Is there a role for an ultrasensitive thyroglobulin assay in patients with serum antithyroglobulin antibodies? A large (Australian) cohort study in differentiated thyroid cancer

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.

A Retrospective Cohort Study with Validation of Predictors of Differentiated Thyroid Cancer Outcomes

Background: The goal of radioactive iodine (RAI) in differentiated thyroid cancer (DTC) is to treat metastasis and reduce recurrence risk. International guidelines provide broad risk stratification to aid treatment decisions, but a more nuanced approach to individualize care is warranted. We developed a predictive risk model for DTC. Methods: We performed a retrospective multivariable analysis of 899 patients who received RAI after thyroidectomy at a quaternary center in Australia between 2008 and 2016. Collected data included age, gender, histology, stimulated thyroglobulin (sTg), and 8th American Joint Committee Cancer (AJCC) staging. The ATA Modified Initial Risk (ATA) was calculated retrospectively. Recurrence was defined as clinically significant progression requiring either surgical intervention or administration of a second activity of RAI. Synchronous metastasis was defined as distant metastasis (i.e., outside of the neck) that was present at the time of diagnosis on structural imaging or initial post-iodine treatment scan. The features significantly associated with synchronous metastasis or recurrence were employed in the generation of a predictive risk model. A separate cohort of 393 patients who received RAI in 2017-2021 was used for validation. Results: On multivariate analysis, sTg ≥10 μg/L, extrathyroidal extension (ETE) and lymph node involvement predicted recurrence. Independent of ATA, patients with sTg ≥10 μg/L had a shorter disease-free survival (DFS) than those with sTg <10 μg/L (p < 0.001). The ETE stratified by four histological categories was significantly associated with worse DFS (p < 0.001). In a subset of patients, the presence of thyroglobulin antibody (TgAb) did not influence recurrence in patients with sTg <10 μg/L. On multivariate analysis, widespread ETE, sTg ≥10 μg/L, multifocal papillary thyroid cancer and follicular thyroid cancer were positively associated with synchronous metastasis. A predictive risk model was developed to estimate synchronous metastasis/recurrence risk and validated successfully in the second cohort. Conclusions: Our novel predictive risk model modifies and extends ATA stratification by including sTg and ETE, which we found to be independent predictors of both recurrence and synchronous metastasis in DTC.

Early post-treatment risk stratification of differentiated thyroid cancer: comparison of three high-sensitive Tg assays

OBJECTIVE

To assess the diagnostic performance of three high-sensitive assays in a cohort of TgAb-negative and TgAb-positive differentiated thyroid cancer (DTC) patients.

DESIGN

Retrospective study on prospectively selected DTC patients.

METHODS

Serum samples from 154 DTC patients were obtained 6-12 months after radioiodine ablation and tested by Beckman, Roche, BRAHMS Tg and TgAb assays, respectively. Receiver operating characteristics curves for Tg were plotted using outcome over time as benchmark and assay-specific Tg thresholds were obtained for TgAb-negative and TgAb-positive patients.

RESULTS

The frequency of positive TgAb was 21, 20 and 20% for Beckman, Roche and BRAHMS, respectively. In TgAb-negative patients, clinical sensitivities and specificities of 100% and 85-95%, respectively, were observed across all assays. In TgAb-positive patients, clinical sensitivities and specificities of 80-100% and 92-96%, respectively, were observed using lower thresholds than in patients without TgAb.

CONCLUSIONS

Adopting appropriate thresholds, lower than those for TgAb-negative patients, is possible to reliably follow TgAb-positive patients using highly sensitive Tg assays.

Factors associated with serum thyroglobulin in a Ukrainian cohort exposed to iodine-131 from the accident at the Chernobyl Nuclear Plant

BACKGROUND

Serum thyroglobulin (Tg) is associated with the presence of thyroid disease and has been proposed as a biomarker of iodine status. Few studies have examined factors related to serum Tg in populations environmentally exposed to ionizing radiation and living in regions with endemic mild-to-moderate iodine deficiency.

METHODS

We screened 10,430 individuals who were living in Ukraine and under 18 years of age at the time of the 1986 Chernobyl Nuclear Power Plant accident for thyroid disease from 2001 to 2003. We estimated the percent change (PC) in serum Tg associated with demographic factors, iodine-131 thyroid dose, and indicators of thyroid structure and function using linear regression. We also examined these relationships for individuals with and without indications of thyroid abnormality.

RESULTS

Mean and median serum Tg levels were higher among participants with abnormal thyroid structure/function. Percent change in serum Tg increased among females, smokers and with older age (p-values<0.001), and Tg increased with increasing thyroid volume, and serum thyrotropin (p-values for trend<0.001). We found no evidence of significant associations between iodine-131 thyroid dose and Tg. Serum Tg levels were inversely associated with iodized salt intake (PC=-7.90, 95% confidence interval: -12.08, -3.52), and over the range of urinary iodine concentration, the odds of having elevated serum Tg showed a U-shaped curve with elevated Tg at low and high urinary iodine concentrations.

CONCLUSION

Serum Tg may be a useful indicator of population iodine status and a non-specific biomarker of structural and functional thyroid abnormalities in epidemiological studies.

Thyroglobulin Antibody Screen Prior to Mass Spectrometry Provides Measurable Cost Savings and Optimal Laboratory Utilization

OBJECTIVES

Liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods that allow accurate quantitation of thyroglobulin (Tg) in the presence of Tg antibodies (TgAbs) have recently become available. Due to cost differences between LC-MS/MS and immunoassay, some laboratories now offer a reflex test strategy that uses LC-MS/MS only for TgAb-positive samples. The goal of this study was to examine utilization of Tg testing strategies and cost savings.

METHODS

Test ordering patterns were examined for over 150,000 orders for TgAb and Tg in our laboratory. The average list price was determined from three separate commercial laboratories offering this testing.

RESULTS

Data showed that 89% of orders for Tg used the reflex test option, resulting in a savings of over $3 million compared with testing all samples by LC-MS/MS. Of the Tg by LC-MS/MS orders not using the reflex option, 1,663 also included a separate order for TgAb on the same patient sample, representing approximately $170,000 in potentially unnecessary costs from TgAb-negative samples.

CONCLUSIONS

Identifying situations to use more expensive testing methods (eg, LC-MS/MS) only when necessary, such as for TgAb-positive patients, leads to considerable cost savings and a more economical use of valuable health care resources.

Can the follow-up of patients with papillary thyroid carcinoma of low and intermediate risk and excellent response to initial therapy be simplified using second-generation thyroglobulin assays?

OBJECTIVE

In view of the low probability of recurrence, the cost-effective follow-up of patients with papillary thyroid carcinoma (PTC) of low or intermediate risk and excellent response to initial therapy represents a challenge. This study evaluated the cases of structural recurrence among these patients.

PATIENTS

The sample comprised 578 patients with PTC of low or intermediate risk, who were submitted to total thyroidectomy with or without (131) I therapy and exhibited an excellent response to initial therapy defined based on nonstimulated thyroglobulin (Tg) ≤0·2 ng/ml and negative neck ultrasonography (US).

RESULTS

Twelve patients (2%) showed structural recurrence. At the time when recurrence was 'confirmed', Tg elevation had not occurred in only two patients, one with lymph node metastases <1 cm detected by US and the other with pulmonary metastases. Antithyroglobulin antibodies (TgAb) were undetectable in both patients. The first alteration observed in patients with recurrence was Tg elevation in six patients, Tg elevation associated with suspicious US in three, and suspicious US in two. An increase in TgAb was not the first alteration in any of the patients. Among the 560 patients who continued to have Tg ≤ 0·2 ng/ml, US permitted the detection of only one neck recurrence. Measurement of TgAb did not detect any recurrence.

CONCLUSION

Our results confirm that in patients with PTC of low or intermediate risk an excellent response to initial therapy can be defined based on nonstimulated Tg ≤ 0·2 ng/ml. Follow-up consisting only of clinical examination and periodic measurement of Tg with a second-generation assay may be sufficient.

Comparison of Thyroglobulin Measurements Using Three Different Immunoassay Kits: A BRAMHS Tg-Plus RIA Kit, a BRAMHS hTg Sensitive Kryptor Kit, and a Beckman Coulter ACCESS Immunoassay Kit

BACKGROUND

Second-generation thyroglobulin immunometric assays (Tg-IMAs) have been developed with improved sensitivity. Our aim was to compare the diagnostic value of Tg-IMA measurements using a Kryptor (BRAHMS AG) kit (Tg-K) and an ACCESS (Beckman Coulter) kit (Tg-A) with that of the first-generation Tg measurement using a Tg-plus (BRAHMS AG) kit (Tg+).

METHODS

We enrolled 82 differentiated thyroid cancer patients who underwent total thyroidectomy with radioactive iodine remnant ablation and who underwent diagnostic whole body scan using recombinant human thyroid stimulating hormone (rhTSH). The Tg+, Tg-K, and Tg-A were measured before rhTSH administration during levothyroxine treatment (suppressed Tg) from the same sample. Serum Tg+ was measured after rhTSH stimulation (stimulated Tg).

RESULTS

Suppressed Tg+ was more significantly correlated with suppressed Tg-K (R²=0.919, P<0.001) than with suppressed Tg-A (R²=0.536, P<0.001). The optimal cut-off values of suppressed Tg+, Tg-K, and Tg-A for predicting stimulated Tg+ of 1 ng/mL were 0.3, 0.2, and 0.2 ng/mL, respectively. The sensitivity, specificity, and accuracy of suppressed Tg+ were 67%, 100%, and 90%, respectively; those of suppressed Tg-K were 83%, 90%, and 88%; those of suppressed Tg-A were 96%, 82%, and 87%, respectively. The positive predictive and negative predictive values of Tg+ were 100% and 87%, respectively; those of Tg-K were 79% and 92%; and those of Tg-A were 73% and 98%.

CONCLUSION

We could not clearly demonstrate which kit had better diagnostic performance after comparison of first-generation Tg measurements with Tg-IMA measurements. Also, there were kit-to-kit variations between Tg-IMA kits. Suppressed Tg measured by Tg-IMA was insufficient to completely substitute for a stimulated Tg measurement.