Anti-thyroid peroxidase antibodies in thyroid disorders and non-thyroid autoimmune diseases

An update on thyroid disorders in the postpartum period

PURPOSE

To review the pathophysiology, diagnosis and management of postpartum thyroid dysfunction, and related management of thyroid disorders during lactation.

METHODS

We reviewed the literature on postpartum thyroid dysfunction and management of thyroid disorders during lactation.

RESULTS

The postpartum period is characterized by a rebound from the immunotolerance induced by pregnancy. Routine thyroid function screening is not recommended for asymptomatic women in the postpartum period. Testing thyroid function should be considered at 6-12-week postpartum for high-risk populations, including women with a previous episode of postpartum thyroiditis, Graves' disease, or those with Hashimoto's thyroiditis on thyroid hormone replacement, known thyroid peroxidase antibody positivity, type 1 diabetes mellitus, other nonthyroidal autoimmune disease, or chronic hepatitis C. A serum TSH should also be checked in the setting of postpartum depression or difficulty lactating. If patients have thyrotoxicosis, new-onset or recurrent Graves' disease must be differentiated from postpartum thyroiditis, because the management differs. Periodic thyroid function testing is recommended following recovery from postpartum thyroiditis due to high lifetime risk of developing permanent hypothyroidism. Levothyroxine, and the lowest effective dose of antithyroid drugs, (propylthiouracil, methimazole, and carbimazole) can be safely used in lactating women. The use of radiopharmaceutical scanning is avoided during lactation and radioactive iodine treatment is contraindicated.

CONCLUSIONS

Diagnosing postpartum thyroid dysfunction is challenging, because symptoms may be subtle. A team approach involving primary care providers, endocrinologists, and obstetricians is essential for transitioning thyroid care from the gestational to the postpartum setting.

Association of Thyroid Peroxidase Antibodies and Thyroglobulin Antibodies with Thyroid Function in Pregnancy: An Individual Participant Data Meta-Analysis

Objectives: Thyroid autoimmunity is common in pregnant women and associated with thyroid dysfunction and adverse obstetric outcomes. Most studies focus on thyroid peroxidase antibodies (TPOAbs) assessed by a negative-positive dichotomy and rarely take into account thyroglobulin antibodies (TgAbs). This study aimed at determining the association of TPOAbs and TgAbs, respectively, and interdependently, with maternal thyroid function. Methods: This was a meta-analysis of individual participant cross-sectional data from 20 cohorts in the Consortium on Thyroid and Pregnancy. Women with multiple pregnancy, pregnancy by assisted reproductive technology, history of thyroid disease, or use of thyroid interfering medication were excluded. Associations of (log2) TPOAbs and TgAbs (with/without mutual adjustment) with cohort-specific z-scores of (log2) thyrotropin (TSH), free triiodothyronine (fT3), total triiodothyronine (TT3), free thyroxine (fT4), total thyroxine (TT4), or triiodothyronine:thyroxine (T3:T4) ratio were evaluated in a linear mixed model. Results: In total, 51,138 women participated (51,094 had TPOAb-data and 27,874 had TgAb-data). Isolated TPOAb positivity was present in 4.1% [95% confidence interval, CI: 3.0 to 5.2], isolated TgAb positivity in 4.8% [CI: 2.9 to 6.6], and positivity for both antibodies in 4.7% [CI: 3.1 to 6.3]. Compared with antibody-negative women, TSH was higher in women with isolated TPOAb positivity (z-score increment 0.40, CI: 0.16 to 0.64) and TgAb positivity (0.21, CI: 0.10 to 0.32), but highest in those positive for both antibodies (0.54, CI: 0.36 to 0.71). There was a dose-response effect of higher TPOAb and TgAb concentrations with higher TSH (TSH z-score increment for TPOAbs 0.12, CI: 0.09 to 0.15, TgAbs 0.08, CI: 0.02 to 0.15). When adjusting analyses for the other antibody, only the association of TPOAbs remained statistically significant. A higher TPOAb concentration was associated with lower fT4 (p < 0.001) and higher T3:T4 ratio (0.09, CI: 0.03 to 0.14), however, the association with fT4 was not significant when adjusting for TgAbs (p = 0.16). Conclusions: This individual participant data meta-analysis demonstrated an increase in TSH with isolated TPOAb positivity and TgAb positivity, respectively, which was amplified for individuals positive for both antibodies. There was a dose-dependent association of TPOAbs, but not TgAbs, with TSH when adjusting for the other antibody. This supports current practice of using TPOAbs in initial laboratory testing of pregnant women suspected of autoimmune thyroid disease. However, studies on the differences between TPOAb- and TgAb-positive women are needed to fully understand the spectrum of phenotypes.

Recent advances in understanding autoimmune thyroid disease: the tallest tree in the forest of polyautoimmunity

Autoimmune thyroid disease (AITD) is often observed together with other autoimmune diseases. The coexistence of two or more autoimmune diseases in the same patient is referred to as polyautoimmunity, and AITD is the autoimmune disease most frequently involved. The occurrence of polyautoimmunity has led to the hypothesis that the affected patients suffer from a generalized dysregulation of their immune system. The present review summarizes recent discoveries unravelling the immunological mechanisms involved in autoimmunity, ranging from natural autoimmunity to disease-specific autoimmunity. Furthermore, the clinical grounds for considering AITD in a setting of polyautoimmunity are explored. A better understanding of these may pave the way for designing new treatment modalities targeting the underlying immune dysregulation when AITD appears in the context of polyautoimmunity.

Definition of the upper reference limit for thyroglobulin antibodies according to the National Academy of Clinical Biochemistry guidelines: comparison of eleven different automated methods

Purpose

In the last two decades, thyroglobulin autoantibodies (TgAb) measurement has progressively switched from marker of thyroid autoimmunity to test associated with thyroglobulin (Tg) to verify the presence or absence of TgAb interference in the follow-up of patients with differentiated thyroid cancer. Of note, TgAb measurement is cumbersome: despite standardization against the International Reference Preparation MRC 65/93, several studies demonstrated high inter-method variability and wide variation in limits of detection and in reference intervals. Taking into account the above considerations, the main aim of the present study was the determination of TgAb upper reference limit (URL), according to the National Academy of Clinical Biochemistry guidelines, through the comparison of eleven commercial automated immunoassay platforms.

Methods

The sera of 120 healthy males, selected from a population survey in the province of Verona, Italy, were tested for TgAb concentration using eleven IMA applied on as many automated analyzers: AIA-2000 (AIA) and AIA-CL2400 (CL2), Tosoh Bioscience; Architect (ARC), Abbott Diagnostics; Advia Centaur XP (CEN) and Immulite 2000 XPi (IMM), Siemens Healthineers; Cobas 6000 (COB), Roche Diagnostics; Kryptor (KRY), Thermo Fisher Scientific BRAHMS, Liaison XL (LIA), Diasorin; Lumipulse G (LUM), Fujirebio; Maglumi 2000 Plus (MAG), Snibe and Phadia 250 (PHA), Phadia AB, Thermo Fisher Scientific. All assays were performed according to manufacturers’ instructions in six different laboratories in Friuli-Venezia Giulia and Veneto regions of Italy [Lab 1 (AIA), Lab 2 (CL2), Lab 3 (ARC, COB and LUM), Lab 4 (CEN, IMM, KRY and MAG), Lab 5 (LIA) and Lab 6 (PHA)]. Since TgAb values were not normally distributed, the experimental URL (e-URL) was established at 97.5 percentile according to the non-parametric method.

Results

TgAb e-URLs showed a significant inter-method variability. Considering the same method, e-URL was much lower than that suggested by manufacturers (m-URL), except for ARC and MAG. Correlation and linear regression were unsatisfactory. Consequently, the agreement between methods was poor, with significant bias in Bland–Altman plot.

Conclusions

Despite the efforts for harmonization, TgAb methods cannot be used interchangeably. Therefore, additional effort is required to improve analytical performance taking into consideration approved protocols and guidelines. Moreover, TgAb URL should be used with caution in the management of differentiated thyroid carcinoma patients since the presence and/or the degree of TgAb interference in Tg measurement has not yet been well defined.

Sex- and Age-Specific Reference Values and Cutoff Points for TPOAb: Tehran Thyroid Study

BACKGROUND

Current guidelines used for establishing reference intervals for thyroid peroxidase antibodies (TPOAb), recommended by the National Academy of Clinical Biochemistry, have been a matter of controversy. The present study sought to determine TPOAb reference intervals for different age and sex groups, as well as the TPOAb cutoff points for subclinical and overt hypothyroidism in an iodine-sufficient population.

METHODS

This cross-sectional study was conducted within the framework of the prospective Tehran Thyroid Study (TTS), in which 4174 healthy euthyroid individuals were followed for 10 years. Thyroid function tests and TPOAb were assessed.

RESULTS

The mean age ± standard deviation of participants was 39.3 ± 15.2 years. Estimated reference intervals for TPOAb corresponding to the 2.5th and 97.5th percentiles were 1.5-32.8 and 2.1-35 IU/mL in males and females, respectively. There were no significant variations in the different age groups in either sex. The optimal cutoff points for TPOAb were 18.38 and 14.77 IU/mL for predicting clinical and subclinical hypothyroidism, respectively.

CONCLUSIONS

This study establishes the reference intervals and the optimal cutoff points for TPOAb in an iodine-sufficient population.

Antithyroid peroxidase antibody positivity is associated with lower incidence of metastasis in breast cancer

Thyroid extracts were first used to treat patients with metastatic breast cancer over a century ago. Since then, a number of studies have investigated the association between thyroid disorders and breast cancer. The presence of antibodies to thyroid peroxidase (TPOab) was recently reported to be associated with improved outcome in these patients. The aim of the present study was to evaluate the association between TPOab positivity and clinicopathological characteristics in breast cancer patients. The study included 318 newly diagnosed cases of breast cancer treated at Ondokuz Mayis University Hospital, Samsun, Turkey, between 2008 and 2012. Serum thyroid-stimulating hormone, free triiodothyronine and free thyroxine levels were measured at the time of diagnosis. Of the 318 patients, 253 were considered to be TPOab-negative (TPOab ≤34 IU/ml) and 65 TPOab-positive (TPOab >34 IU/ml). No cases with distant metastases were found in the TPOab-positive group. However, 20 (7.9%) of the 253 patients displayed distant metastases in the TPOab-negative group (P=0.01). Therefore, TPOab positivity was found to be associated with a lower incidence of metastasis in breast cancer patients.

Comparative study of ultrasound and computed tomography for incidentally detecting diffuse thyroid disease

The aim of this study was to compare the diagnostic values of thyroid ultrasound (US) and neck computed tomography (CT) in incidentally detecting diffuse thyroid disease (DTD). A single radiologist made US and CT diagnoses of incidentally detected DTD in 130 consecutive patients before thyroidectomy for various malignancies. Histopathologic examinations confirmed normal thyroid (n = 80), Hashimoto thyroiditis (n = 20), non-Hashimoto lymphocytic thyroiditis (n = 28) and diffuse hyperplasia (n = 2). Receiver operating characteristic curves revealed that the best diagnostic indices of both imaging methods were achieved on the basis of two or more abnormal imaging findings. The sensitivity, specificity and accuracy of US and CT in incidentally detecting DTD by this classification were 72% and 72%, 87.5% and 91.3% and 81.5% and 83.8%, respectively. Thyroid US and neck CT have similar diagnostic values for differentiating incidental DTD from normal thyroid.

Methods for the investigation of thyroid function

In the developed world, all routine clinical laboratories should be able to perform tests for the assessment of the pituitary-thyroid axis. Testing strategies usually involve the measurement of thyroid-stimulating hormone (TSH), either alone or in combination with free thyroxine (FT4), which itself should also be measured when TSH is abnormal or if there is a suspicion of pituitary disease. Based on these findings, clinical history and medications such as amiodarone, free tri-iodothyronine (FT3), thyroid-binding globulin (TBG), and/or autoantibodies may then be measured. All these assays have their individual challenges. For example, sensitivity of a TSH assay is of crucial importance for improving distinction between eu- and hyperthyroidism. In the measurement of free hormones, there is the potential disturbance of the equilibrium between free and bound moieties by separating systems. There are a number of commercial diagnostic kits available for each of these tests. This chapter presents various representative assays and their principles. With the exception of FT4 determination by equilibrium dialysis, those that employ a 96-well plate format and use non-isotopic techniques have been described. Attention has been paid to limitations of the assays, standardization of assay kits, imprecision, recovery, detection limit, and ease of use. The assays described have been given as typical and reliable examples, but it is the responsibility of assayists to choose methods that are best suited to their needs.

Computed tomography features of incidentally detected diffuse thyroid disease

Objective. This study aimed to evaluate the CT features of incidentally detected DTD in the patients who underwent thyroidectomy and to assess the diagnostic accuracy of CT diagnosis. Methods. We enrolled 209 consecutive patients who received preoperative neck CT and subsequent thyroid surgery. Neck CT in each case was retrospectively investigated by a single radiologist. We evaluated the diagnostic accuracy of individual CT features and the cut-off CT criteria for detecting DTD by comparing the CT features with histopathological results. Results. Histopathological examination of the 209 cases revealed normal thyroid (n = 157), Hashimoto thyroiditis (n = 17), non-Hashimoto lymphocytic thyroiditis (n = 34), and diffuse hyperplasia (n = 1). The CT features suggestive of DTD included low attenuation, inhomogeneous attenuation, increased glandular size, lobulated margin, and inhomogeneous enhancement. ROC curve analysis revealed that CT diagnosis of DTD based on the CT classification of "3 or more" abnormal CT features was superior. When the "3 or more" CT classification was selected, the sensitivity, specificity, positive and negative predictive values, and accuracy of CT diagnosis for DTD were 55.8%, 95.5%, 80.6%, 86.7%, and 85.6%, respectively. Conclusion. Neck CT may be helpful for the detection of incidental DTD.

Diagnostic value of antithyroid peroxidase antibody for incidental autoimmune thyroiditis based on histopathologic results

Detection of antithyroid peroxidase antibody (TPOAb) is widely used in the diagnosis of autoimmune thyroiditis (AIT), but no research has evaluated the diagnostic accuracy of TPOAb detection using histopathologic reference standards. To fill this research gap, this study assessed the diagnostic accuracy of detection of TPOAb and that of other serological markers in asymptomatic patients who had been diagnosed with AIT by histopathologic analysis after thyroid surgery. After review of patient records, 598 patients who had undergone thyroid nodule surgery were enrolled for examination for thyroid parenchyma by a pathologist and classification into no co-existing lymphocytic thyroiditis, Hashimoto thyroiditis, or non-Hashimoto type of lymphocytic thyroiditis (NHLT). The correlation between patient serological data and thyroid parenchyma pathology was analyzed. Statistically significant differences (P < 0.05) were found between co-existing lymphocytic thyroiditis and no co-existing lymphocytic thyroiditis groups regarding thyroid-stimulating hormone (TSH) and TPOAb levels. And, TPOAb titer was significantly associated with the degree of inflammation. An abnormal TPOAb titer was found in 86 of the 598 patients (14.4 %) and the specificity of TPOAb detection for AIT diagnosis was found to be 96.9 %. The prevalence of Hashimoto thyroiditis and NHLT in the 560 papillary thyroid cancer (PTC) patients was found to be 7.9 and 17.9 %, respectively. The results indicate that TPOAb titer is associated with the degree of thyroid inflammation and that detection of TPOAb is a very specific means of diagnosing AIT. The results also indicate that the incidence of AIT and PTC coexistence is relatively high.

A variant of the Il2ra / Cd25 gene predisposing to graves' disease is associated with increased levels of soluble interleukin-2 receptor

Alpha-subunit of the IL-2 receptor (IL-2Rα) encoded by the IL2RA/CD25 gene binds IL-2 that plays a pivotal role in the regulation of T cell function. Levels of a soluble form of IL-2Rα (sIL-2Rα) lacking the transmembrane and cytoplasmic domains were shown to be increased in several autoimmune diseases including Graves' disease (GD). Recent studies showed association between the IL2RA/CD25 gene variants and several autoimmune diseases including GD. In this study, we analyzed whether polymorphic markers rs2104286, rs41295061, and rs11594656 located at the IL2RA/CD25 locus confer susceptibility to GD and are related to increased concentrations of sIL-2Rα. A total of 1474 Russian GD patients and 1609 control subjects were genotyped for rs2104286, rs41295061, and rs11594656 using a Taqman assay. Concentrations of sIL-2Rα in sera of affected and non-affected individuals were measured using an ELISA test. A minor allele A of rs41295061 showed significant association with increased risk of GD [odds ratio (OR) = 1.43, P(c)  = 0.00102]. The allele A of rs41295061 and allele A of rs11594656 constitute a higher risk haplotype AA (OR = 1.47, P(c)  = 0.0477). Compared to carriers of the protective haplogenotype GT/GT, the carriage of two copies of the haplogenotype AA/AA was associated with elevated levels of sIL-2Rα in both GD patients (AA/AA versus GT/GT: 1.35 ± 0.47 ng/ml versus 1.12 ± 0.45 ng/ml, P = 0.0065) and healthy controls (AA/AA versus GT/GT: 0.67 ± 0.28 ng/ml versus 0.51 ± 0.33 ng/ml, P = 0.0098). This is the first report presenting correlation between the carriage of disease-associated variants of IL2RA/CD25 with increased levels of sIL-2Rα in GD.

The -112G>A polymorphism of the secretoglobin 3A2 (SCGB3A2) gene encoding uteroglobin-related protein 1 (UGRP1) increases risk for the development of Graves' disease in subsets of patients with elevated levels of immunoglobulin E

The human secretoglobin 3A2 (SCGB3A2) gene encoding secretory uteroglobin-related protein 1 (UGRP1) resides on the chromosome region 5q31-33 that harbors a susceptibility locus to several autoimmune and inflammatory diseases, including asthma and Graves' disease (GD). Recently, association between the marker rs1368408 (-112G >A), located in the promoter region of the SCGB3A2 gene, and susceptibility to GD was found in Chinese and UK Caucasians. The study aim was to evaluate whether this polymorphism confers GD susceptibility in a large population cohort comprising 1,474 Russian GD patients and 1,619 controls. The marker rs1368408 was studied using a TaqMan allele discrimination assay. Serum levels of UGRP1 and immunoglobulin E (IgE) were assessed using enzyme-linked immunosorbent assay (ELISA) analyses. Association between the allele A of SCGB3A2 and a higher risk of GD (odds ratio [OR] = 1.33, P = 2.9 × 10(-5)) was shown. Both affected and non-affected carriers of the higher risk genotype A/A had significantly decreased levels of serum UGRP1 compared to the subjects homozygous for G/G (93 ± 37 pg/ml vs. 132 ± 45 pg/ml, P = 0.0011 for GD patients; 77 ± 28 pg/ml vs. 119 ± 33 pg/ml, P = 0.0019 for controls). Serum IgE levels were significantly higher in non-affected subjects homozygous for A/A compared to control individuals homozygous for G/G (153 ± 46 IU/ml vs. 122 ± 40 IU/ml, P = 0.0095). Our data suggest that the carriage of the SCGB3A2 -112A/A variant increases the risk for GD in subsets of patients with elevated levels of IgE, a hallmark of allergic asthma. Therefore, the SCGB3A2 -112G >A polymorphism may be considered as a likely marker linking susceptibility to allergy/asthma and GD on chromosome 5q31-33.

[Correlation of sera concentrations of thyroperoxidase autoantibodies measured by two radioimmunoassays]

INTRODUCTION

Thyroid peroxidase-specific autoantibodies (TPO Abs) are mostly measured in patients with autoimmune thyroid diseases. The aim of this study was to compare TPO Ab concentrations measured by two radioimmunoassays.

MATERIAL AND METHODS

Our investigation included 38 patients. Sera concentrations of TPO Abs were measured by using Cis biointernational (France) and Immunotech (Czech Republic) assays.

RESULTS

Concentrations obtained by two assays were extensively different. The values measured by Cis biointernational assay were higher than ones obtained by Immunotech assay. The statistical arrangement of results showed the direct correlation between the two assays, with the coefficient of agreement R = 0.6239 (p < 0.001). The analysis of relative values (ratio of measured and upper limit values given by the manufacturer) demonstrated the statistically significant difference (p = 0.003) between values measured by Cis biointernational (18.94 +/- 37.22) and by Immunotech assay (4.22 +/- 8.22) concerning the distinction between normal and raised concentrations of TPO Abs. The agreement of results (enhanced or normal TPO Ab concentrations in both tests) was shown in 30 sera samples (78.95%), but in residual 8 sera (21.05%) normal TPO Ab concentrations were obtained by Immunotech, and enchanced by Cis biointernational assay. There is no difference in capability of distinction between normal and pathological results between the two tests (chi12 = 3.484, p > 0.05). The highest concentration of TPO Ab measured by Cis biointernational assay was not the highest one in Immunotech assay, which might be a reflection of different specificity of antibodies used in two diagnostic tests.

CONCLUSION

TPO Ab concentrations obtained by Cis biointernational and Immunotech assays are very different. In several sera samples, normal concentrations of TPO autoantibodies were obtained by Immunotech assay and enhanced by Cis biointernational assay. The highest value obtained by one is not the highest value measured by another assay we used.

Can bone loss be reversed by antithyroid drug therapy in premenopausal women with Graves' disease?

Context

Hyperthyroidism can lead to reduced bone mineral density (BMD) and increased fracture risk particularly in postmenopausal women, but the mechanism behind is still unclear.

Objective

Prospective examination of the influence of thyroid hormones and/or thyroid autoantibodies on BMD in premenopause.

Design

We have examined 32 premenopausal women with untreated active Graves' disease from time of diagnosis, during 18 months of antithyroid drug therapy (ATD) and additionally 18 months after discontinuing ATD. Variables of thyroid metabolism, calcium homeostasis and body composition were measured every 3 months. BMD of lumbar spine and femoral neck were measured at baseline, 18 ± 3 and 36 ± 3 months. Data were compared to base line, a sex- and age matched control group and a group of patients with Hashimoto's thyroiditis treated with non-suppressive doses of levothyroxine.

Results

The study showed significantly (p < 0.002) lower BMD in the thyrotoxic state compared to the control group with subsequent significant improvement during 18 ± 3 months of ATD compared to baseline (p < 0.001). However, during the following 18 months after stopping ATD femoral neck BMD decreased again unrelated to age (more than 0.4% per year, p < 0,002). The wellestablished effect of thyrotoxicosis on calcium homeostasis was confirmed. The positive predictor for best BMD was TSH receptor antibodies (TRAb) while free T4 correlated negatively in the thyrotoxic female Graves' patients (p < 0.02 and p < 0.003). In healthy controls and patients with treated Graves' disease both TSH and T4 correlated negatively to the bone mass (BMC) (p < 0.003).

Conclusion

The results indicated a clinically relevant impact of thyroid function on bone modulation also in premenopausal women with Graves' disease, and further indicated the possibility for a direct action of TRAb on bones.

Thyroid peroxidase and thyroglobulin auto-antibodies in patients with newly diagnosed overt hypothyroidism

OBJECTIVES

Thyroid autoimmunity is a major cause for hypothyroidism. We describe thyroid auto-antibodies in patients with various nosological subtypes of hypothyroidism identified in a population study.

DESIGN

Population-based follow-up study identifying all new cases of hypothyroidism in an open cohort.

METHODS

We established a monitoring system, and identified all new cases with primary overt hypothyroidism (n = 685) in a 4 year period in a well-defined population cohort (2,027,208 person-years of observation). Patients were sub-classified into: spontaneous hypothyroidism, presumably of autoimmune origin (n = 578); non-spontaneous hypothyroidism (associated with medication, delivery, neck-irradiation or subacute thyroiditis, n = 97); and congenital hypothyroidism (n = 10). A total of 186 adult patients (61% of those invited) underwent thyroid ultrasonography and measurements of antibodies against thyroid peroxidase (TPOAb) and thyroglobulin (TgAb).

RESULTS

In spontaneously hypothyroid patients: >99% were antibody-positive (TPOAb or TgAb), TPOAb were more often measurable than TgAb (95.9 vs. 80.7%, p < 0.001). A statistically significant but modest correlation was observed between the two antibodies (Pearson's r2 = 0.11, p < 0.001). In a multivariate regression model both TPOAb and TgAb were positively associated with thyroid enlargement (p < 0.001), whereas no association was found with sex, age, iodine deficiency level or serum TSH level. We found no differences in patient characteristics between those who mainly developed TPOAb vs. those who preferentially harboured TgAb.

CONCLUSIONS

Autoimmunity played a dominant role in practically all patients classified as spontaneously hypothyroid. Thyroid enlargement was associated with high levels of TPOAb and TgAb. We found no clue to why some spontaneously hypothyroid patients predominantly developed TPOAb whereas others mainly generated TgAb.

Performance characteristics of 5 automated thyroglobulin autoantibody and thyroid peroxidase autoantibody assays

BACKGROUND

Measurement of thyroid peroxidase autoantibodies (TPOAb) is useful in diagnosing patients with autoimmune thyroid disease. Measurement of thyroglobulin autoantibodies (TgAb) is used to detect potential interferences with thyroglobulin immunoassays and in limited situations for the diagnosis of autoimmune thyroid disease.

METHODS

The limit of detection, imprecision, reference interval, method comparison and diagnostic concordance for the ADVIA Centaur, ARCHITECT i2000, AxSYM, Immulite 2000, Modular E170 (TPOAb only), and UniCel DxI 800 (TgAb only) methods were evaluated. The Advantage was used as the comparison method.

RESULTS

Total imprecision ranged from 2.6% to 14.9% for TgAb and 2.1% to 15.8% for TPOAb. Passing-Bablok slopes ranged from 0.51 to 10.4 (TgAb) and 1.05 to 7.12 (TPOAb) with correlation coefficients of 0.48 to 0.82 (TgAb) and 0.66 to 0.78 (TPOAb). Assay cutoffs were adjusted using a common set of reference interval samples. Concordance with the Advantage assay using the new cutoffs was found to be improved and ranged from 68.5% to 84.7% (TgAb) and 77.5% to 84.7% (TPOAb).

CONCLUSIONS

Although all assays generally performed well, assay concordance for a negative or positive result ranged from 54.2 to 84.7%. Quantitative agreement between methods was generally poor and methods could not be used interchangeably. Additional standardization efforts are required to improve inter-method agreement.

Screening of SNPs at 18 positional candidate genes, located within the GD-1 locus on chromosome 14q23-q32, for susceptibility to Graves' disease: a TDT study

Graves' disease (GD) is a complex autoimmune thyroid disorder with a strong genetic component. Genome-wide screens resolved several susceptibility loci that contribute to the development of GD. One of the susceptibility loci (GD-1 locus) was mapped on chromosome 14q31. However, a susceptibility gene located within the GD-1 locus remains undefined. Here we screen eighteen single nucleotide polymorphisms (SNPs), each is situated at a corresponding positional candidate gene, located within the GD-1 susceptibility locus on chromosome 14q23-q32, for predisposition to GD using the transmission disequilibrium test in 126 simplex Russian families affected with GD. Among SNPs tested, a significant preferential transmission of the Ala allele (41 transmissions vs. 17 nontransmissions, corrected P=0.031) of the Thr92Ala SNP within the DIO2 gene, encoding type II iodothyronine deiodinase, from parents to affected children was found in a Russian family data set. The Thr92Ala SNP of the DIO2 gene and the D727E substitution of the thyrotropin receptor (TSHR) gene have been found to be in pair-wise linkage disequilibrium. The A92/E727 haplotype showed significant preferential transmission from parents to affected sibling (17 transmissions vs. 8 nontransmissions, P=0.039) in simplex families. This suggests that the Thr92Ala variant of the DIO2 gene is associated or may be in linkage disequilibrium with a functional DIO2 polymorphism which involves in the development of GD in a Russian population.

The insulin-like growth axis in patients with autoimmune thyrotoxicosis: effect of antithyroid drug treatment

OBJECTIVE

Hyperthyroidism is associated with altered growth hormone (GH) secretion. Many patients with thyroid dysfunction experience several poorly described complications such as symptoms and signs also seen in patients with growth hormone deficiency (GHD). We have therefore prospectively evaluated a possible relationship between the thyroid function, body composition, leptin levels and insulin-like growth factor (IGF) related peptides in patients with Graves' disease. DESIGN, PATIENTS, AND MEASUREMENTS: In a prospective group of 24 fasting female patients with Graves' disease (mean age (CI 95%): 40 years (33-47)), we measured serum thyroxine, triiodothyronine, thyrotropine (TSH), TSH receptor antibodies, anti-thyroid peroxidase, leptin, body composition, body mass index (BMI) and IGF-related peptides at diagnosis and after 12 months of treatment with thiamazol (ATD).

RESULTS

In thyrotoxic patients IGF-I plus IGF-II correlated positively with IGFBP-3 at baseline (r = 0.90, p < 0.1 x 10(16)) and after 12 months follow-up (r = 0.87, p < 0.1 x 10(-16)). In the thyrotoxic state total IGF-I, IGF-II, IGF binding protein 3 (IGFBP-3) and acid-labile subunit (ALS) but not free IGF-I decreased significantly from 223 microg/L (189-260) (mean (CI 95%), 877 microg/L (801-953), 4165 microg/L (3772-4577) and 22 mg/L (18-26)) to 198 microg/L (172-226), 788 microg/L (711-865), 3431 microg/L (3135-3741) and 19 mg/L (16-26) (p <0.006), respectively, after 12 months of ATD despite an increase in BMI from 22 (21-23) to 23 kg/m(2) (22-25) (p < 0.0004) but no significant changes in leptin.

CONCLUSIONS

The complex IGF systems seemed intact in thyrotoxic patients but change in body composition and the regulation of leptin and insulin secretion during treatment of autoimmune thyroid disease influence IGF-related peptides leaving the patient in a state somewhat similar to partial GHD, but the mechanism behind these alterations remains unclear.

Increased sensitivity of a new assay for anti-thyroglobulin antibody detection in patients with autoimmune thyroid disease

OBJECTIVES

To verify the cut-off values and to determine the clinical sensitivity of antithyroglobulin (TgAb) determinations using our routine RIA and the new electrochemiluminescent Elecsys assay.

DESIGN AND METHODS

We used the DYNOtest anti-Tgn manual RIA from BRAHMS and the new automated Elecsys electrochemiluminescent immunoassay from Roche Diagnostics. We analyzed 452 sera from the following subjects: 193 euthyroid controls, 163 with treated and untreated autoimmune thyroid diseases (AITD) (108 Graves' disease and 55 thyroiditis), 50 with differentiated thyroid carcinoma, 13 with nonautoimmune thyroid disease and 33 with type 1 diabetes mellitus.

RESULTS

As expected, using the proposed thresholds (BRAHMS 60 kIU/L, Elecsys 115 kIU/L) approximately 6% of the control subjects were positive for TgAb with both methods. In AITD patients, the sensitivity of TgAb determination was significantly higher with the Elecsys assay (51.5%) than with the BRAHMS assay (39.3%). This difference was not observed in the other patient groups.

CONCLUSION

The Elecsys assay can be preferred not only because it is automated and rapid, but also because of its better clinical performance in AITD patients.

Thyroid peroxidase and thyroglobulin autoantibodies in a large survey of populations with mild and moderate iodine deficiency

BACKGROUND AND AIMS

Autoimmune thyroiditis is one of the most common autoimmune disorders. Autoantibodies against the thyroid gland, with thyroid peroxidase antibody (TPO-Ab) and thyroglobulin antibody (Tg-Ab) as the most common autoantibodies, can often be demonstrated in serum in population surveys. In the present study we evaluated if TPO-Ab and Tg-Ab tend to develop in parallel or whether one or the other may be more prevalent in subsets of the population.

METHODS

In a cross-sectional comparative study, performed in two areas of Denmark with mild and moderate iodine deficiency, 4649 randomly selected subjects in age groups between 18 and 65 years were examined. Blood tests were analysed for TPO-Ab and Tg-Ab using assays based on the radioimmunoassay (RIA) technique. The participants answered questionnaires, were clinically examined and had urine samples collected.

RESULTS

The overall prevalence rate of thyroid autoantibodies (TPO-Ab and/or Tg-Ab) was 18.8%. The prevalence rates of TPO-Ab and Tg-Ab were similar (13.1 vs. 13.0%). Both antibodies were more frequent in females than in males, and in females the prevalence rates increased with age. In the age group 60-65 years thyroid antibodies were more frequently measured in sera from moderate than from mild iodine-deficient area (P = 0.02), whereas no differences were seen in younger subjects. In 38.8% of participants with thyroid autoantibodies in serum, both antibodies were present. In sera with both TPO-Ab and Tg-Ab present the concentrations of the antibodies were generally higher than in sera with only one type of antibody present.

CONCLUSION

The prevalence rates of TPO-Ab and Tg-Ab were similar in this large population survey. The results suggest that TPO-Ab and Tg-Ab predominantly develop due to a general alteration in the immune system, whereas specific antigenic mechanisms are probably of less importance. However, further studies are needed to clarify the mechanisms involved in the development of thyroid autoantibodies.

Ultrasound measurement of the horizontal external eye muscles in patients with thyroid disease. Is orbital involvement associated with thyroid autoantibodies?

PURPOSE

To describe ophthalmic findings with emphasis on exophthalmometry and ultrasonic assessment of extraocular eye muscle diameter in a consecutive group of females with Graves' disease (GD), compared with healthy controls and patients with other thyroid diseases. We also investigated the relationship with biochemical markers of thyroid autoimmunity such as TSH receptor antibodies (TRAb) and anti-thyroid peroxidase antibodies (anti-TPO).

METHODS

Seventy adult women (age 26-74 years) with various types of thyroid disease consecutively entered the study at a tertiary referral center for thyroid-associated ophthalmopathy (TAO). Twenty-three had long-standing GD with TAO. Clinically, TAO was mainly absent in 22 with newly diagnosed GD and in seven with relapse of GD. Nine with Hashimoto's thyrolditis and nine with multinodular goiter were included for comparison and 18 healthy females served as controls. A full ophthalmic status included B-scan ultrasonic assessment of the four horizontal rectus muscle thicknesses, and a clinical NOSPECS score was attempted for each.

RESULTS AND CONCLUSIONS

Besides higher NOSPECS scores, the TAO subgroup had higher exophthalmometry and muscle thickness. The GD groups without significant TAO also scored higher in these ratings compared to controls. Hertel recordings, NOSPECS and muscle thicknesses were all correlated in GD but showed no correlation to thyroid antibodies (TRAb and anti-TPO). Thus, the muscle thickness did not correlate with thyroid autoimmune activity. Nevertheless, we found extraocular muscle assessment useful since a) thicker muscles were usually found in patients with GD, with or without evidence of TAO, and b) other space-occupying orbital lesions could be excluded, thereby reducing the need for the more elaborate imaging techniques (CT, MRI, etc.).

Immunoassay of anti-thyroid autoantibodies: high analytical variability in second generation methods

The use of highly sensitive immunometric methods in clinical laboratories to assay anti-thyroid antibodies has progressively expanded in recent years but it is not known whether the new techniques have improved the analytical variability connected with the preceding methodologies. The Italian Society of Laboratory Medicine Study Group on Autoimmune Diseases conducted a collaborative study with the biomedical industry to evaluate the degree of standardization of the new analytical procedures. Twelve companies agreed to participate in the study on the search for anti-thyroglobulin (anti-Tg) and anti-thyroperoxidase (anti-TPO) antibodies in nine sera from patients with autoimmune thyroiditis, and in six sera from patients with non-autoimmune thyroid disease; ten immunometric and three immunofluorescence methods were employed. Agreement of qualitative results was close to 90% for anti-Tg and 97% for anti-TPO, with no important differences between the methods; variability of the quantitative results, expressed as CV% of absolute (in lU/ml) and relative (in cut-off concentration multiples) values was 93.9% and 102.3%, respectively, for anti-Tg, and 75.5% and 62.9%, respectively, for anti-TPO. These findings show that despite the progressive improvement in the analytical techniques, the variability between methods for the assay of anti-Tg and anti-TPO is still unexpectedly high, and probably due to several factors such as uncertainty in defining the positive cutoff concentration, absence of adequate international reference preparations, modality of autoantigen purification, and analytical variability in the assay procedures.

Desenvolvimento e Validação de Um Método Imunofluorométrico Para a Pesquisa de Anticorpos Antiperoxidase Tiroidiana no Soro

Desenvolvemos um ensaio onde TPO altamente purificada, obtida a partir de tecido humano, é adsorvida em poços de placas de microtitulação; após incubação com os soros a serem estudados, a revelação da presença de anticorpos específicos é feita com o emprego de anticorpo monoclonal anti-IgG humana marcado com európio. A sensibilidade do teste é da ordem de 0,6U/mL, e as características de reprodutibilidade bastante aceitáveis. Foram analisadas amostras de soro de 188 indivíduos normais de ambos os sexos (74 com >65 anos), de 54 pacientes com doença de Graves (DG) e de 13 com tiroidite de Hashimoto (TH). O método foi comparado, com base em 97 amostras, com um RIE comercial, encontrando-se alta concordância com índice kappa de 0,959. O estudo do valor de corte para definir a presença de anticorpos anti-TPO em níveis significativos baseou-se na curva ROC, e foi fixado em 10U/mL. A freqüência de anti-TPO positivo na população normal foi de 9,6% em indivíduos até 64 anos e de 16,5% nos com >65 anos; nos pacientes com DG 85,2% apresentaram anti-TPO positivo, sendo 100% nos pacientes com TH. O ensaio descrito mostrou-se sensível e específico e de fácil execução para a detecção de autoanticorpos contra a peroxidase tiroidiana presentes na maioria dos indivíduos com doença auto-imune tiroidiana.

Prevalence of thyroid peroxidase, thyroglobulin and thyrotropin receptor antibodies in a long-term follow-up of juvenile Graves disease

OBJECTIVE

To relate the presence of thyroid peroxidase antibodies (TPO ab), thyroglobulin antibodies (Tg ab) and thyrotropin receptor antibodies (TSH-R ab) to the clinical course in a long-term follow-up of patients with juvenile Graves' disease (JGD).

DESIGN

Patients with JGD were drawn from a Danish retrospective study and reexamined.

RESULTS

A number of 105 patients were reexamined 4-21 years (median 10 years) after diagnosis. Three groups were formed: Gr.1: euthyroid patients with anti-thyroid drug (ATD) cessation more than 12 months before reexamination (n=41). Gr.2: patients still on ATD (n=24). Gr.3: subtotally thyroidectomized patients (n=40). Positive TPO ab titers were found in 75% of the patients. In 13% of the patients the titers were very high: >10,000 U/ml. Positive Tg ab were found in 51%. The prevalence of TPO ab and Tg ab was the lowest in group 3. Stimulating TSH-R ab titers were found in 13%. No patients had blocking TSH-R ab. The prevalence of TSH-R ab was 3% in the euthyroid patients, without surgery performed. 15% in the surgical patients, and 25% in the patients still on ATD.

CONCLUSIONS

Many JGD patients were euthyroid at the long-term follow-up in spite of high TPO ab and Tg ab titers. Stimulating TSH-R ab were rare (13%). According to this presence of TPO ab, Tg ab or TSH-R ab does not predict the final outcome of JGD. Further studies are needed.

Concordance of eight kits for antithyroid peroxidase autoantibodies determination

Numerous methods are proposed to quantify antithyroid peroxidase autoantibodies. No standardization exists but most assays use the standard MRC 66/387 with a calibration factor. Costs of the tests vary between the different kits. We evaluated the concordance of eight peroxidase autoantibodies assay kits in two centres, using a panel of sera from 269 subjects: controls (n=100), patients with autoimmune thyroid disease (n=77; Graves' disease, Hashimoto's thyroiditis), patients with non-autoimmune thyroid disease (n=69; nodular goiter, differentiated thyroid carcinoma) and individual sera with thyroglobulin antibodies only (n=23). The concordance between the eight methods was high, ranging from 88.3% to 98.8% with the total panel of sera. The majority of assays demonstrated high diagnostic performance. We encountered some false-positive results at borderline positive levels, and the nonrecognition of some sera by competitive assays.

The prevalence of thyroid dysfunction in a population with borderline iodine deficiency

OBJECTIVE

We lack information on the influence of borderline iodine deficiency on the occurrence of thyroid dysfunction. Iodine deficiency has been reported to facilitate the development of toxic nodular goitre, whereas a high iodine intake may increase the prevalence of autoimmune hypothyroidism.

SUBJECTS AND METHODS

In a cross-sectional study of a random sample of the general population in our region with borderline iodine deficiency 2656 (65%) of 4073 men and women aged 41 to 71 years participated. Records were made of previous thyroidal illness. Blood samples were drawn for thyroid parameters and TPO Ab values. Iodine and creatinine was assessed in casual urine samples.

RESULTS

Previous or present hyperthyroidism was reported by 1.4% of the participants whereas 0.6% had unknown biochemical hyperthyroidism. All cases of undiagnosed hyperthyroidism were among women. Previously diagnosed and treated hypothyroidism was reported by 1.0% and undiagnosed hypothyroidism was found in 0.4%. Subclinical hyperthyroidism was found in 1.3% and subclinical hypothyroidism in 0.7%. TPO Ab titres >200 kU/l were found in 16.9% of the women and 6.6% of the men, and 83% of participants with TSH >5 mU/l had TPO Ab titres >200 kU/l. Participants with TPO Ab titres between 100 and 200 kU/l had no increased frequency of thyroid dysfunction. The median iodine excretion rate was estimated as 103 microg/day. Serum TSH values were higher in women than in men and showed higher dispersion in women as well as in old age. Serum free T3 was found to be higher in women than in men and increased with age. Serum free T4 showed no sex difference but values increased with increasing age.

CONCLUSION

In our region with borderline iodine deficiency more than 5% of the general population has clinical or subclinical thyroid dysfunction. We found a relatively high prevalence of hyperthyroidism, especially previously undiagnosed disease, but a low prevalence of hypothyroidism as would be expected in an area of iodine deficiency. Hypothyroidism was related to TPO Ab titres of >200 kU/l. Thyroid hormone levels varied with age and sex.

Clinical significance of measurements of antithyroid antibodies in the diagnosis of Hashimoto's thyroiditis: comparison with histological findings

Measurements of antithyroglobulin and antimicrosomal (antiperoxidase) antibodies have been performed widely for the clinical diagnosis of autoimmune thyroid diseases. The present study was designed to compare these antibody titers with histological findings of the thyroid in patients with diffuse goiter who were suspected of having Hashimoto's thyroiditis. One hundred and ten euthyroid or hypothyroid patients (10 males and 100 females; age 48 +/- 15 (SD) years old) with diffuse goiter were studied for the measurement of antithyroglobulin and antimicrosomal or antiperoxidase antibodies by a hemagglutination technique (TGHA and MCHA, respectively) and by a newly developed radioassay (TgAb and TPOAb, respectively). The antibody titers were compared with the histological findings obtained by needle biopsy. TgAb, TPOAb, TGHA, and MCHA were detected in 80 (96.4%), 61 (73.5%), 37 (44.6%), and 54 (65.1%) of 83 patients with histologically proven Hashimoto's thyroiditis, respectively, but in only one (3.7%) of 27 patients without any inflammatory changes in the biopsy specimen. In 55 patients with negative TGHA and MCHA, the TgAb positivity was more closely associated with the histological diagnosis of Hashimoto's thyroiditis than the TPOAb positivity was, the incidence of each antibody in Hashimoto's thyroiditis being 89.7% (26/29) and 27.6% (8/29), respectively. In conclusion, the histological diagnosis of Hashimoto's thyroiditis can most precisely be predicted by the newly developed radioassay for TgAb.

Thyroid function and autoimmunity in pernicious anemia before and during cyanocobalamin treatment

Out of 35 consecutive patients with decreased plasma-cobalamin 22 had newly diagnosed overt pernicious anemia (PA) six of which had a known history of thyroid disease. At referral, 5 of these 6 were thyroid peroxidase antibody (TPOAb)-positive and 2 were thyroglobulin antibody (TgAb)-positive, while none were thyroid stimulating antibody (TSAb)-positive (an overall autoantibody appearance of 83.3%). Fifty percent of the 22 patients had TPOAb and 13.6% had TgAb compared to 18.2% and 4.5%, respectively in sex and age matched healthy controls. Six PA-patients without a history of thyroid disease had thyroid autoantibodies and another patient seroconverted within the first year during treatment with cyanocobalamin. Measurements of serum concentrations of thyroid hormones and thyroid stimulating hormone were performed during the first year of treatment with cyanocobalamin. Two cases of subclinical myxoedema were found among PA-patients and another case was found among patients with latent PA. The female:male ratio of thyroid disease among PA-patients and among thyroid autoantibody-positive PA-patients was interestingly found to be 1:1. Treatment with cyanocobalamin did not have any systematic effect on thyroid function. Routine screening for thyroid function and thyroid autoantibodies in patients with latent or overt PA is recommended.

Prevalence of anti-thyroid peroxidase antibodies in autoimmune and nonautoimmune thyroid disorders in a relatively low-iodine environment

We evaluated the prevalence of antithyroid peroxidase antibodies (anti-TP0 Ab) in 402 patients with thyroid disease and 30 healthy controls by a commercial radioimmunoassay (RIA) and compared the results with the passive hemagglutination (HA) method. The patients in the study had autoimmune thyroid disorders (AITD) such as Graves' disease and Hashimoto's disease or had nonautoimmune thyroid diseases (NAITD) such as thyroid cancer, congenital goiter, endemic goiter, and nodular goiter. Subjects were recruited from a population with a mild iodine deficiency (Sao Paulo, Brazil). The effect of specific therapy (for either thyrotoxicosis or chronic thyroiditis) on the circulating anti-TPO levels was also investigated. Positive anti-TPO Ab was detected in 89.9% of the patients with AITD as compared with a prevalence of positive tests of only 4.8% in patients with NAITD. Positive microsomal antibody (M Ab) was found in 68.4% of the patients with AITD and in 6.4% of the patients with NAITD. A positive and significant correlation was obtained between M Ab and anti-TPO Ab. A positive anti-TPO test with negative anti-M was found in 14.1% of the patients with AITD but in only 4.3% of the patients with NAITD and normal controls. These results suggest that anti-TPO Ab by RIA is more sensitive and specific than M Ab by HA. In patients with AITD, anti-TPO Ab levels usually decreased after treatment, suggesting that this parameter could be used in the follow-up of these thyroid disorders.

Anti-glutamate decarboxylase and other antibodies at the onset of childhood IDDM: a population-based study

Sera obtained at diagnosis from 273 children (0-14 years) with insulin-dependent diabetes mellitus (IDDM) were studied to compare different autoantibody levels. The subjects comprise 75% of all incident cases in New South Wales, Australia, for a 2-year period (ascertainment > 99% complete). Antibodies against glutamate decarboxylase were measured by radioimmunoprecipitation, insulin autoantibodies (on 176 sera collected within 4 days of initiation of insulin therapy) by radioimmunoassay, thyroid peroxidase and antigliadin IgA antibodies by enzyme-linked immunoassay, and anti-endomysial IgA and islet cell antibodies by indirect immunofluorescence. Reference ranges for anti-glutamate decarboxylase and insulin autoantibodies were determined in a group of non-diabetic children. Of the sera 69% were positive for anti-glutamate decarboxylase, 65% for insulin autoantibodies, 71% for islet cell antibodies (> or = 20 Juvenile Diabetes Foundation units), 10% for anti-thyroid peroxidase, 2.6% for antigliadin and 3.0% for anti-endomysial antibodies. Islet cell antibodies and insulin autoantibodies were both negative in 13.7% of the sera, while only 5.8% were negative for all three of islet cell antibodies, insulin autoantibodies and anti-glutamate decarboxylase. There was a higher frequency of anti-glutamate decarboxylase among girls than boys (75% vs 63%, p = 0.03) and a negative correlation between the level of insulin autoantibodies and age at diagnosis (r = -0.41, p < 0.0001). A higher frequency of antithyroid peroxidase was found with increasing age (p = 0.05). Higher titres of islet cell antibodies were associated with a higher frequency of both anti-glutamate decarboxylase (p < 0.0001) and insulin autoantibodies (p = 0.003).(ABSTRACT TRUNCATED AT 250 WORDS)

Thyroid autoantibodies in serum samples with abnormal TSH levels

Serum samples with normal and abnormal levels of thyrotropin (TSH) were tested for thyroid autoantibodies. Thyroid peroxidase (TPO) antibodies were detected by a radioimmunoassay (RIA) and by an agglutination method, and thyroglobulin (Tg) antibodies by an agglutination method. Elevated levels of TPO antibodies were detected in 47% of samples with abnormal and in 12% of samples with normal levels of TSH (p < 0.001). Sixty-one percent of the biochemically hypothyroid and 26% of the biochemically hyperthyroid samples contained these antibodies (p < 0.001). Tg antibodies were only detected together with TPO antibodies. Testing of TPO antibodies from samples with abnormal TSH levels is discussed.

Anti-thyroid peroxidase (anti-TPO) antibodies in thyroid diseases, non-thyroidal illness and controls. Clinical validity of a new commercial method for detection of anti-TPO (thyroid microsomal) autoantibodies

The identification of the thyroid peroxidase (TPO) as the main antigen of the thyroid microsomal fraction has enabled the development of a sensitive and specific assay for detection of the corresponding autoantibodies. We evaluated the diagnostic validity of the anti-TPO assay in 303 patients with different types of thyroid disease and in controls. Clearly elevated anti-TPO values (anti-TPO > 500 units/ml) were found in 59% of patients with thyroiditis but in none of the controls or the patients with non-thyroidal illness. The mean anti-TPO levels in these two control groups were 26 +/- 31 units/ml (mean +/- S.D.) and 39 +/- 34 units/ml, respectively. The highest frequency of positive results (88%) was obtained in patients with auto-immune hypothyroidism (clinical diagnosis: Hashimoto's thyroiditis) followed by patients with Graves' disease (53%). With a cut-off point of 200 units/ml, a sensitivity of 96% was obtained for Hashimoto's thyroiditis and of 59% for Graves' disease with a specificity of 100% (50 cases). The new method (anti-TPO, Dynotest) was compared with three conventional methods (35 samples). The results for all measurements were in general agreement. In two cases the results were clearly discordant: one sample contained high anti-thyroglobulin antibody concentrations, the other was obtained from a patient with non-thyroidal illness. In both instances the 'classical' assays yielded false-positive results. Treatment of autoimmune hyperthyroidism resulted in a median decrease in anti-TPO levels of over 50% after reaching the euthyroid state (P < 0.05), whereas in persistent hyperthyroidism no consistent changes were observed. In autoimmune hypothyroidism a marked variability in anti-TPO levels was noted. Some patients showed a clear decrease in anti-TPO levels during T4 substitution whereas in others no consistent changes were observed.

Expression of recombinant human thyroid peroxidase by the baculovirus system and its use in ELISA screening for diagnosis of autoimmune thyroid disease

The cDNAs coding for human full-length and soluble thyroid peroxidase (TPO) were constructed, cloned into a baculovirus transfer vector and used for infection of Spodoptera frugiperda (Sf9) cells. The soluble TPO lacking 87 amino acids of the C-terminal transmembrane and intracisternal domains was designed as a fusion protein with a histidine-hexapeptide as an affinity ligand at its C-terminus. Whereas the recombinant full-length TPO was expressed mainly in an insoluble form in Sf9 cells, the recombinant soluble TPO was almost completely secreted into the culture medium. Both the full-length and the soluble TPO were purified by conventional methods and by a specific affinity chromatography using metal chelating matrix respectively, and tested for their autoantigenicity towards anti-TPO autoantibodies. The ELISA established with the purified recombinant soluble TPO as antigen demonstrated its specificity, practicability and reproducibility in screening of anti-TPO autoantibodies in sera of autoimmune thyroid patients. High correlation (r = 0.89, n = 175) was obtained between the soluble TPO and natural TPO prepared from human thyroid glands. Pathological sera (n = 200) were positively assayed with a significance of 91%.