxinemia were found in 7% of cases (6.74%, n=259,590), and also in the parallel sets of TSH and total triiodothyronine when hypotriiodothyroninemia reached 8.5% (8.48%, n=73,143). We are assuming that the main cause of hyperthyroxinemia in the free thyroxine and TSH system is the presence of autoantibodies against thyroxine in patients with autoimmune thyroid disease. The reason of hypotriiodothyroninemia in the system of triiodothyronine and TSH is a decreased concentration of thyroid binding globulin in postmenopausal women. Manufacturers of immunoanalytical kits should take into account the potential adverse effects of autoantibodies against thyroid hormones when measuring the results of immunoassay determination of the free fraction of these hormones.

Evaluation of dysthyronemia in endocrinological patients

Dysthyronemia is the state of the thyroid gland in which the concentration of thyrotropin (TSH) in circulation is within the reference range, but the concentrations of free or total fractions of thyroid hormones (TH) are outside the reference range. Normal values of TSH and increased values of TH are referred to as hyperthyroxinemia or hypertriiodothyroninemia, while normal values of TSH and decreased values of TH are called hypothyroxinemia or hypotriiodothyroninemia.

Thyroid diagnostic tests were carried out at the Institute of Endocrinology, Prague, Czech Republic, in 1999–2009 using the immunoanalytical systems of Roche Diagnostics GmbH, Germany (Elecsys 2010, Modular E170).

Hyperthyroxinemia was found in 6.74% of all parallel sets of TSH and free thyroxine (FT4, n=259,590) values. Hypotriiodothyroninemia was observed in 8.48% of all parallel sets of TSH and total triiodothyronine (TT3, n=73,143). The occurrence of hyperthyroxinemia (TSH-FT4) and hypotriiodothyroninemia (TSH-TT3) was >3 times higher than the occurrence of dysthyronemia for the combinations TSH-FT4 (hypothyroxinemia), TSH-TT4 (total thyroxine, n=1996), TSH-FT3 (free triiodothyronine, n=94,090), and TSH-TT3 (hypertrijodthyroninemia), and >5 times higher in comparison with the combinations TSH-FT4-FT3 (n=93,683), TSH-FT4-TT3 (n=72,373), TSH-FT3-TT3 (n=2466), TSH-TT4-TT3 (n=1779), TSH-FT4-TT4 (n=1571), and TSH-FT3-TT4 (n=1466).

In light of our patient types, we are assuming that the observed hypotriiodothyroninemia (TSH-TT3, 8.48%) is due to a decreased concentration of thyroid binding globulin in postmenopausal women and that hyperthyroxinemia (TSH-FT4, 6.74%) is caused mainly by endogenous autoantibodies against thyroxine in patients with thyroid autoimmune diseases.

IN VITROEFFECTS OF EPRISTERIDE ON SPERM IN RATS, DOGS AND MAN

The study was conducted to evaluate in vitro effects of epristeride on sperm in rats, beagle dogs and man. Semen samples were divided into 4 groups and treated with vehicle and epristeride. Motility and motile rate of sperm were videotaped and analyzed with CASA system after 1 h and 2 h incubation periods. Percentage of motile sperm (MOT) of rat sperm decreased after the treatment with epristeride (final concentrations were 0.6, 6 and 60 micromol/L) for 1 h, and MOT of rat sperm treated with middle dose and high dose levels of epristeride also decreased after 2 h, while MOT of dog sperm that treated with three dose levels of epristeride decreased after 2 h. Amplitude of lateral head displacement (ALH) and MOT of human sperm decreased after 2 h with 4.8 micromol/L epristeride treatment. Curvilinear velocity (VCL) and straight-line velocity (VSL) of rat sperm and human sperm changed after 2 h, but there were no significant differences. Therefore, epristeride had a toxic effect on sperm, and the effect varied in different species.

Interferences in hormone immunoassays

Despite the numerous potential interferences that were discussed in this article, immunoassays, in general, are robust measurement systems. There is no practical way to identify specimens a priori that are likely to have immunoassay interference. Therefore, laboratories must rely on communication from clinicians to identify suspicious test values that may be caused by assay interference. After laboratories are alerted, multiple investigations can be undertaken. The common causes of immunoassay interferences (see Box I) are dependent on the analytic format. Competitive assays are most likely to have problems with cross-reactivity, whereas immunometric assays most often have problems with heterophile antibodies. The simple steps to test for dilutional linearity, spiked recovery, heterophile antibody blocking,and testing with alternate technology can help in the evaluations of cases that are suspected to have assay interference.

Transient elevation of triiodothyronine caused by triiodothyronine autoantibody associated with acute Epstein-Barr-virus infection

A unique 16-year old female patient presented after acute Epstein-Barr virus (EBV) infection with severe primary hypothyroidism. Her thyroid test results were thyrotropin level (TSH) of 198 mU/L (normal, 0.4-4 mU/L), free thyroxine [FT(4)], 2.5 pmol/L (normal, 10-25 pmol/L), total triiodothyronine (TT(3)) > 19.5 nmol/L (normal, 1.3-2.7 nmol/L), and free triiodothyronine (FT(3)), 0.77 pmol/L (normal, 3.3-6.3 pmol/L). She had high titers of thyroglobulin and thyroid peroxidase autoantibodies. In vitro triiodothyronine (T(3))-binding measured by radioimmunoprecipitation was 86% (normal, up to 8.5%) and thyroxine (T(4))-binding 8.2% (normal, 6.4%). Serum immunoglobulin G (IgG) absorption, achieved by protein-G Sepharose beads, decreased TT(3) toward normal. Levothyroxine treatment normalized the low baseline FT(4) and FT(3) values, and suppressed TSH to normal. However, TT(3) remained highly elevated and returned to normal after 20 months, while T(3 )binding gradually decreased. Thus, her severe hypothyroidism was masked by this unusual phenomenon. Thirty-four patients with EBV infection (15 with acute disease and 19 with previous infection) were tested for thyroid hormone levels. EBV antibodies (early antigen immunoglobulin M [IgM] and IgG and anti-Epstein-Barr virus nuclear antigen [EBNA] IgG) were measured by enzyme-linked immunosorbent assay (ELISA). In 15 patients with acute EBV the mean TT(3) level was 2.47 +/- 0.39 nmol/L (5 had TT(3) values above normal) compared to a mean TT(3) of 1.70 +/- 0.53 nmol/L in 19 subjects with previous infection (p < 0.0005; only 1 had a TT(3) result above normal), with no differences in FT(4) and TSH concentrations between the two groups. Acute EBV infection may be associated with transient mild to severe TT(3) elevation as a result of assay interference by anti-T(3) autoantibodies.

Antibody interference in thyroid assays: a potential for clinical misinformation

Measurements of thyrotropin and of total and free thyroxine and triiodothyronine are widely used diagnostic methods for thyroid function evaluation. However, some serum samples will demonstrate a nonspecific binding with assay reagents that can interfere with the measurement of these hormones. Several recent case reports have described the presence of such interferences resulting in reported abnormal concentrations of thyroid hormones inconsistent with the patient’s thyroid state. Circulating thyroid hormone autoantibodies, described in thyroid and nonthyroid disorders, are an important class of interference factor and can bind to hormone tracers used in various immunoassays. Two additional categories of interfering antibodies may particularly interfere within two-site immunoassays for thyrotropin. These include heterophile antibodies, especially human anti-mouse antibodies, and rheumatoid factors, which can cause interferences by immunoglobulin aggregation and (or) cross-linking of both capture and signal antibodies. Here we review the nature of these disturbances; their occurrence, prevalence, and detection; and the clinical consequences of the failure to recognize such interference.

Changes in mitochondrial activity during avian myoblast differentiation: influence of triiodothyronine or v-erb A expression

Numerous data suggest that mitochondrial activity is involved in the regulation of cell growth and differentiation. Therefore, we have studied the changes in mitochondrial activity in avian myoblast cultures (QM7 line) undergoing differentiation or in BrdU-treated, differentiation-deficient cells. As we have previously shown that triiodothyronine and v-erb A expression stimulate myogenic differentiation, we have also observed their influence upon mitochondrial activity. Comparison of control and BrdU-treated myoblasts indicated that precocious differentiation events were associated with a stimulation of citrate synthase and cytochrome oxidase activities. They also induced a transient decrease in mitochondrial membrane potential assessed by rhodamine 123 uptake. In control myoblasts, a general stimulation of mitochondrial activity was recorded at cell confluence, prior to terminal differentiation. These events did not occur in BrdU-treated myoblasts, thus indicating that they were tightly linked to myoblast commitment. Whereas no significant triiodothyronine influence could be detected upon mitochondrial activity, we observed that v-erb A expression significantly depresses the mitochondrial membrane potential in control myoblasts. This action was not observed in BrdU-treated myoblasts, thus suggesting that it involves an indirect pathway linked to differentiation. Moreover, the oncoprotein abrogated the decrease in E2-PDH subunit level observed at cell confluence. These data underline that changes in mitochondrial activity occurred prior to myoblast terminal differentiation and could be involved in the processes regulating myogenesis. In addition, they provide the first evidence that the v-erb A oncoprotein influences mitochondrial activity.

Hypothyroidism in association with systemic amyloidosis

BACKGROUND

Systemic amyloidosis leads to functional compromise of various organs through infiltration of these tissues by amyloid protein. The majority of affected patients develop infiltration of the thyroid gland; yet thyroid dysfunction rarely occurs.

METHODS AND RESULTS

Described herein is a case of hypothyroidism occurring in a patient with amyloid goiter. An alternative explanation for her hypothyroidism could not be determined by histologic or serologic evaluation. Hormonal assays were consistent with progressive hypothyroidism in spite of oral and, finally, parenteral replacement therapy. A review of the literature describes other cases of thyroid dysfunction reported in patients with systemic amyloidosis.

CONCLUSIONS

This case illustrates how amyloid infiltration may be a cause of hypothyroidism in patients with systemic amyloidosis. Therefore, all patients who develop a goiter, including those with systemic amyloidosis, must be screened for thyroid dysfunction. When a physician diagnoses the patient with hypothyroidism, that physician must be aware of potential pitfalls in the administration of thyroxine replacement as outlined below.