European interlaboratory comparison of serum thyroglobulin measurement

Diagnostic, Theranostic and Prognostic Value of Thyroglobulin in Thyroid Cancer

Thyroglobulin (Tg) is an iodinated glycoprotein, which is normally stored in the follicular colloid of the thyroid, being a substrate for thyroid hormone production. Since it is produced by well-differentiated thyroid cells, it is considered a reliable tumor marker for patients with differentiated thyroid carcinoma (DTC) during their follow-up after total thyroidectomy and radioiodine ablation. It is used to monitor residual disease and to detect recurrent disease. After total thyroid ablation, unstimulated highly sensitive Tg measurements are sufficiently accurate to avoid exogenous or endogenous thyrotropin (TSH) stimulation and provide accurate diagnostic and prognostic information in the great majority of DTC patients. Adopting sophisticated statistical analysis, i.e., decision tree models, the use of Tg before radioiodine theranostic administration was demonstrated to be useful in refining conventional, pathology-based risk stratification and providing personalized adjuvant or therapeutic radioiodine administrations. The follow-up of DTC patients aims to promptly identify patients with residual or recurrent disease following primary treatment. Our review paper covers the diagnostic, theranostic and prognostic value of thyroglobulin in DTC patients.

Coexistence of Hashimoto's Thyroiditis in Differentiated Thyroid Cancer: Post-Operative Monitoring of Anti-Thyroglobulin Antibodies and Assessment of Treatment Response

INTRODUCTION

Differentiated thyroid carcinoma (DTC) is frequently found in conjunction with autoimmune thyroid disorders, particularly Hashimoto's thyroiditis (HT). This study investigates the impact of coexisting HT on the persistence of an indeterminate response to therapy due to positive anti-thyroglobulin antibodies (AbTg), measured via competitive immunoassay, in a consecutive patient series from Calabria, Southern Italy.

METHODS

This retrospective longitudinal study analyzed 259 consecutive DTC patients managed at the Endocrinology Unit of Renato Dulbecco Hospital (Catanzaro, Italy) up to 2023. Patients with medullary and undifferentiated thyroid carcinoma, partial thyroidectomy, less than six months of post-operative monitoring, or missing clinical data were excluded. Demographic information, histological findings, initial tumor stage, and ATA risk category were collected. The response to therapy was assessed based on ATA guidelines.

RESULTS

Among the 259 patients, 29% had coexisting HT. Patients with HT exhibited distinct characteristics: a higher proportion of females (87.0% vs. 74.7%), a shorter post-operative monitoring duration (median 3 vs. 5 years), and a higher prevalence of papillary thyroid carcinoma (PTC) (97.4% vs. 86.3%). The tumor size, lymph node involvement, and distant metastasis were similar between the groups, with patients without HT having a higher incidence of extrathyroidal tumor extension. However, the initial TNM stage and ATA risk category did not differ significantly. At the six-month follow-up, HT patients showed a higher rate of indeterminate responses, primarily due to positive AbTg. After 12 months, the response categories aligned, with decreasing AbTg levels in the HT group. After 24 months, most patients with long-term follow-up demonstrated an excellent response to DTC therapy, irrespective of HT coexistence.

CONCLUSIONS

While HT does not worsen DTC prognosis, it may result in indeterminate responses. AbTg measurements in the peri-operative period should be encouraged to facilitate post-operative monitoring, emphasizing the importance of using standardized assays. Further research in larger populations with extended follow-up is needed to comprehensively understand the HT-DTC relationship.

Thyroglobulin and thyroglobulin antibody: an updated clinical and laboratory expert consensus

OBJECTIVE

Thyroglobulin measurement is the cornerstone of modern management of differentiated thyroid cancer, with clinical decisions on treatment and follow-up based on the results of such measurements. However, numerous factors need to be considered regarding measurement with and interpretation of thyroglobulin assay results.

DESIGN

The present document provides an integrated update to the 2013 and 2014 separate clinical position papers of our group on these issues.

METHODS

Issues concerning analytical and clinical aspects of highly-sensitive thyroglobulin measurement will be reviewed and discussed based on an extensive analysis of the available literature.

RESULTS

Thyroglobulin measurement remains a highly complex process with many pitfalls and major sources of interference, especially anti-thyroglobulin antibodies, need to be assessed, considered and, when necessary, dealt with appropriately.

CONCLUSIONS

Our expert consensus group formulated 53 practical, graded recommendations for guidance on highly-sensitive thyroglobulin and TgAb in laboratory and clinical practice, especially valuable where current guidelines do not offer sufficient guidance.

Laboratory Thyroid Tests: A Historical Perspective

Background: This review presents a timeline showing how technical advances made over the last seven decades have impacted the development of laboratory thyroid tests. Summary: Thyroid tests have evolved from time-consuming manual procedures using isotopically labeled iodine as signals (¹³¹I and later ¹²⁵I) performed in nuclear medicine laboratories, to automated nonisotopic tests performed on multianalyte instruments in routine clinical chemistry laboratories. The development of isotopic radioimmunoassay techniques around 1960, followed by the advent of monoclonal antibody technology in the mid-1970s, led to the development of a nonisotopic immunometric assay methodology that forms the backbone of present-day thyroid testing. This review discusses the development of methods for measuring total thyroxine and triiodothyronine, direct and indirect free thyroid hormone measurements and estimates (free thyroxine and free triiodothyronine), thyrotropin (TSH), thyroid autoantibodies (thyroperoxidase, thyroglobulin [Tg] and TSH receptor autoantibodies), and Tg protein. Despite progressive improvements made in sensitivity and specificity, current thyroid tests remain limited by between-method differences in the numeric values they report, as well as nonspecific interferences with test reagents and interferences from analyte autoantibodies. Conclusions: Thyroid disease affects ∼10% of the U.S. population and is mostly managed on an outpatient basis, generating 60% of endocrine laboratory tests. In future, it is hoped that interferences will be eliminated, and the standardization/harmonization of tests will facilitate the establishment of universal test reference ranges.

Prognostic role of FDG PET/CT in patients with differentiated thyroid cancer treated with 131-iodine empiric therapy

BACKGROUND

To assess the long-term prognostic value of F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) in patients with differentiated thyroid carcinoma (DTC) undergoing empiric radioiodine (RAI) therapy due to raising values of thyroglobulin (Tg).

METHODS

Forty-nine patients with histological diagnosis of DTC (31 with papillary and 18 with follicular carcinoma) follow-up for a mean period of 7.9 ± 5 years after empiric RAI therapy were retrospectively analyzed.

RESULTS

FDG-PET/CT was negative in 15 (30.6%) patients and positive in 34 (69.4%), whereas postradioiodine therapy whole body scan (t-WBS) was negative in 16 (32.7%) and positive in 33 (67.3%) patients. FDG-PET/CT and t-WBS were in agreement in 32 patients (7 both negative and 25 both positive); on the contrary, in 17 patients there was disagreement between FDG-PET/CT and t-WBS (P =ns). At short-term follow-up, Tg normalized in 19 (38.8%) patients and was unchanged or increased in 30 (61.2%). Of the 15 patients with negative FDG-PET/CT, 11 (73.3%) showed Tg normalization, whereas of the 34 patients with positive FDG-PET/CT, only 8 (23.5%) had Tg normalization (χ =8.9, P < .005). At multivariate analysis, FDG-PET/CT and Tg normalization at short-term follow-up were independent predictors of disease-free survival (χ =26.3, P < .0001), while Tg normalization was the only variable associated with overall survival χ =7.2, P < .01).

CONCLUSION

FDG-PET/CT in association with Tg normalization at short-term follow-up may be useful for long-term prognostic stratification in DTC patients.

Serum thyroglobulin reference intervals in regions with adequate and more than adequate iodine intake

The purpose of this study was to establish normal thyroglobulin (Tg) reference intervals (RIs) in regions with adequate and more than adequate iodine intake according to the National Academy of Clinical Biochemistry (NACB) guidelines and to investigate the relationships between Tg and other factors.A total of 1317 thyroid disease-free adult subjects (578 men, 739 nonpregnant women) from 2 cities (Guangzhou and Nanjing) were enrolled in this retrospective, observational study. Each subject completed a questionnaire and underwent physical and ultrasonic examination. Serum Tg, thyroid-stimulating hormone (TSH), thyroid peroxidase antibody (TPOAb), Tg antibody (TgAb), and urinary iodine concentration (UIC) were measured. Reference groups were established on the basis of TSH levels: 0.5 to 2.0 and 0.27 to 4.2 mIU/L.The Tg RIs for Guangzhou and Nanjing were 1.6 to 30.0 and 1.9 to 25.8 ng/mL, respectively. No significant differences in Tg were found between genders or among different reference groups. Stepwise linear regression analyses showed that TgAb, thyroid volume, goiter, gender, age, and TSH levels were correlated with Tg.In adults from regions with adequate and more than adequate iodine intake, we found that Tg may be a suitable marker of iodine status; gender-specific Tg RI was unnecessary; there was no difference between Tg RIs in regions with adequate and more than adequate iodine intake; and the TSH criterion for selecting the Tg reference population could follow the local TSH reference rather than 0.5 to 2.0 mIU/L.

Development and Validation of a New Low-Cost Enzyme-Linked Immunoassay for Serum and Dried Blood Spot Thyroglobulin

BACKGROUND

Thyroglobulin (Tg), a biomarker of iodine nutrition, can be measured on dried blood spots (DBS), which simplifies collection and transport in surveys. The World Health Organization recommends DBS-Tg for monitoring iodine status in children. It could also be a useful iodine biomarker during pregnancy. However, the Tg antibody (Ab) used in earlier DBS-Tg assays is no longer commercially available. The aims of the present study were: (i) to develop a new low-cost serum and DBS-Tg sandwich enzyme-linked immunosorbent assay for assessment of Tg in population studies; (ii) to check the stability of DBS-Tg during long-term storage; and (iii) to assess within-subject variability in DBS-Tg.

METHODS

Serum and DBS samples were measured from healthy pregnant women (n = 424) with the new assays, as well as the Immulite 2000 (Siemens), including TgAb positive (n = 150) and TgAb negative (n = 274) women. DBS-Tg stability was tested over 15 weeks of storage at -20 °C. Within-subject variability was evaluated over four weeks in four healthy adults.

RESULTS

Intra-assay and interassay variability was 4.4-7.3% and 10.1-12.9% for the new serum Tg assay, and 7.6-12.3% and 7.6-16.5% for the DBS-Tg assay. Correlation between the two serum methods was high (r = 0.68, p < 0.01). Assay performance in all women and those TgAb negative was comparable. Correlation between the new serum Tg assay and the DBS-Tg assay was high (r = 0.78, p < 0.01), and agreement expressed as a function of the average Tg concentration for the two methods (X) was 0.59X -4.59 μg/L. DBS-Tg was stable for 15 weeks stored at -20 °C. Within-subject variability in DBS-Tg was 21.1%. Reagents and antibodies costs for the new serum and DBS assays are ∼ US$1.

CONCLUSIONS

These new low-cost serum and DBS-Tg assays perform well over a wide range of Tg concentrations, and the field-friendly DBS assay may be particularly useful in population studies of iodine nutrition.

Thyroglobulin measurement by highly sensitive assays: focus on laboratory challenges

Differentiated thyroid cancer (DTC) is the most common endocrine cancer and its incidence has increased in recent decades. The initial treatment consists of total thyroidectomy followed by ablation of thyroid remnants by radioiodine in most cases. As thyroid cells are the only source of thyroglobulin (Tg), circulating Tg serves as a biochemical marker of persistent or recurrent disease in the follow-up of DTC. Due to the suboptimal clinical detection rate of older Tg assays endogenous or exogenous thyrotropin (TSH) stimulations are recommended for unmasking occult disease. However, the development of new Tg assays with improved analytical sensitivity and precision at low concentrations now allows detection of very low Tg concentrations, reflecting minimal amounts of thyroid tissue, even without the need for TSH stimulation. Even if the use of these assays still has not found its way in current clinical guidelines, such assays are now increasingly used in clinical practice. As serum Tg measurement is a technically challenging assay and criteria to define a ‘highly sensitive’ assay may be different, a good knowledge of the technical difficulties and interpretation criteria is of paramount importance for both clinical thyroidologists, laboratory physicians and scientists involved in the care of DTC patients.

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.

The role of FDG-PET/CT in differentiated thyroid cancer patients with negative iodine-131 whole-body scan and elevated anti-Tg level

AIM

In the follow-up of differentiated thyroid cancer (DTC) after a successful total-near total thyroidectomy and I-131 ablation therapy, anti-thyroglobulin antibodies (anti-Tg) may be persistently or progressively increased in the patients with an undetectable serum thyroglobulin (Tg) level. In these cases, further investigation was performed to search for recurrence/metastases. The aim of our study was clarifying the role of FDG-PET/CT in detecting recurrence/metastasis in patients with DTC with negative serum Tg and elevated anti-Tg level.

MATERIALS AND METHODS

A total of 40 patients (32 female, 8 male; mean age: 43.15 years (22-65); mean age at diagnosis: 39.08 (16-64)) with DTC who had undetectable serum Tg and elevated anti-Tg level after a successful initial therapy were included in the study. All of the patients had serum anti-Tg of >40 IU/ml and underwent FDG-PET/CT to search for recurrence/metastasis.

RESULTS

Twenty patients (50 %) had recurrence/metastasis on FDG-PET/CT while the other 20 had no pathologic findings. Of the 20 patients who had positive FDG-PET/CT, 12 had a histopathological final diagnosis of which 11 were true positive (TP) and 1 was false positive (FP). On the other hand, 16 of the 40 patients had a histopathological final diagnosis of which 11/16 had TP, 1/16 FP, 3/16 false negative (FN) and 1/16 true negative (TN) findings by PET/CT. The final diagnosis was made by clinical follow-up in the remaining 24 patients. Of these, 8 patients were PET positive, and in 1 (12.5 %) of 8 patients a decrease in serum anti-Tg level, in 2 (25 %) patients a saw-toothed pattern and in 5 (62.5 %) a progressive increase in the serum anti-Tg level were noted during the follow-up. Of the 16 of 24 patients who were diagnosed by clinical follow-up, in 8 a (50 %) decrease in serum anti-Tg level, in 6 (37.5 %) a saw-toothed pattern, and in 2 (12.5 %) a progressively increased anti-Tg level was seen. Of the 40 patients, 14 (35 %) had a diagnosis of recurrence/metastasis finally, with PET/CT detecting 11 (78.6 %) of them.

CONCLUSION

The value of a persistently or progressively increased serum anti-Tg level in the follow-up of DTC in the prediction of recurrence/metastasis is controversial. However, it is reported that FDG-PET can be useful in the detection of recurrence/metastasis. We conclude from the available data that PET/CT can be effectively used in the detection of recurrence/metastasis in the follow-up of patients with DTC and negative serum Tg and a persistently/progressively increased anti-Tg level. Besides, one half of the patients were FDG negative, meaning that further studies are needed to assess the prognostic-clinical value of PET negativity.

Thyroglobulin measurement using highly sensitive assays in patients with differentiated thyroid cancer: a clinical position paper

Differentiated thyroid cancer (DTC) is the most common endocrine cancer and its incidence has increased in recent decades. Initial treatment usually consists of total thyroidectomy followed by ablation of thyroid remnants by iodine-131. As thyroid cells are assumed to be the only source of thyroglobulin (Tg) in the human body, circulating Tg serves as a biochemical marker of persistent or recurrent disease in DTC follow-up. Currently, standard follow-up for DTC comprises Tg measurement and neck ultrasound combined, when indicated, with an additional radioiodine scan. Measurement of Tg after stimulation by endogenous or exogenous TSH is recommended by current clinical guidelines to detect occult disease with a maximum sensitivity due to the suboptimal sensitivity of older Tg assays. However, the development of new highly sensitive Tg assays with improved analytical sensitivity and precision at low concentrations now allows detection of very low Tg concentrations reflecting minimal amounts of thyroid tissue without the need for TSH stimulation. Use of these highly sensitive Tg assays has not yet been incorporated into clinical guidelines but they will, we believe, be used by physicians caring for patients with DTC. The aim of this clinical position paper is, therefore, to offer advice on the various aspects and implications of using these highly sensitive Tg assays in the clinical care of patients with DTC.

Thyroglobulin as a biomarker of iodine deficiency: a review

BACKGROUND

Thyroglobulin, produced exclusively by the thyroid gland, has been proposed to be a more sensitive biomarker of iodine status than thyrotropin or the thyroid hormones triiodothyronine and thyroxine. However, evidence on the usefulness of thyroglobulin (Tg) to assess iodine status has not been extensively reviewed, particularly in pregnant women and adults.

SUMMARY

An electronic literature search was conducted using the Cochrane CENTRAL, Web of Science, PubMed, and Medline to locate relevant studies on Tg as a biomarker of iodine status. Since urinary iodine concentration (UIC) is the recommended method to assess iodine status in populations, only studies that clearly reported both Tg and UIC were included. For the purpose of this review, a median Tg <13 μg/L and a median UIC ≥100 μg/L (UIC ≥150 μg/L for pregnant women) were used to indicate adequate iodine status. We excluded studies conducted in subjects with either known thyroid disease or those with thyroglobulin antibodies. The search strategy and selection criteria yielded 34 articles of which nine were intervention studies. The majority of studies (six of eight) reported that iodine-deficient pregnant women had a median Tg ≥13 μg/L. However, large observational studies of pregnant women, including women with adequate and inadequate iodine status, as well as well-designed intervention trials that include both Tg and UIC, are needed. In adults, the results were equivocal because iodine-deficient adults were reported to have median Tg values of either <13 or ≥13 μg/L. Only studies in school-aged children showed that iodine-sufficient children typically had a median Tg <13 μg/L. Some of the inconsistent results may be partially explained by the use of different methodological assays and failure to assess assay accuracy using a certified reference material.

CONCLUSIONS

These data suggest that Tg does hold promise as a biomarker of iodine deficiency. However, it is associated with limitations. A median Tg cutoff of 13 μg/L warrants further investigation, particularly in adults or pregnant women, as there is a lack of both observational and intervention studies in these groups.

The additive clinical value of 18F-FDG PET/CT in defining the recurrence of disease in patients with differentiated thyroid cancer who have isolated increased antithyroglobulin antibody levels

AIM

The aim of this study was to investigate the additive clinical value of 18F-FDG PET/CT in defining the recurrence of disease in patients with differentiated thyroid cancer (DTC) who have isolated increased antithyroglobulin antibody (TgAb) levels with undetectable thyroglobulin (Tg) levels and negative 131I whole-body scintigraphy (wbs).

MATERIALS AND METHODS

Clinical follow-up data of 231 patients with DTC who underwent 18F-FDG PET/CT between June 2006 and March 2011 were evaluated retrospectively. There were a total of 48 patients who underwent 18F-FDG PET/CT for isolated increased serum TgAb levels. When 17 patients who have lymphocytic thyroiditis were excluded, the remaining 31 patients [27 women and 4 men; mean (SD) age, 50.29 (15.2) y] were included in this study. The inclusion criteria were undetectable serum Tg and increased TgAb levels under the condition of thyroid-stimulating hormone greater than 30 IU/mL with negative 131I wbs and absence of pathologic findings in neck ultrasound and thoracic CT if performed. Findings from the 18F-FDG PET/CT were compared with the clinical follow-up data and the results of histopathologic examinations.

RESULTS

Results of 18F-FDG PET/CT were negative in 15 and positive in 16 patients. Sixteen FDG-positive sites (15 lymph nodes and 1 bone) were seen in 16 patients who had positive findings in 18F-FDG PET/CT. In the comparison with 18F-FDG PET/CT findings and clinical follow-up data and histopathologic examination results, 4, 12, 2, and 13 patients were false-positive, true-positive, false-negative and true-negative retrospectively. In the receiver operating characteristic analysis, a 5.4 cutoff SUVmax value was calculated with 82% sensitivity and 81% specificity in distinguishing malignant and benign lesions. As a result, the sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of 18F-FDG PET/CT in the detection of recurrent disease were calculated as 75%, 76%, 75%, 86%, and 80%, respectively.

CONCLUSIONS

Isolated increased TgAb levels might be a predictor of the recurrent DTC and 18F-FDG PET/CT might be an additive imaging method in detecting the recurrent disease in patients with DTC who have increased TgAb levels with undetectable Tg levels and negative 131I wbs.

Measuring Thyroglobulin Concentrations in Patients with Differentiated Thyroid Carcinoma

Thyroid carcinomas are the most common malignant endocrine tumors. Thyroglobulin (Tg), a specific thyroid protein, is the most important tumor marker in thyroid oncology. After total thyroidectomy or radioiodine therapy, detectable or increasing serum Tg levels in patients with differentiated thyroid carcinoma indicate persistence of active thyroid tissue or cancer recurrence. Serum Tg concentration primarily reflects three variables: the mass of differentiated thyroid tissue present; the degree of thyrotropin receptor stimulation and the intrinsic ability of the tumor to synthesize and secrete Tg. Measurement of serum Tg by current immunometric (IMA) and radioimmunological (RIA) assays encounters some methodological problems which can diminish its clinical importance. Discrepancy between the results for Tg using different methods may be caused by: different reference materials, specific properties of the primary and secondary antibodies for antigenic determinants on Tg and diverse binding affinities of these epitopes, together with interference by serum factors (usually antibodies to Tg (TgAb)) with the primary and secondary Tg antibodies from the diagnostic set. In the presence of endogenous TgAb, Tg values measured by immunoradiometric assay (IRMA) and similar assays are usually lower than the real concentrations, while in RIA apparently lower or higher results can be obtained. Falsely low values may lead to delay in necessary treatment, while an inappropriately high Tg value can cause patient anxiety and unnecessary scans. Despite current methodological limitations, serum Tg measurement is a useful test for determining worsening disease and monitoring the effects of therapy in patients who have undergone surgery for differentiated thyroid carcinoma.

Comparison of the influence of thyroglobulin antibodies on serum thyroglobulin values from two different immunoassays in post surgical differentiated thyroid carcinoma patients

Measurement of serum thyroglobulin (Tg) is a highly specific test in the management of patients with differentiated thyroid cancer (DTC) after surgical treatment. The aim of our study was to evaluate and compare Tg levels in these patients found by radioimmunoassay (RIA) and immunoradiometric assay (IRMA) and to assess the influence of Tg antibodies (TgAbs) on the values obtained for Tg concentration. Both Tg and TgAb were determined postoperatively in the serum of 71 DTC patients using RIA Tg-PEG (INEP) and Tg IRMA (CIS) for Tg, together with TgAb (CIS) for circulating endogenous anti-TgAbs. The obtained concentrations were evaluated statistically. We found a significant difference of Tg concentrations between paired samples from the IRMA and RIA, although the intermethod comparison yielded satisfactory concordance of the two assays (Spearman correlation coefficient -0.792). Positive TgAb was found in 28.2% of the serum samples analyzed. Spearman rank correlation analysis revealed a significant negative relationship between serum TgAb and Tg level measured by IRMA (P=0.02), but not by RIA (P=0.417). On the other hand, our clinical data revealed that 1/18 and 3/18 patients with proven lymph node metastasis had Tg values below the detection limit by RIA and IRMA assay, respectively. Their sera were TgAb positive. We concluded that RIA was less prone to influence of TgAb than IRMA. As the presence of TgAbs may interfere in Tg measurement irrespective of the method selected for determination, this should be considered during the clinical management of these patients.

Measuring thyroglobulin and thyroglobulin autoantibody in patients with differentiated thyroid cancer

Measurement of serum thyroglobulin is primarily used as a tumor marker in the postoperative management of patients with differentiated thyroid cancer. Unfortunately, the technical quality of current thyroglobulin assay methods varies and influences the clinical utility of this test. Two different methodologic approaches are used to measure serum thyroglobulin: the original competitive radioimmunoassay methodology and noncompetitive immunometric assay methods. Although the newer immunometric assays offer the technical benefits of eliminating the use of isotopes, using smaller specimen volumes, and having higher sensitivity potential, shorter turnaround times and the convenience of automation, immunometric assays also have a higher propensity for interference from both thyroglobulin autoantibodies and heterophilic antibodies, if present in the specimen. It is critical that physicians understand the technical limitations inherent in thyroglobulin measurement in order to effectively use this test for the postoperative management of patients with differentiated thyroid cancers.

Thyroglobulin reference values in a pediatric infant population

Few reports have addressed normal serum thyroglobulin (Tg) values in newborns and infants. In the present study, serum Tg was measured in 228 normal children (110 females and 118 males) aged from 3 to 180 days of life, all presenting normal age-related serum thyrotropin (thyroid-stimulating hormone [TSH]) values and negative anti-Tg and antithyroperoxidase antibodies. Serum Tg was measured by Radioimmunoassay (RIA) (two methods) and Immunometricassay (IMA) (three methods). Mean Tg values measured by the five methods exhibited among-method biases, although a significant positive correlation was observed. Serum Tg levels measured by the five methods showed a correlation with age, but not with TSH or gender. During the first days of life, relatively high mean Tg levels were observed, which progressively decreased until they reached a plateau. Therefore, with the aim of establishing reference values, the population was separated into two age groups: from 3 to 15 days of life (group A) and from 16 to 180 days of life (group B). Mean Tg concentration in group A was statistically higher than in group B. Tg centile distributions were calculated with the aim of establishing the normal levels of serum Tg for each method. We conclude that for a correct interpretation of serum Tg levels, the age and the methods used should be considered.

Thyroglobulin (Tg) recovery testing with quantitative Tg antibody measurement for determining interference in serum Tg assays in differentiated thyroid carcinoma

BACKGROUND

Thyroglobulin (Tg) measurements are complicated by interference from Tg autoantibodies (TgAbs) or heterophilic antibodies (HAMAs). We used a new automated immunochemiluminometric assay (ICMA) with Tg recovery (TgR) on the Nichols Advantage platform to reassess the clinical utility of recovery testing in detecting interference in serum Tg measurement in patients with differentiated thyroid carcinoma.

METHODS

We used 2 TgAb methods to detect Tg measurement interference with TgR and quantitative TgAb measurement in sera from 127 patients. In a limited number of samples, we used an RIA as comparison method because it appeared to be minimally affected by TgAb.

RESULTS

Prevalence of TgAbs was 13% (17 of 127) in either 1 or both TgAb assays. A compromised TgR (<70%) corresponded with TgAb positivity in either TgAb assay for 10 of 11 samples (91%), whereas a normal TgR (> or =70%) corresponded with TgAb negativity in both assays for 95 of 101 samples (94%). In 6 TgAb-positive sera with TgR within the reference interval, there were no discrepancies between RIA and ICMA results. We obtained discordant RIA and ICMA results for 6 of 9 TgAb-positive sera with decreased TgR. In 1 TgAb-negative sample, the Tg result was falsely increased because of interference by HAMAs, as shown by an overrecovery of 126%.

CONCLUSIONS

The Nichols Advantage TgR assay is a valuable complementary method to overcome the technical problem of interference by TgAbs or HAMAs in TgAb assays. Further studies are needed to confirm the potential added value of this TgR assay.

Antithyroglobulin antibodies in patients with differentiated thyroid carcinoma: methods of detection, interference with serum thyroglobulin measurement and clinical significance

Antithyroglobulin antibodies (TgAb) were measured using a chemiluminescent immunoassay (ICMA) and an agglutination test. TgAb laboratory and clinical interference with Tg measurements were assessed. The course of TgAb concentration and disease status were compared during 3 years after initial treatment. The agglutination test failed to detect all titers < 10IU/mL (ICMA). Interference from TgAb was common at high titers, but even low antibody titers (< 5IU/mL) were able to interfere with Tg measurement. Cases of distant metastases with undetectable Tg (by IRMA) and those apparently free of disease and without thyroid remnants with Tg> 2ng/ml (by RIA) were identified among patients with TgAb. The exogenous Tg recovery test was normal (> 80%) by the two methods in 22% of patients with TgAb and confirmed laboratory interference. Absence of reduction in TgAb levels was a marker of persistent disease. In conclusion, TgAb should be determined by immunoassays; interference with Tg measurements occurred mainly but not always at high concentrations, with a normal Tg recovery test not excluding this interference. The behavior of TgAb is related to disease persistence or cure.

Thyroglobulin: a specific serum marker for the management of thyroid carcinoma

Thyroglobulin measurements in tissue and serum play an integral role in the evaluation of patients who have thyroid cancer. Immunohistochemical detection of thyroglobulin in surgical specimens is useful in the differential diagnosis of tumors of unknown origin; however, the most important application of thyroglobulin measurement in clinical practice is in the postsurgical management of differentiated thyroid cancer. Serum thyroglobulin is a highly specific and sensitive tumor marker for detecting persistent or recurrent thyroid cancer and for monitoring clinical status. The reappearance of circulating thyroglobulin after total thyroid ablation is pathognomonic for the presence of tumor. The measurement of thyroglobulin in serum is challenging, however, and several analytical problems limit assay performance. Thyroglobulin autoantibody interference is a particularly significant concern that requires all thyroglobulin samples to be screened for their presence. No immunoassay is totally free from interference by thyroglobulin autoantibodies. Measurement of thyroglobulin mRNA to detect circulating tumor cells may help to overcome some of the limitations of current protein-detection methods; serum thyroglobulin will continue to remain the "gold standard." The complex functional features of thyroid carcinomas make sole reliance upon any one diagnostic technique, including thyroglobulin assessments, potentially misleading. Thyroglobulin measurements are a critical component of a multifaceted diagnostic approach to this disease.

Diagnostic value of serum thyroglobulin measurements in the follow-up of differentiated thyroid carcinoma, a structured meta-analysis

OBJECTIVE

To investigate to what extent thyroid remnant ablation and withdrawal from thyroxine are required to achieve sufficient accuracy of serum thyroglobulin (Tg) measurements as an indicator of tumour recurrence in the follow-up of patients with differentiated thyroid carcinoma.

DESIGN AND METHODS

We conducted a meta-analysis of the literature from 1975 to 2003 on serum Tg measurements in the follow-up of differentiated thyroid carcinoma. In a computer-based search, we initially found 915 articles that were finally narrowed down to 120. These 120 papers were subjected to strict in/and exclusion criteria, leaving 46 articles (totalling 9094 patients). Data from these articles were extracted in a structured fashion and were grouped according to initial therapy, TSH status, Tg assay method and definition of a 'gold standard'. Original 2 x 2 tables were pooled by summary receiver operating characteristic curve analysis (sROCa), best estimates of sensitivity and specificity being obtained by the combination of sROCa and Mantel-Haenszel odds ratios.

RESULTS

Despite considerable differences between series in laboratory and clinical methodology, we consistently found higher specificity for Tg measurements after thyroid remnant ablation than after surgery alone. Highest pooled sensitivity 0.961 +/- 0.013 (SE) was found for immunometric assay (IMA) after thyroid remnant ablation and thyroid hormone withdrawal, at a specificity of 0.947 +/- 0.007. Pooled sensitivity decreased significantly if ablated patients were tested while on thyroid hormone (0.778 +/- 0.023, at a specificity of 0.977 +/- 0.005). Significantly decreased pooled specificity was found in patients who did not undergo remnant ablation (sensitivity 0.972 +/- 0.023, at a specificity of 0.759 +/- 0.028). If recombinant human TSH (rhTSH) stimulation was used as a substitute for thyroxine withdrawal, sensitivity remained high (0.925 +/- 0.018) while specificity decreased to 0.880 +/- 0.013. In all analyses, specificity of Tg would decrease when unspecified activity in the thyroid region at scintigraphy was considered benign, whereas sensitivity decreased when such activity was considered malignant.

CONCLUSION

This study confirms that the best accuracy of Tg-guided follow-up in patients treated for differentiated thyroid carcinoma is obtained if treatment includes remnant ablation, and Tg testing is performed while off thyroxine.

Discordant serum thyroglobulin results generated by two classes of assay in patients with thyroid carcinoma: correlation with clinical outcome after 3 years of follow-up

BACKGROUND

Serum thyroglobulin measurement is an integral part of monitoring patients with thyroid carcinoma, but analytic problems pose serious difficulties in the utility of this test.

METHODS

Between 1997 and 1998, serum samples from 83 patients with differentiated thyroid carcinoma were collected. Serum thyroglobulin was assayed by both radioimmunoassay and by an immunoradiometric assay. The disease status of patients with discordant serum thyroglobulin results was assessed in June 2001. Therefore, the predictive value of a single thyroglobulin measurement was assessed by evaluating the clinical status of patients 3 years later.

RESULTS

Discordant serum thyroglobulin results were noted in 17 (20.4%) patients. Of the 17 patients with discordant results, 16 had adequate clinical follow-up data. Of these 16 patients, 11 patients had detectable levels of serum thyroglobulin by immunoradiometric assay (range, 1.4-350 microg/L) whereas levels were undetectable by radioimmunoassay (< 1 microg/L). All 11 patients had evidence of metastases 3 years later. Two patients had undetectable serum thyroglobulin levels using the immunoradiometric assay (< 1 microg/L), whereas they had detectable levels using radioimmunoassay (serum thyroglobulin 7.2-30 microg/L). The serum samples from both patients had normal recoveries and positive antithyroglobulin antibodies. Both patients developed metastases 3 years later.

CONCLUSIONS

False-negative serum thyroglobulin results were significantly higher with the radioimmunoassay method compared with the immunoradiometric assay. The immunoradiometric assay is more reliable than the radioimmunoassay, particularly in patients who have no thyroglobulin antibodies. This finding is novel in that traditional immunoradiometric assay systems compared with radioimmunoassays usually have a higher incidence of false-negative results when assessed against clinical status. The immunoradiometric assay is subject to false-negative results in some patients with thyroglobulin antibodies, even when recovery experiments indicate the absence of interference. Thyroglobulin antibodies should be measured in all patients with differentiated thyroid carcinoma and if positive, results should be interpreted with extreme caution.

Clinical significance of elevated level of serum antithyroglobulin antibody in patients with differentiated thyroid cancer after thyroid ablation

OBJECTIVE

This study was designed to investigate whether an elevated serum antithyroglobulin antibody (TgAb) reflects cancer recurrence in thyroglobulin (Tg)-undetectable patients with differentiated thyroid carcinoma (DTC) after thyroid ablation.

DESIGN

We measured serum TgAb level and evaluated the disease status in 226 DTC patients who had undergone remnant ablation and showed an undetectable Tg result as assessed by immunoradiometric assay.

MEASUREMENTS

Radioligand assay of TgAb was performed. Recurrence was assessed by 131I scan, 18F-fluorodeoxyglucose positron emission tomography, sonography, computed tomography, or by surgical operation.

RESULTS

Fifty-one patients (22.6%) of the Tg-undetectable patients showed positive TgAb, and 25 (49.0%) of these were confirmed with recurrence. The recurrence rate of TgAb-positive patients was higher than that of TgAb-negative patients (3.4%; P < 0.0001). During follow-up, 73.1% of the disease-free patients showed spontaneously decreased TgAb levels. A total of 71.4% of patients with recurrent cancer, who showed responses to surgical operation or radio-iodine treatment, also showed a decreased TgAb level.

CONCLUSIONS

Persistently elevated TgAb levels appear to serve as a useful marker for recurrent or persistent DTC in patients with undetectable serum Tg results. Thus, the routine measurement of TgAb in such patient populations may be indicated.

Serum thyroglobulin measurement. Utility in clinical practice

Serum thyroglobulin measurement has greatly facilitated the clinical management of patients with differentiated thyroid cancer and a variety of other thyroid disorders. Thyroglobulin autoantibodies remain a significant obstacle to the clinical use of thyroglobulin measurement. The interpretation of any given thyroglobulin value requires the careful synthesis of all pertinent clinical and laboratory data available to the clinician. The diagnostic use of rhTSH-stimulated thyroglobulin levels has greatly facilitated the follow-up of low-risk patients with thyroid cancer. Although the measurement of thyroglobulin mRNA from peripheral blood is likely to affect the future management of these patients, it is expected that serum thyroglobulin measurement will continue to have a principal role in the care of patients with differentiated thyroid cancer.

Serum thyroglobulin measurements in differentiated thyroid cancer

In pathological states, the serum thyroglobulin (Tg) concentrations are generally high. Therefore, a serum assay of Tg levels is not useful for the differential diagnosis between benign or malignant disease in the preoperative period. Serum Tg measurements are a suitable marker in the follow-up of patients with differentiated thyroid carcinoma (DTC) during the postoperative period. After total thyroidectomy, serum Tg concentrations were found to be undetectable in subjects without evidence of residual thyroid tissue or metastases; however, detectable serum Tg levels in subjects on and off thyroid hormone suppressive therapy indicate the presence of residual or metastatic thyroid tissue. An increase in serum Tg levels during thyroid stimulating hormone (TSH) suppression indicates that further investigations are necessary.

Evaluation of the first automated thyroglobulin assay

The aim of this study was to investigate technical and analytical performance of the first automated thyroglobulin (Tg) assay (DPC-Immulite; Diagnostic Products Corporation, Los Angeles, USA). In imprecision studies using several human serum pools ranging from 21 to 58 replicates, a coefficient of variation of 9.0% was obtained at a mean Tg concentration of 0.84 ng/ml and of 6.1% at a Tg concentration of 62.1 ng/ml. In a method comparison with a non-automated assay (BRAHMS LUMItest Tg, BRAHMS, Berlin, Germany) using 383 sera of 303 patients with thyroid carcinoma, regression analysis according to Passing and Bablock yielded in the following equation: Immulite Tg = 1.6 x BRAHMS Tg-0.1 ng/ml (Pearson's r = 0.979). Sera obtained from 59 patients with thyroid carcinoma enabled comparative follow-up studies; in all cases qualitative agreement was found with regard to increase or decrease of serum Tg; in eight cases, however, Tg was detected with the Immulite assay but not with the BRAHMS assay. Further follow-up proved the presence of thyroid tissue in these patients. From these and further methodological data (dilution linearity, interference studies, carry-over study, high-dose hook properties, and short report time) it is concluded that the DPC-Immulite Tg assay meets the requirements of routine diagnostic use.

False positive 131I total body scan due to an ectasia of the common carotidis

A cervical accumulation of radioiodine at Total Body Scan (TBS) in a patient who had been thyroidectomized for a follicular thyroid carcinoma led to unnecessary radioiodine treatment. Thyroglobulin measurements indicated constantly low levels. Following ultrasound scanning of the neck, echo-doppler examination of the cervical vessels and angiography with 99Tc, this area of increased activity at TBS imaging was shown to be due to an ectasia of the right common carotidis causing blood stasis and reverse flow.

A new immunoradiometric assay (IRMA) system for thyroglobulin measurement in the follow-up of thyroid cancer patients

A new commercially available kit for thyroglobulin (Tg) measurement [immunoradiometric assay (IRMA) system based on monoclonal antibodies] was used in 479 patients with thyroid carcinoma. The effective working range was 1 ng/ml, and results were strongly correlated with our homemade radioimmunoassay (RIA). This IRMA method is less susceptible to interferences of auto-antibodies than our RIA. During thyroxine (T4) treatment, the Tg level was undetectable in 98% of patients after total thyroid ablation, in 91% after total thyroidectomy and in 42% after lobectomy only. In this situation, Tg was found in all patients with large metastases and in 88% of those with small metastases. Following T4 withdrawal, Tg was detectable in all patients with neoplastic disease and in 13% of those in complete remission after total thyroid ablation. In conclusion, Tg measured with this IRMA method appears to be a reliable marker of differentiated thyroid carcinoma.

Usefulness of the combined antithyroglobulin antibodies and thyroglobulin assay in the follow-up of patients with differentiated thyroid cancer

A total of 1050 patients with differentiated thyroid cancer (DTC) have been followed in the Thyroid Center of Padua by means of serum thyroglobulin (Tg) measured with IRMA method and anti-Tg antibodies (TgAb) assays. Circulating TgAbs were detected in 102 (9.7%) patients. In 32 of these 102, TgAbs were evaluated before and after total thyroidectomy and 131I ablation. In these patients no relationship was found between preoperative serum TgAb levels on the one hand and tumor stage at diagnosis or outcome of the disease on the other. During the follow-up, TgAb serum levels decreased or disappeared in 21 cases considered tumor-free, while they remained unchanged or even increased, in comparison with the preoperative ones, in 11 patients, 5 with proven metastases and 6 considered tumor-free. Evaluating the whole group of 102 TgAb-positive patients, we observed that TgAb serum levels, measured after thyroid ablation, were significantly higher in cases with metastases than in those considered tumor-free (653.0 +/- 196.9 vs 157.7 +/- 116.5 U/ml, m +/- SD, p less than 0.0001). In the group of patients with metastases and circulating TgAbs, Tg serum levels were elevated in 27% of cases on TSH-suppressive therapy and in 44% off therapy when nodal metastases were present, and in 67% of cases on TSH-suppressive therapy and in 83% off therapy when distant metastases were present.(ABSTRACT TRUNCATED AT 250 WORDS)

Low levels of serum thyroglobulin after withdrawal of thyroid suppression therapy in the follow up of differentiated thyroid carcinoma

We evaluated the reliability of very low serum thyroglobulin (Tg) levels (less than 3 ng/ml) obtained after withdrawal of thyroid suppression therapy in 224 patients without anti-Tg antibodies, who had undergone total thyroidectomy (125 patients) or thyroidectomy followed by 1 or more courses of 131I therapy (99 patients), by performing whole body scans after a therapeutic course of 131I given at the same time of Tg measurement. In 79 patients (35%) a positive scan, associated with a very low level of Tg, was noted. The 131I uptake was limited to the thyroid bed in 60 patients, but metastases were demonstrated in 19 patients (8.5%). These results are mainly explained by the much improved performance of scintigraphy after administration of therapeutic doses of 131I. In the majority of patients, especially those whose 131I uptake was limited to the thyroid bed, further scans were negative. Therefore, in these cases, negative Tg values can generally be considered an early indication of satisfactory evolution. However, in 8.5% of all cases, very low Tg levels were associated with metastases. Thus the follow up of thyroid cancer should not rely only upon Tg determination, even after suppression therapy withdrawal.

Clinical evaluation of serum thyroglobulin measurement using a commercial kit in the diagnosis of recurrent thyroid cancer

The value of serum thyroglobulin assay employing a kit manufactured by Diagnostic Products Corporation in the detection of recurrence of thyroid carcinoma in patients treated by thyroidectomy and ablative therapy was assessed by clinical follow-up and radioiodine scanning of 122 patients over a 2-year period. A total of 204 specimens were analysed. The assay was found to be sensitive and highly specific for the detection of recurrent thyroid carcinoma provided that lipemic sera are clarified by ultracentrifugation prior to measurement and that results from those patients who demonstrate positive serum antithyroglobulin antibodies are excluded. The predictive value of a serum thyroglobulin level above 20 pmol/L was 96% for recurrence of thyroid carcinoma. The predictive value for non-recurrence was 98% for serum thyroglobulin levels below 10 pmol/L. The specificity and sensitivity of the assay were poor for serum thyroglobulin levels between 10 and 20 pmol/L. In recurrence-free patients, the serum thyroglobulin levels were not changed by withdrawal of thyroid replacement therapy 4-7 weeks prior to sampling.

Differentiated follicle-derived thyroid carcinoma in children

Fifteen patients, 11 females and 4 males, aged 4-16 years with follicle-derived differentiated thyroid carcinoma treated at the Helsinki University Central Hospital during 1953 through 1984 are reported. Histologically 13 carcinomata were papillary, 1 follicular and 1 was suspected to be follicular carcinoma (atypic adenoma). Eleven (73%) had cervical lymphnode metastases and 4 (25%) pulmonary metastases as well. All patients were initially operated on; total thyroidectomy was performed in 11 and subtotal in 4 patients. In 5 patients there was invasion into the thyroid capsule, perithyroid tissues and blood vessels; 4 patients with pulmonary metastases belonged to this group. Postoperatively 5 patients received radioactive iodine, 4 patients external irradiation to the neck and 6 were given both types of radiation. Pulmonary metastases were treated with radioactive iodine. The patients have been given suppressive doses of thyroxine. The follow-up ranged from 3.5 to 33 years. One patient with extensive pulmonary metastases died 6 years after the initial treatment, all others are still alive. Twelve patients have been followed for 9 to 33 years, in 10 serum thyroglobulin was determined. Tg was undetectable in 9 patients when measured during thyroxin therapy; in 1 patient followed for 33 years, the dose was not suppressive, and there were no signs of disease and Tg in the normal range. In 2 patients Tg could not be determined but they had no signs of disease 18 and 22 years after initial treatment. It is, therefore, presumed that these patients, forming 80% of the material, are cured. Two patients followed for 3.5 years are still under treatment.(ABSTRACT TRUNCATED AT 250 WORDS)