The Roche Elecsys and Siemens-Centaur thyroglobulin autoantibody assays show comparable clinical performance to the recently unavailable Beckman-Coulter access thyroglobulin autoantibody assay in identifying samples with potentially false-low thyroglobulin measurements due to thyroglobulin autoantibody interference

Clinical implications of changing thyroglobulin and antithyroglobulin antibodies analytical methods in the follow-up of patients with differentiated thyroid carcinoma

BACKGROUND AND AIMS

Patients' response to treatment in differentiated thyroid cancer (DTC) is classified according to serum thyroglobulin concentrations (Tg), usually using the American Thyroid Association guidelines and considering potential interfering anti-thyroglobulin antibodies (Ab-Tg). We aim to evaluate the clinical implications of changing Tg and Ab-Tg quantification method.

MATERIAL AND METHODS

Tg and Ab-Tg were quantified in 82 serum samples (60 from DTC patients) by Elecsys and Access immunoassays.

RESULTS

Elecsys immunoassay rendered higher values of Tg than Access: mean bias 5.03 ng/mL (95%CI:-14.14-24.21). In DTC patients, there was an almost perfect agreement for response classification (kappa index = 0.833). Discrepancies appeared in patients with undetermined response, with a more tendency to subclassification with Access. Ab-Tg showed a poor correlation (r = 0.5394). When Elecsys cut-off was reduced to 43 IU/mL, agreement for positive/negative classification improved from a kappa index of 0.607 to 0.650. Prospective study with personalized follow-up showed that only 6.3% of Tg results required an analytical confirmation, being confirmed 93% of them.

CONCLUSIONS

Despite the biases observed, clinical impact of an analytical change is minimal in patients' management. However, cautious and personalized follow-up period after the change is still mandatory, especially in patients with Tg levels between 0.2 and 1 ng/mL.

Multicentre clinical evaluation of the new highly sensitive Elecsys® thyroglobulin II assay in patients with differentiated thyroid carcinoma

OBJECTIVE

A highly sensitive thyroglobulin assay (Elecsys® Tg II, Roche Diagnostics, Penzberg, Germany) has become available for monitoring patients with differentiated thyroid cancer (DTC). Here, we evaluated the clinical performance of Elecsys® Tg II assay in a multicentre patients series and compare it with the established Access® Tg assay (Beckman Coulter, Brea, CA, USA).

DESIGN

Retrospective analysis on prospectively selected patients in four thyroid cancer referral centres with uniform DTC management.

PARTICIPANTS

All DTC cases diagnosed, treated and followed up in four tertiary referral centres for thyroid cancer since January 2005 (n = 1456) were retrieved, and predefined selection criteria were applied to prevent relevant enrolment biases. A series of 204 patients was finally selected for this study.

MEASUREMENTS

Samples had been stored at -80°C. Tg was measured by fully automated immunometric Elecsys® Tg II and Access® Tg assays in a centralized laboratory.

RESULTS

Two hundred and four DTC were finally included. Of these, 10.8% had structural recurrence (sREC), and 81.4% showed no evidence of disease (NED) at the end of follow-up. There was a significant analytical bias between methods that cannot be used interchangeably. Using ROC curve analysis, the best basal and rhTSH-stimulated Tg cut-offs to detect sREC were 0.41 μg/L and 1.82 μg/L for Elecsys® and 0.36 μg/L and 1.62 μg/L for Access® assay, respectively. Using Cox proportional hazard regression, Tg was the only independent predictor of cancer relapse.

CONCLUSIONS

Using appropriate assay-specific cut-offs, the clinical performance of the Elecsys® Tg II assay was comparable to that provided by the well-established Access® Tg assay.

Variation in Results Release and Patient Portal Access to Diagnostic Test Results at an Academic Medical Center

BACKGROUND

Electronic health records (EHRs) are commonplace in industrialized countries. Many hospitals are granting their patients access to their medical information through online patient portals. In this report, we describe a retrospective analysis of patient access to diagnostic test results released through the patient portal (MyChart; Epic, Inc.) at a state academic medical center.

METHODS

We analyzed 6 months of data for anatomic pathology, clinical laboratory, and radiology test results to evaluate variations in results release (automated vs. manual) and subsequent patient access to the institutional patient portal. During this period, diagnostic test results were released for all patient encounters including inpatient units, outpatient clinics, and the emergency department.

RESULTS

Manual results release by providers before automated release time occurred most commonly in the outpatient setting. The highest rates of access of diagnostic test results occurred for outpatients (about 30% overall view rate), females (two times or more compared to males in nearly every age bracket), and 20-45-year-old. Access rates of diagnostic tests in the emergency department or inpatient units were <10% across all populations. Access of diagnostic test results was very low for 12-17-year-old, likely influenced by institutional policies limiting parental proxy access within this pediatric age range. Approximately 20% of outpatient laboratory results were viewed by patients within 8 h of release from the EHR to the patient portal and 10% within 2 h of release.

CONCLUSIONS

Patient accessing of diagnostic test results were generally higher for females, outpatients, and 20-45-year-old. Approximately, 20% of outpatient results were viewed quickly by patients after release to the EHR.

Serial post-surgical stimulated and unstimulated highly sensitive thyroglobulin measurements in low- and intermediate-risk papillary thyroid carcinoma patients not receiving radioactive iodine

The purpose of this study was to determine the natural temporal trends of serial thyroglobulin (Tg) among low/intermediate-risk PTC patients not receiving radioactive iodine (RAI) using TSH-stimulated Tg (Stim-Tg) and unstimulated highly sensitive Tg (u-hsTg). We prospectively analyzed serial Stim-Tg measurements after total thyroidectomy ± therapeutic central neck dissection among 121 consecutive low/intermediate-risk PTC patients who did not receive RAI, of whom 104 also had serial u-hsTg measurements available. Median follow-up was 6.5 years with Stim-Tg measurements commencing 3 months after surgery and u-hsTg commencing 1.8 years after surgery (when the assay became available). TSH stimulation was performed with 9-day T3 withdrawal, 22-day T4 withdrawal, or using recombinant human TSH (rhTSH). To account for within-patient correlations of repeated Tg measurements, temporal trends in Stim-Tg and u-hsTg were assessed using Generalized Estimating Equations. Stim-Tg models were adjusted for the method of TSH stimulation, whereas the u-hsTg models were adjusted for concurrent TSH level. Linear regression modeling was used to assess the trend in serial Stim-Tg and u-hsTg measurements as a function time from time of surgery throughout the duration of follow-up. The main outcome measured was the change in u-hsTg and Stim-Tg measurements over time. A total of 337 Stim-Tg (2.8/patient) and 602 u-hsTg (5.8/patient) measurements were analyzed. Among the 337 Stim-Tg measurements, Stim-Tg was assessed using rhTSH in 202 (60 %), T4 withdrawal in 41 (12 %), and T3 withdrawal in 94 (28 %) measurements. The overall mean ± 1SD for Stim-Tg and u-hsTg measured was 1.0 ± 1.2 and 0.2 ± 0.1 μg/L, respectively. When adjusted for method of TSH stimulation, serial Stim-Tg measurements did not significantly change over time (all p = NS). The estimated changes in Stim-Tg per year for rhTSH, T4 withdrawal, and T3 withdrawal were 0.01, -0.08, and 0.04 μg/L, respectively. Upon exclusion of 73 patients with an initial undetectable Stim-Tg (n = 48), serial Stim-Tg measurements did not change significantly over time (all p = NS). For these patients, the estimated changes in Stim-Tg per year for rhTSH, T4 withdrawal, and T3 withdrawal were -0.09, -0.10, and 0.01 μg/L, respectively. Serial u-hsTg measurements did not significantly change over time after adjusting for TSH level (p = NS). The estimated change in u-hsTg per year was -0.003 μg/L. No patients had any clinical or imaging evidence of a recurrence during the duration of their follow-up. Among low/intermediate-risk PTC patients not treated with RAI, serial post-surgical Stim-Tg and u-hsTg measurements do not change significantly over a median follow-up of 6.5 years.

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.

Thyroglobulin antibody levels do not predict disease status in papillary thyroid cancer

BACKGROUND

Thyroglobulin antibodies (TgAb) are present in approximately 20% of patients with papillary thyroid cancer (PTC) and invalidate the serum thyroglobulin (Tg) level as a tumour marker. We examined whether trends in the TgAb level could serve as a surrogate marker of disease status in the surveillance of patients with PTC.

METHODS

All patients found to have a least one positive postoperative TgAb level (determined by the Beckman-Coulter Access Assay) after undergoing initial surgery for PTC from 2000 to 2010 at a single institution were included. Log-log transformation and linear regression were applied to longitudinal TgAb levels, yielding patient-specific regression coefficients that categorized as follows: highly negative, moderately negative and positive/no trend. The recurrence rate in each category was then assessed.

RESULTS

Ninety-three of 967 patients with PTC were included. Recurrent disease was detected in 19 patients (20%) after a mean follow-up time of 51 months. Regression coefficients in the highly negative and moderately negative groups were not different, and hence these groups were pooled. The proportion of recurrent cases in the negative trend group was similar to that in the positive/no trend group (19.7% vs 21.9%, NS). The mean regression coefficients were similar for recurrent and nonrecurrent cases within both the negative trend group (-0.89 vs -0.80, NS) and the positive/no trend group (0.08 vs 0.33, NS).

CONCLUSION

Trends in the TgAb level do not predict disease status in PTC in our experience. In the context of most commercially available TgAb assays, surveillance of TgAb-positive patients will hinge on high-quality imaging until a valid alternative serum marker to Tg is identified.

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.

Thyroid heterogeneity, as indicated by the CV of ultrasonographic intensities, correlates with anti-thyroid peroxidase antibodies in euthyroid Hashimoto's thyroiditis

Objective

To prospectively evaluate the heterogeneous appearance of the thyroid gland, reflecting inflammation and destruction in euthyroid Hashimoto’s thyroiditis (HT), we investigated the clinical utilities of the heterogeneity index (HI) [the coefficient of variance (CV) of the ultrasonographic (US) intensities], focusing on anti-thyroid peroxidase antibodies (TPO-Ab), which represent not only disease activity but also subsequent thyroid destruction of HT.

Methods

Forty-four consecutive patients with euthyroid HT [60.5 ± 2.7 years old (mean ± SE)] and 30 age-matched normal controls were studied. HI was calculated as the CV (SD/mean) of US intensities of either four points per lobe of the thyroid gland along a horizontal line at the depth of the right common carotid artery. Evaluation included serum levels of free thyroxine (FT4), free triiodothyronine (FT3), thyroid stimulating hormone (TSH), anti-thyroid peroxidase antibodies (TPO-Ab), anti-thyroglobulin antibodies (Tg-Ab), thyroglobulin and thyroid volume.

Results

While no differences were observed for TSH, FT₄ and FT_3, thyroglobulin and thyroid volume between the two groups, HI exhibited a tendency towards a significant difference (3.59 ± 0.20% in HT patients vs 3.23 ± 0.19% in normal group, p = 0.089). In HT patients, there was a significant and positive correlation of HI with TPO-Ab (r = 0.396, p = 0.034), whereas such a correlation was absent in normal controls. In both groups, there were no significant correlations of HI with Tg-Ab, FT₃, FT₄ or TSH.

Conclusions

This is the first report of the close relation between heterogeneity of US of the thyroid gland and TPO-Ab in euthyroid HT patients before the heterogeneity becomes distinguishable from normal thyroid glands. Furthermore, at this stage, subsequent thyroid destruction in HT might be already be predicted through the heterogeniety of the thyroid tissue.

Thyroglobulin autoantibodies in patients with papillary thyroid carcinoma: comparison of different assays and evaluation of causes of discrepancies

CONTEXT

Thyroglobulin autoantibodies (TgAb) have been proposed as a surrogate marker of thyroglobulin in the follow-up of differentiated thyroid carcinoma. Commercially available TgAb assays are often discordant. We investigated the causes of discrepancy.

DESIGN

TgAb were measured by three noncompetitive immunometric assays and three competitive RIA in 72 patients with papillary thyroid carcinoma and associated lymphocytic thyroiditis (PTC-T), 105 with papillary thyroid carcinoma and no lymphocytic thyroiditis (PTC), 160 with Hashimoto's thyroiditis, and in 150 normal subjects. The results of the six assays were correlated. TgAb epitope pattern, evaluated by inhibition of serum TgAb binding to thyroglobulin by TgAb-Fab regions A, B, C, and D, were compared in sera which were positive in all six assays (concordant sera) and positive in only one to five assays (discordant sera) were compared. TgAb International Reference Preparation (IRP) was measured in 2007 and 2009.

RESULTS

The correlations of the six assays ranged from -0.01 to 0.93 and were higher in PTC-T and Hashimoto's thyroiditis than in PTC and normal subjects. Two uncorrelated components, one including the three immunometric assays, the other the three RIA, explained 40 and 37% of the total variance of the results of the six assays. The levels of inhibition were higher in concordant sera than in discordant sera by TgAb-Fab region B (27.0%, 21.2-34.0 vs. 6.0%, and 2.7-12.7%) and region C (30.5%, 21.3-37.7 vs. 4.0%, and 1.0-6.5%); thus, the epitope pattern was more homogeneous in concordant sera than in discordant sera. TgAb IRP ranged from 157 to 1088 (expected 1000) IU/ml in 2009; results in 2007 were similar in all but two assays.

CONCLUSIONS

TgAb assays are highly discordant. Discrepancy is lower when comparing assays with similar methodology. Results of TgAb from PTC-T are more concordant than those from PTC because their epitope pattern is more restricted. The internal standardization of TgAb is generally, but not completely, satisfactory.

Can we interpret serum thyroglobulin results?

Thyroglobulin (Tg) is a tumour marker for differentiated thyroid cancer. Interpretation requires a knowledge of the current thyrotropin (TSH) concentration as secretion is TSH-dependent. While a raised serum Tg may be indicative of residual or recurrent thyroid cancer, trauma to the thyroid (e.g. surgical, biopsy or due to radioiodine treatment) also causes an increase. Tg may be measured when TSH is suppressed and also following recombinant TSH (rhTSH) stimulation. Interpretation of results in pregnancy and in children is discussed. Assay bias and interference by endogenous Tg antibodies (Abs) are the main confounders in the interpretation of results. Although there is an international standard for Tg, there are large differences in results and yet there are few assay-specific clinical decision limits. Patients should therefore be monitored with the same assay. Endogenous TgAbs may cause false-negative interference in immunometric assays and may cause false-positive results in radioimmunoassay. Although the measurement of TgAbs has been advocated for predicting interference, it is now clear that interference can still occur when TgAbs have not been detected, the effect being TgAb-assay-specific. Approaches to identifying those samples where there may be interference are discussed. The laboratory should have a protocol for the investigation of possible interferences and data on the bias of the Tg assay that they use. An appreciation of the clinical uses of the service is required as an understanding by endocrinologists, oncologists and endocrine surgeons of the analytical limitations of the service.