Analytical performance evaluation of thyroid-stimulating hormone receptor antibody (TRAb) immunoassays

US-based, Prospective, Blinded Study of Thyrotropin Receptor Antibody in Autoimmune Thyroid Disease

CONTEXT

Bioassays provide information on the functionality of thyrotropin receptor antibodies (TSH-R-Ab) and thus may offer more clinical utility than binding assays.

OBJECTIVE

In this prospective, blinded, US-based study, the clinical performance of several TSH-R-Ab assays was compared.

SETTING

US endocrinology clinic.

SUBJECTS

One hundred sixty-two unselected, consecutive, well-documented patients with various thyroid diseases and healthy controls.

INTERVENTION(S)

Blinded TSH-R-Ab measurements.

MAIN OUTCOME MEASURE(S)

Sensitivity and specificity of 4 TSH-R-Ab assays.

RESULTS

The 4 TSH-R-Ab assays were negative in all 42 patients without autoimmune thyroid disease (AITD). In 104 patients with Graves' disease (GD), irrespective of the disease duration, TSH-R-Ab positivity was present in 65 (63%), 67 (65%), and 87 (84%) for the Cobas and Immulite binding assays and stimulatory TSH-R-Ab [thyroid-stimulating immunoglobin (TSI)] bioassay, respectively (TSI vs Immulite P < .0025, TSI vs Cobas P < .0009). Fifteen newly diagnosed GD patients were all positive in the TSI bioassay, but only 11 (73%) were positive in the Cobas and Immulite binding assays. Nine GD patients with biochemical subclinical hyperthyroidism were TSI-positive but Immulite- and Cobas-negative. Two GD patients were blocking TSH-R-Ab [thyroid-blocking immunoglobin (TBI)]-positive and TSI-negative, and the Immulite and Cobas were positive in both. Additional serum samples from AITD patients that consisted of 30 TBI-positive and 10 TSI-positive samples were blindly tested in the binding assays. Only 6 of the 10 TSI-positive samples were positive in both binding assays, and 30 and 28 of the TBI-positive samples were positive in the Cobas and Immulite assays, respectively.

CONCLUSION

Binding TSH-R-Ab assays are less sensitive than TSI bioassays and are not specific for stimulating antibodies. Measuring the function of TSH-R-Ab in a bioassay can provide useful information to clinicians.

Rituximab Treatment as Second-Line Therapy in Glucocorticoid Nonresponsive Graves' Orbitopathy: A Nonrandomized, Controlled, Interventional Study

OBJECTIVE

In moderate-to-severe Graves' orbitopathy, rituximab is recommended as second-line therapy in patients nonresponsive to intravenous glucocorticoids. We aimed to evaluate rituximab as early second-line therapy, as data are scarce and contradictory.

METHODS

In this nonrandomized, controlled, interventional study, patients with Graves' orbitopathy started on intravenous glucocorticoids. After 4 weeks, patients with < 2 points improvement in clinical activity score (CAS) were switched to rituximab [Non-Responders Rituximab (NR-RTX) group] and were compared to the remaining patients who continued with intravenous glucocorticoids for 12 weeks [Responders-Glucocorticoid (R-GC) group]. A retrospective group of non-responsive patients who were provided regular care with intravenous glucocorticoids for 12 weeks was used as control [Non-Responders-Regular Care group]. Background data and CAS were recorded for all groups at 0, 4, 12, 18, and 68 weeks. Quality of life (QoL) and safety data were collected from the NR-RTX and R-GC groups.

RESULTS

The NR-RTX group (n = 12) was similar to the others at baseline except for a 1-point lower median CAS compared to the NR-RC group (n = 12) (P = .03), and for having twice as many men compared to the R-GC group (n = 13) (P = .03). At 4 weeks, a linear mixed model indicated that the R-GC group had a 1.21-point (95% CI: -2.40 to -0.02) lower value for CAS compared to the NR-RTX group. CAS for all groups converged over time. Similar models for QoL revealed no treatment or time effects.

CONCLUSION

Switch to RTX early in the treatment course did not result in better CAS or QoL, compared to continuous intravenous glucocorticoids.

Establishment of Time-Resolved Fluorescence Immunoassay for Thyrotropin Receptor Antibodies and Clinical Application

Thyroid-stimulating hormone receptor antibody (TRAb) is a specific marker for Graves' disease (GD) and the measurement of which can improve the accuracy of GD diagnosis. Current detection methods utilize porcine-derived polyclonal-TRAb, which is unstable and is a source of significant inter-assay variability. This study aims to establish a time-resolved fluorescence immunoassay (TRFIA) method based on stable source of recombinant human TSHR and TRAb for the detection of serum TRAb. The neutralization inhibition method was used in this study. The specific binding of goat-anti-mouse IgG and chimeric construct Fc fragment human TSHR were immobilized on the microplate, and serum TRAb was detected by the competition between Eu3+-labeled human TRAb and the serum TRAb. The TRAb-TRFIA has a wide linear range (0.081-50 IU/L). The intra-assay precision was 2.17-5.41% (< 10%), and the inter-assay precision was 5.75-9.58% (< 15%). No cross-reactivity was observed between TRAb and recombinant human IgG1, IgG2, IgG3, or IgG4. The recovery rate was 106.37%. The TRAb-TRFIA method was significantly correlated with the Roche chemiluminescence method (R2 = 0.9130). TRFIA based on recombinant human TSHR and TRAb with high stability, strong specificity, high sensitivity and wide linear range was established for the detection of TRAb, which can be used for clinical detection.

Stability of Anti-thyroid Stimulating Hormone Receptor Antibody in Whole Blood and Serum: Caution Required for Reflective and Batch Testing

INTRODUCTION

Anti-thyroid stimulating hormone receptor antibody (TRAb) stability is stated as 7h at 20-25°C in the Roche Elecsys assay kit insert. The purpose of this study was to determine TRAb stability in whole blood and serum to assess the suitability of samples for reflective and weekly batch testing (with a single freeze-thaw cycle).

METHODS

In the first study, blood from n = 5 volunteers was used to assess: (1) stability in whole blood at room temperature up to 24h, and (2) stability in serum at 4-8°C up to 72h. In the second study, n = 21 patient samples were analysed in serum stored at 4-8°C for two and five days post-preliminary analysis.

RESULTS

There was a statistically significant decrease in TRAb concentration caused by the single freeze-thaw cycle of -8.9% ± 5.2% (p = 0.03). TRAb concentration decreased in whole blood between 0 and 24h by -16.5% ±9.2%, and declined in serum over time by -11.6% ±6.6% (at 12h). In the patient samples, serum TRAb concentration decreased over time by -4.6% ± 2.5% at day two and -6.5% ± 4.0% at day five.

CONCLUSION

TRAb concentration decreases over time in both whole blood at room temperature and serum samples stored at 4-8°C. A single freeze-thaw cycle also has a statistically significant effect on TRAb concentration.