Serum thyroglobulin and thyroglobulin autoantibodies in thyroid diseases. Pathogenic and diagnostic aspects

Exploring the Correlation Between Varied Serum Iodine Nutritional Levels and Anti-Thyroglobulin Antibodies

Iodine deficiency results in elevated thyroglobulin (Tg) concentrations, with high iodine Tg being more immunogenic than low iodine Tg. The study investigated the correlation between serum iodine concentration and thyroglobulin autoantibody (TgAb) levels across diverse iodine nutritional statuses as determined by urine iodine concentration (UIC). Demographic information was collected from 1,482 participants through a questionnaire. Blood and spot urine were collected to measure thyroid-stimulating hormone (TSH), TgAb, thyroid anti-peroxidase antibody (TPOAb), serum iodine (SIC), serum non-protein-bound iodine (snPBI), urine iodine (UIC), creatinine (UCr). The median UIC and SIC were 146.5 μg/L and 74.9 μg/L, respectively. A linear relationship was observed between SIC, snPBI, and serum-protein-bound iodine (sPBI) (P < 0.001). The 90% reference intervals for SIC, snPBI, and sPBI were 50.7-120.7 μg/L, 21.9-52.9 μg/L, and 19.7-77.9 μg/L, respectively. The prevalence of elevated TgAb levels was significantly higher in women than in men (P < 0.001). Both low and high levels of snPBI and sPBI were associated with an increased risk of elevated TgAb levels. In women, the risk of positive TgAb in the group below the reference value of snPBI (OR = 2.079, 95%CI: 1.166, 3.705) and sPBI (OR = 2.578, 95%CI: 1.419, 4.684) was higher. In men, the risk of positive TgAb in the group below the reference value of SIC was higher (OR = 3.395, 95%CI: 1.286, 8.962). Iodine might exert an influence on TgAb levels through its binding to proteins, primarily Tg, thereby altering the iodine content of Tg. The interplay of gender factors further enhanced the risk of TgAb emergence.

Genetic analyses in a cohort of Portuguese pediatric patients with congenital hypothyroidism

Background Permanent primary congenital hypothyroidism (CH) can be caused by thyroid dysgenesis or dyshormonogenesis. A molecular genetic study is recommended in dyshormonogenesis, in syndromic hypothyroidism and when there is a family history of CH. The aim of this study was to identify a monogenic etiology for CH in selected individuals from a cohort of primary permanent CH. Methods From an initial cohort of 79 patients with permanent CH (3-19 years), 11 patients were selected for molecular analyses. Nine patients with dyshormonogenesis (normal in-situ gland or goiter) were screened for causative variants, by next-generation sequencing (NGS), in 28 genes known to be responsible for CH. One patient with a family history of CH was screened for the paired-box gene 8 (PAX8) gene and another patient with a syndromic CH was screened for the NKX2-1 gene. Results We found a monogenic basis of disease in eight patients, involving the thyroid peroxidase (TPO) gene (four patients), the thyroglobulin (TG) gene (two patients), and the PAX8 and NKX2-1 genes (one patient each). Two patients were heterozygotes, one harboring a variant in the TG gene and the other in the SLC5A5 gene. In one patient, we found no potential causative variants in any of the 28 genes screened. We described five novel variants: three in the TG gene, one in the NKX2-1 and one in the SLC5A5 gene, all of them classified as pathogenic. Conclusions In eight of the 11 screened patients, a monogenic disease was found. These results highlight the advantage of using an NGS panel and provide further data regarding the molecular basis of CH.

Glycosylation in the Thyroid Gland: Vital Aspects of Glycoprotein Function in Thyrocyte Physiology and Thyroid Disorders

The key proteins responsible for hormone synthesis in the thyroid are glycosylated. Oligosaccharides strongly affect the function of glycosylated proteins. Both thyroid-stimulating hormone (TSH) secreted by the pituitary gland and TSH receptors on the surface of thyrocytes contain N-glycans, which are crucial to their proper activity. Thyroglobulin (Tg), the protein backbone for synthesis of thyroid hormones, is a heavily N-glycosylated protein, containing 20 putative N-glycosylated sites. N-oligosaccharides play a role in Tg transport into the follicular lumen, where thyroid hormones are produced, and into thyrocytes, where hyposialylated Tg is degraded. N-glycans of the cell membrane transporters sodium/iodide symporter and pendrin are necessary for iodide transport. Some changes in glycosylation result in abnormal activity of the thyroid and alteration of the metabolic clearance rate of hormones. Alteration of glycan structures is a pathological process related to the progression of chronic diseases such as thyroid cancers and autoimmunity. Thyroid carcinogenesis is accompanied by changes in sialylation and fucosylation, β1,6-branching of glycans, the content and structure of poly-LacNAc chains, as well as O-GlcNAcylation, while in thyroid autoimmunity the main processes affected are sialylation and fucosylation. The glycobiology of the thyroid gland is an intensively studied field of research, providing new data helpful in understanding the role of the sugar component in thyroid protein biology and disorders.

Serum thyroglobulin (Tg) monitoring of patients with differentiated thyroid cancer using sensitive (second-generation) immunometric assays can be disrupted by false-negative and false-positive serum thyroglobulin autoantibody misclassifications

CONTEXT

Reliable thyroglobulin (Tg) autoantibody (TgAb) detection before Tg testing for differentiated thyroid cancer (DTC) is critical when TgAb status (positive/negative) is used to authenticate sensitive second-generation immunometric assay ((2G)IMA) measurements as free from TgAb interference and when reflexing "TgAb-positive" sera to TgAb-resistant, but less sensitive, Tg methodologies (radioimmunoassay [RIA] or liquid chromatography-tandem mass spectrometry [LC-MS/MS]).

OBJECTIVE

The purpose of this study was to assess how different Kronus (K) vs Roche (R) TgAb method cutoffs for "positivity" influence false-negative vs false-positive serum TgAb misclassifications that may reduce the clinical utility of reflex Tg testing.

METHODS

Serum Tg(2G)IMA, TgRIA, and TgLC-MS/MS measurements for 52 TgAb-positive and 37 TgAb-negative patients with persistent/recurrent DTC were compared. A total of 1426 DTC sera with TgRIA of ≥ 1.0 μg/L had false-negative and false-positive TgAb frequencies determined using low Tg(2G)IMA/TgRIA ratios (<75%) to indicate TgAb interference.

RESULTS

TgAb-negative patients with disease displayed Tg(2G)IMA, TgRIA, and TgLC-MS/MS serum discordances (% coefficient of variation = 24 ± 20%, range, 0%-100%). Of the TgAb-positive patients with disease, 98% had undetectable/lower Tg(2G)IMA vs either TgRIA or TgLC-MS/MS (P < .01), whereas 8 of 52 (15%) had undetectable Tg(2G)IMA + TgLC-MS/MS associated with TgRIA of ≥ 1.0 μg/L. Receiver operating characteristic curve analysis reported more sensitivity for TgAb method K vs R (81.9% vs 69.1%, P < .001), but receiver operating characteristic curve cutoffs (>0.6 kIU/L [K] vs >40 kIU/L [R]) had unacceptably high false-negative frequencies (22%-32%), whereas false positives approximated 12%. Functional sensitivity cutoffs minimized false negatives (13.5% [K] vs 21.3% [R], P < .01) and severe interferences (Tg(2G)IMA, <0.10 μg/L) (0.7% [K] vs 2.4% [R], P < .05) but false positives approximated 23%.

CONCLUSIONS

Reliable detection of interfering TgAbs is method and cutoff dependent. No cutoff eliminated both false-negative and false-positive TgAb misclassifications. Functional sensitivity cutoffs were optimal for minimizing false negatives but have inherent imprecision (20% coefficient of variation) that, exacerbated by TgAb biologic variability during DTC monitoring, could cause TgAb status to fluctuate for patients with low TgAb concentrations, prompting unnecessary Tg method changes and disrupting Tg monitoring. Laboratories using reflexing should limit Tg method changes by considering a patient's Tg + TgAb testing history in addition to current TgAb status before Tg method selection.

How sensitive (second-generation) thyroglobulin measurement is changing paradigms for monitoring patients with differentiated thyroid cancer, in the absence or presence of thyroglobulin autoantibodies

PURPOSE OF REVIEW

To discuss new insights regarding how sensitive (second-generation) thyroglobulin immunometric assays (TgIMAs), (functional sensitivities ≤0.10 μg/L) necessitate different approaches for postoperative thyroglobulin monitoring of patients with differentiated thyroid cancer (DTC), depending on the presence of thyroglobulin autoantibodies (TgAbs).

RECENT FINDINGS

Reliable low-range serum thyroglobulin measurement has both enhanced clinical utility and economic advantages, provided TgAb is absent (∼75% DTC patients). Basal [nonthyroid-stimulating hormone (TSH) stimulated] TgIMA measurement obviates the need for recombinant human TSH stimulation because basal TgIMA below 0.20 μg/L has comparable negative predictive value (>95%) to recombinant human TSH-stimulated thyroglobulin values below the cutoff of 2 μg/L. Now that radioiodine remnant ablation is no longer considered necessary to treat low-risk DTC, the trend and doubling time of low basal thyroglobulin values arising from postsurgical thyroid remnants have recognized prognostic significance. The major limitation of TgIMA testing is interference by TgAb (∼25% DTC patients), causing TgIMA underestimation that can mask disease. When TgAb is present, the trend in TgAb concentrations (measured by the same method) can serve as the primary (surrogate) tumor-marker and be augmented by thyroglobulin measured by a TgAb-resistant class of method (radioimmunoassay or liquid chromatography-tandem mass spectrometry).

SUMMARY

The growing use of TgIMA measurement is changing paradigms for postoperative DTC monitoring. When TgAb is absent, it is optimal to monitor the basal TgIMA trend and doubling time (using the same method) in preference to recombinant human TSH-stimulated thyroglobulin testing. When TgAb is present, interference renders TgIMA testing unreliable and the trend in serum TgAb concentrations per se (same method) can serve as a (surrogate) tumor-marker.

Thyroid autoantibodies in pregnancy: their role, regulation and clinical relevance

Autoantibodies to thyroglobulin and thyroid peroxidase are common in the euthyroid population and are considered secondary responses and indicative of thyroid inflammation. By contrast, autoantibodies to the TSH receptor are unique to patients with Graves' disease and to some patients with Hashimoto's thyroiditis. Both types of thyroid antibodies are useful clinical markers of autoimmune thyroid disease and are profoundly influenced by the immune suppression of pregnancy and the resulting loss of such suppression in the postpartum period. Here, we review these three types of thyroid antibodies and their antigens and how they relate to pregnancy itself, obstetric and neonatal outcomes, and the postpartum.

Evaluating iodine deficiency in pregnant women and young infants—complex physiology with a risk of misinterpretation

Objective:To review methods for evaluating iodine deficiency in pregnant women and young infants and to discuss factors to be considered in the interpretation of their results.

Design:Review of the literature regarding the various methods available for assessing iodine status.

Setting:Population surveys and research studies.

Subjects:Pregnant women and young infants.

Results:Several factors to consider when assessing iodine status in pregnant women and young infants include: 1) the urinary iodine (UI) concentration (μg l-1) is not interchangeable with 24 h UI excretion (μg per 24 h); 2) the concentration of iodine in a spot or casual urine sample cannot be used to diagnose iodine deficiency in an individual; 3) a moderate fall in the concentration of serum free T4 during pregnancy is not a sign of maternal iodine deficiency; 4) an increase in the concentration of serum thyroglobulin (Tg) during pregnancy is not a sign of maternal iodine deficiency; 5) a higher concentration of TSH and Tg in cord blood than in maternal blood is not a sign of iodine deficiency in the mother or neonate; and 6) thyroid function in a full-term foetus, a neonate or a small child is not more sensitive to a mild iodine deficiency than in the mother.

Conclusions:If the iodine status of pregnant women and small children is not to be misjudged, the above six factors need to be taken into account.

Iodine status, thyroid function, thyroid volume and thyroid autoimmunity in patients with type 1 diabetes mellitus in an iodine-replete area

OBJECTIVE

To analyze the prevalence and clinical significance of thyroid autoimmunity, thyroid volume and iodine status in patients with type 1 diabetes mellitus compared with age and sex matched healthy controls, in an iodine-deficiency improved area.

METHOD

Fifty-eight patients with type 1 DM, 30 female and 28 male, who attended the pediatric endocrinology clinic of Karadeniz Technical University Hospital were included into the study. They were compared with 58 healthy children matched for sex and age. Routine thyroid function parameters, thyroid autoantibodies (TPOAb, TGAb and TRAb) and urinary iodine excretion were measured and thyroid volume was determined by ultrasonography (US).

RESULTS

Twenty-six patients (44.8%) in diabetic patients and 20 subjects (34.5%) in the control group had thyroid autoantibody positivity. TPOAb and TGAb positivity were significantly high in diabetic patients (P=0.01 and P=0.032, respectively). Thyroid US revealed a thyroid volume of 6.6+/-3.5 ml (median 6.4 ml, range 1.117.2 ml) in the diabetic patients compared with 3.7+/-2 ml (median 3.1 ml, range 0.8-8.6 ml) in the control group (P=0.0001). Median urinary iodine levels of both groups were clearly above the threshold level for iodine deficiency, but 26 patients with type 1 DM (44.8%) and 16 controls (27.5%) had urinary iodine excretion below 100 microg/L, and 21 (36.2%) of diabetic patients and two subjects (3.4%) of the control group were consistent with severe iodine deficiency. No significant differences were noted in diabetic patients in terms of age, duration and metabolic control of the disease and thyroid volume when compared according to the autoantibody presence. Additionally, there were no significant differences between the iodine deficient and iodine sufficient diabetic patients in terms of age, sex, duration of disease, HbA1c, thyroid hormones and thyroid volumes. Thyroid autoimmunity was lower in patients with iodine deficiency (38.4% vs. 50%), but not statistically significant.

CONCLUSION

We found that type 1 DM patients had larger thyroid volume compared with healthy control groups, and a large portion of them had the markers of autoimmune thyroid disease and iodine deficiency. Surprisingly, we found that a large portion of the healthy children had TRAb positivity. We proposed that TRAb must be considered in community surveys or prevalence studies of autoimmune thyroid disorders in iodine-replete areas. Additionally, prospective longitudinal studies are needed to determine the clinical significance of TRAb positivity in diabetic patients.

Development and validation of an improved enzyme-linked immunosorbent assay for the detection of thyroglobulin autoantibodies in canine serum samples

An enzyme-linked immunosorbent assay to detect thyroglobulin autoantibodies (TGAB) in canine serum was developed and validated. The test result for each sample was derived from the optical density readings (OD) and expressed as an Ab-score(%) calculated from three in-house calibrators. The assay specifically detected TGAB as judged from lack of response in the assay after samples had been incubated with specific antigen. Intra- and interassay coefficients of variation ranged from 2.0-4.9% and 4.6-9.9%, respectively. The detection limit, an Ab-score of 5.6%, was close to the median Ab-score of 10% observed in healthy dogs (n = 132). The median Ab-score of dogs with primary hypothyroidism and lymphocytic thyroiditis (n = 11), skin diseases (n = 35), and non-thyroidal diseases (n = 63) was 340%, 12%, and 8%, respectively. The prevalence of TGAB in hypothyroid dogs with lymphocytic thyroiditis (sensitivity) was 91% (95% confidence limits: 59%-99%). In dogs with dermatological diseases without lymphocytic thyroiditis the prevalence of TGAB was 3% corresponding to a specificity of 97% (95% confidence limit: 85%-100%). In dogs with non-thyroidal diseases and healthy dogs the prevalence of TGAB was 5% and 6%, respectively. The diagnostic accuracy of serum TGAB was evaluated by subjecting the data from 11 dogs with lymphocytic thyroiditis and 35 control dogs without lymphocytic thyroiditis to receiver-operating characteristic curve analysis. The area under the receiver-operating characteristic curve (W = 0.966; 95% confidence limit 87%-100%) was significantly higher than that of a worthless test (0.5) (P < 0.0001), thereby indicating that serum TGAB measurements distinguished between dogs with and without lymphocytic thyroiditis.

Thyroid function in patients with Pendred's syndrome

Thyroid function was studied in 17 unrelated patients with Pendred's syndrome. Fourteen patients had been treated with L-thyroxine, which was withdrawn during the investigation. Eight of the patients had previously had a thyroid resection. Thirteen patients had goiter at the time of study. The serum total thyroxine and serum total triiodothyronine concentrations were normal in 8, of whom 3 had elevated serum TSH concentrations. In the remaining 9 cases the thyroxine levels were below normal with elevated TSH. Serum reverse triiodothyronine concentrations were decreased in 8 out of 11. Median serum thyroglobulin was 973 micrograms/l (range 10.9-3200 micrograms/l) and increased in 13. Three patients had slightly positive thyroglobulin antibodies and one with normal level was thyrodectomized. Thyroid stimulating antibodies as measured by adenylate cyclase stimulation (median 114%, range 85-137%) were slightly increased in 11. When measured as TSH binding inhibiting immunoglobulins none were positive. Thyroid microsomal antibodies were negative in all. All patients with a detectable 131I uptake (n = 15) showed a pathological iodide perchlorate discharge test (median 32%, range 16-46%). These findings indicate an organification defect with impaired hormone synthesis.

Serum thyroglobulin in chronic renal failure--effects of haemodialysis

The influence of chronic renal failure (CRF) on serum thyroglobulin concentration (Tg) was investigated in 37 patients (29 on haemodialysis) and compared with results obtained from matched controls. Serum Tg did not differ significantly between CRF patients not on haemodialysis: median 24.1 micrograms/l, (range 2.5-47.0) and controls: median 23.6 micrograms/l, (range 2.1-53.0). Patients on haemodialysis had a significantly lower serum Tg level: median 11.4 micrograms/l (range 2.1-54.0) compared to controls (p less than 0.01) but no change in serum Tg level could be demonstrated after a single haemodialysis. A possible explanation for the low serum Tg level in patients with CRF on haemodialysis is decreased production parallelling the decreased production rate of T4 and T3. Since CRF patients not on haemodialysis had an unchanged serum Tg level compared to controls, haemodialysis was associated with small changes in serum Tg level, and since none of the patients had a serum Tg value above the upper reference limit we conclude that these changes were not of a magnitude likely to cause misinterpretation of results in routine clinical situations.

Short-term beta-adrenergic blockade decreases serum thyroglobulin in hyper- and euthyroid patients

Cardioselective [Acebutolol (N = 10)] or noncardioselective [Oxprenolol (N = 9)] or [Pindolol (N = 9)] beta-adrenergic blockers were given to patients with suspected hyperthyroidism. Four h after start of the beta blockade median serum thyroglobulin (Tg) had decreased to 33 (range: 13-325) micrograms/l from 41 (range: 12-333) micrograms/l before start in the acebutolol treated group (p less than 0.05). A significant decrease in serum Tg was also found in the oxprenolol-treated group [before start: 45 (24-423) micrograms/l and after 4h: 43 (18-363) micrograms/l (p less than 0.01)] and in the pindolol-treated group [before start: 154 (33-210) micrograms/l and after 4 h: 63 (19-157) micrograms/l (p less than 0.05) treated groups. After 7 days treatment the decrease in serum Tg was significant [to 85 (34-182) micrograms/l (p less than 0.02)] only in the Pindolol-treated group. It is suggested that both hemodynamic changes as well as interference with the intrathyroidal 12 S Tg to 19 S Tg dimerization might explain the changes in serum Tg during beta blockade. Knowledge of drug influence on serum thyroglobulin is important for the interpretation of variations found in patients where thyroglobulin is being used for diagnostic purposes.

Humoral autoimmune manifestation in subacute thyroiditis

To study the autoimmune manifestations in subacute thyroiditis (SAT), the patterns of thyroid antibodies, thyroglobulin and circulating immune complexes were investigated in 10 patients during the course of the disease. Eight patients were thyrotoxic at diagnosis, and became euthyroid during recovery with a median observation of 8 months (4-30 months). Thyroid stimulating immunoglobulins were measured as TSH binding inhibiting immunoglobulins (TBII) and as thyroid stimulating antibodies (TSAb). TBII were present in all patients at least once during the observation period and remained detectable in six patients after recovery. TSAb were detected in three patients without relation to the hyperthyroid state. Thyroglobulin antibodies (TgAb) were present in four patients and persisted in three, while microsomal antibodies (MAb) were negative. Thyroglobulin (Tg) in the TgAb negative patients (n = 6) was high at diagnosis (median 229 micrograms/l, range 55-375) and fell rapidly during the course of SAT. Circulating immune complexes (CIC), which were found in all patients, reached maximal levels shortly after the onset of the disease and persisted after recovery. No correlation could be demonstrated between the different thyroid antibodies, and there was no clear relation between the levels of CIC and presence of the autoantibodies. However, the changes in CIC paralleled the changes in TBII, and it is suggested that immune complex formation is a major feature of the regulatory mechanisms controlling the immune responses in SAT.

An enzyme linked immunosorbent assay (ELISA) for measurement of human serum thyroglobulin. Evaluation of the influence of thyroglobulin auto-antibodies

The aim of the study was to develop an enzyme linked immunosorbent assay (ELISA) for measuring thyroglobulin (Tg) in human serum and to evaluate the influence of serum thyroglobulin auto-antibodies (TgAb) on the ELISA. The sensitivity of the ELISA was 2.1 micrograms/l. Serum Tg levels in healthy controls were from less than 2.1 to 55.5 micrograms/l (n = 46) (95% reference range). With serum Tg concentrations between 19.6 to 90 micrograms/l the within-assay coefficient of variation (CV) was from 4.5 to 6.6% (n = 12) and the between-assay CV from 8.5 to 10.5% (n = 6). The recovery from 20 to 89 micrograms Tg/l serum was from 93 to 101%. There was significant correlation between serum Tg concentrations measured by the ELISA and a RIA method in healthy controls (r = 0.85, n = 46, p less than 0.001) and in patients with differentiated thyroid carcinoma (r = 0.97, n = 28, p less than 0.001). The TgAb interfered with the serum Tg determination both in the ELISA and in the RIA method. The assay is simple and easy to perform, and the equipment is inexpensive and useful for large-scale serum Tg measurements as an alternative to RIA.