Performance of a third-generation TSH-receptor antibody in a UK clinic

Utility of TSH Receptor Antibodies in the Differential Diagnosis of Hyperthyroidism in Clinical Practice

Graves' disease (GD) is the most common cause of hyperthyroidism in iodine-sufficient areas. It is important to distinguish GD from other causes of hyperthyroidism for optimal management. Thyroid stimulating hormone receptor antibody (TRAb) test is a commonly used test for this purpose. However, the sensitivity for this test in routine clinical practice may be affected by various factors leading to fallacies in diagnosis.

Materials and Methods

A retrospective study was performed to assess the utility of an automated electrochemiluminescence TRAb immunoassay (Roche) in differentiating GD from non-Graves' disease (NGD) in routine clinical practice.

Results

In 227 subjects, 146 had GD and 81 had NGD. Total T3, Total T4, Free T4, and TRAb were significantly higher in people with GD in comparison to NGD. The area under the receiver operating characteristics (ROC) curve for the assay was 0.96 (95% CI: 0.926 to 0.984, P < 0.0001). The optimal threshold for the test derived from the ROC was 3.37 IU/L, which is more than the cut-off of 1.75 IU/L suggested by the manufacturer. The sensitivity/specificity of TRAb in the diagnosis of GD at presentation was 98.4%/62.9% at 1.75 IU/L and 91.2%/90.12% at 3.37 IU/L, respectively.

Conclusion

The TRAb test is a sensitive test to differentiate between subjects with GD and NGD presenting with hyperthyroidism. However, the cutoff (1.75 IU/L) as per the kit manufacturer may lead to a lower specificity for diagnosis. A modified cut-off of 3.37 IU/L should be considered for optimizing the diagnostic efficacy of the test.

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

BACKGROUND

Thyroid-stimulating hormone receptor (TSHR)-activating autoantibodies stimulate thyroid growth and hormone synthesis/secretion, causing hyperthyroidism of Graves' disease (GD). TRAb measurement helps diagnose GD and is an important first test in evaluating hyperthyroidism according to the recent American Thyroid Association guidelines. We compared the performance of the BRAHMS TRAK Kryptor (Thermo Scientific) and Roche cobas TRAb immunoassays for use in GD.

METHOD

Method comparison (n = 40) and clinical agreement were assessed between the Kryptor, cobas e411, and cobas e601. The analytical performance of Kryptor and cobas e411 were assessed for within- and between-day imprecision across 20 days, linearity, functional assay sensitivity (FAS), dilution recovery, and cut-off verification.

RESULTS

The Kryptor, e411, and e601 TRAb immunoassays correlated well (r > 0.95, overall percent agreement = 0.95, Cohen's kappa = 0.90). With a total allowable error of 20%, percent bias was within 13%, which was minimally negative at <20 IU/L, but highly positive (33%-34%) >20 IU/L. The Kryptor, but not e411, was linear across the claimed analytical measuring range (AMR). The claimed functional assay sensitivity (FAS), which was close to the clinical GD cut-off 1.8 IU/L, was verified for Kryptor and e411.

CONCLUSION

Overall, our evaluation demonstrates acceptable comparability between TRAb immunoassays with in-house imprecision up to 13% and 10% on Kryptor and e411, respectively. While Roche has preferable calibration frequency and on-board reagent stability, both platforms demonstrate acceptable imprecision using patient samples at their claimed FAS, which is important for GD diagnosis. Diluted results (using a negative patient pool as diluent) exhibits proportional positive bias on the Kryptor relative to the Roche methods.

Pitfalls in the assessment of gestational transient thyrotoxicosis

Gestational transient thyrotoxicosis (GTT) is associated with direct stimulation of the maternal thyroid gland by human chorionic gonadotropin (hCG). It is characterized by slightly higher thyroid hormone and lower thyroid-stimulating hormone (TSH) levels in early pregnancy and mild or no symptoms. While GTT must be distinguished from Graves' disease (GD), which is associated with maternal and fetal complications, treated GD and new-onset GD in pregnancy are occasionally challenging to distinguish. Evaluating serum hCG levels and TSH receptor antibody (TRAb) titers can help, but the results are not irrefutable due to pregnancy-related immunosuppression. Moreover, GTT can follow unusual clinical courses in relation to some pregnancy complications. Excessive hCG production can cause severe GTT symptoms in patients with hyperemesis gravidarum, trophoblastic disease, or multiple pregnancies. Thyrotoxicosis can emerge beyond the second trimester in patients with gestational diabetes mellitus and mirror syndrome, because of delayed elevations in the hCG levels. Detailed knowledge about GTT is necessary for correct diagnoses and its appropriate management. This review focuses on the diagnosis of GTT, and, particularly, its differentiation from GD, and unusual clinical conditions associated with GTT that require comprehensive management.

Comparison of Five TSH-Receptor Antibody Assays in Graves' disease: results from an observational pilot study

BACKGROUND

Early diagnosis and relapse prediction in Graves' disease influences treatment. We assessed the abilities of four TSH-receptor antibody tests [TRAb] and one cyclic adenosine monophosphate bioassay to predict relapse of Graves' disease.

METHODS

Observational study investigating patients presenting with Graves' disease at a Swiss hospital endocrine referral center or an endocrine outpatient clinic. Main outcomes were diagnosis and relapse of Graves' disease after stop of anti-thyroid drugs. We used Cox regression to study associations of TRAb levels with relapse risk and calculated c-statistics [AUC] to assess discrimination. Blood draws took place as close as possible to treatment initiation.

RESULTS

AUCs ranged from 0.90 (TSAb Biossay by RSR) to 0.97 (IMMULITE TSI by Siemens). Highest sensitivity (94.0%) was observed for IMMULITE TSI and RSR TRAb Fast, while the greatest specificity (97.9%) was found with the EliA anti-TSH-R (by Thermo Fisher). In Cox regression analysis comparing the highest versus the lower quartiles, the highest hazard ratio [HR] for relapse was found for BRAHMS TRAK (by Thermo Fisher) (2.98, 95% CI 1.13-7.84), IMMULITE TSI (2.40, 95% CI 0.91-6.35), EliA anti-TSH-R (2.05, 95% CI 0.82-5.10), RSR Fast TRAb (1.80, 95% CI 0.73-4.43), followed by RSR STIMULATION (1.18, 95% CI 0.46-2.99). Discrimination analyses showed respective AUCs of 0.68, 0.65, 0.64, 0.64, and 0.59.

CONCLUSION

The assays tested had good diagnostic power and relapse risk prediction with few differences among the new assays. Due to the small sample size and retrospective design with possible selection bias, our data need prospective validation.

Clinical diagnosis of Graves' or non-Graves' hyperthyroidism compared to TSH receptor antibody test

BACKGROUND

TSH receptor antibody (TRAb) is considered the gold standard diagnostic test for the autoimmunity of Graves' disease (GD), which is commonly diagnosed clinically.

AIM

To evaluate the true positive (sensitivity) and true negative (specificity) rates of clinical diagnosis of GD or non-GD hyperthyroidism compared to the TRAb test.

SETTING

University teaching hospital in North West England.

PARTICIPANTS

Patients in the Endocrinology service who had a TRAb measurement between December 2009 and October 2015.

METHODS

Electronic patient records were studied retrospectively for a pre-TRAb clinical diagnosis of GD or non-GD hyperthyroidism. We examined descriptive statistics and binary classification tests; Fisher exact test was used to analyse contingency tables.

RESULTS

We identified 316 patients with a mean age of 45 (range, 17-89) years; 247 (78%) were women. Compared to the TRAb result, clinical diagnosis had a sensitivity of 88%, specificity 66%, positive predictive value 72%, negative predictive value 84%, false negative rate 12%, false positive rate 34%, positive likelihood ratio 2.6 and negative likelihood ratio 0.2 (P < 0.0001).

CONCLUSIONS

Clinicians were liable to both over- and under-diagnose GD. The TRAb test can help reduce the number of incorrect or unknown diagnoses in the initial clinical assessment of patients presenting with hyperthyroidism.

Graves Disease in Central Ghana: Clinical Characteristics and Associated Factors

Background

Graves disease (GD) has increased in prevalence over the past decade in Africa. Despite this, the condition is not well described, especially in sub-Saharan Africa.

Objective

We have described the clinical characteristics and associated factors of GD in a cohort of patients attending a resource-limited setting tertiary hospital.

Methods

Patients were examined thoroughly and systematically tested for the degree of clinical and biochemical thyroid status. Thyroid volume, characteristics, and blood flow were assessed at presentation using ultrasonography. Factors associated with an inability to achieve clinical and biochemical thyroid remission were evaluated using multiple logistic regression analysis.

Results

Overall, 182 patients were studied, 152 (83.5%) were women with a female:male ratio of 5.1:1.0. The mean age at presentation was 39.9 ± 14.7 years with women significantly older than men. Thyroid-associated orbitopathy (TAO) was observed in 56% of the participants and pretibial myxoedema in 6%. About 84% of the participants were hyperthyroid at presentation, 9% were euthyroid, 4% were hypothyroid, and 3% had subclinical hyperthyroidism. Inability to achieve biochemical and clinical remission at 24 months was associated with increased thyroid volume (odds ratio [OR]: 2.35, 95% confidence interval [CI]: 1.85-2.52, P < .001), presence of TAO (OR: 2.15, 95% CI: 2.12-2.33, P < .001), increased FT3/FT4 ratio (OR: 1.33, 95% CI: 1.24-2.56, P = .004), and missed clinic appointment (OR: 5.2, 95% CI: 4.55-7.89, P < .001).

Conclusions

Graves disease among Ghanaians is associated with significant signs at presentation. Inability to achieve remission within the first 24 months is associated with increased thyroid volume, TAO, an increased FT3/FT4 ratio, as well as missed clinic appointment.

Persistent Graves’ hyperthyroidism despite rapid negative conversion of thyroid-stimulating hormone-binding inhibitory immunoglobulin assay results: a case report

Background

Case presentation

Conclusions

Thyroid antibody-negative euthyroid Graves' ophthalmopathy

TSH receptor antibodies (TRAbs) are the pathological hallmark of Graves' disease, present in nearly all patients with the disease. Euthyroid Graves' ophthalmopathy (EGO) is a well-recognized clinical entity, but its occurrence in patients with negative TRAbs is a potential source of diagnostic confusion. A 66-year-old female presented to our endocrinology clinic with right eye pain and diplopia in the absence of thyroid dysfunction. TRAbs were negative, as measured with a highly sensitive third(-)generation thyrotropin-binding inhibitory immunoglobulin (TBII) ELISA assay. CT and MRI scans of the orbit showed asymmetrical thickening of the inferior rectus muscles but no other inflammatory or malignant orbital pathology. Graves' ophthalmopathy (GO) was diagnosed on the basis of the clinical and radiological features, and she underwent surgical recession of the inferior rectus muscle with complete resolution of the diplopia and orbital pain. She remained euthyroid over the course of follow-up but ultimately developed overt clinical and biochemical hyperthyroidism, 24 months after the initial presentation. By this time, she had developed positive TRAb as well as thyroid peroxidase antibodies. She responded to treatment with thionamides and remains euthyroid. This case highlights the potential for negative thyroid-specific autoantibodies in the presentation of EGO and underscores the variable temporal relationship between the clinical expression of thyroid dysfunction and orbital disease in the natural evolution of Graves' disease.

LEARNING POINTS

Euthyroid Graves' ophthalmopathy can present initially with negative thyroid-specific autoantibodies.Patients with suggestive symptoms of ophthalmopathy should be carefully evaluated for GO with imaging studies even when thyroid function and autoantibodies are normal.Patients with EGO can develop thyroid dysfunction within 4 years of follow-up underpinning the need for long-term follow-up and continued patient and physician vigilance in patients who have been treated for EGO.

Methods for the investigation of thyroid function

In the developed world, all routine clinical laboratories should be able to perform tests for the assessment of the pituitary-thyroid axis. Testing strategies usually involve the measurement of thyroid-stimulating hormone (TSH), either alone or in combination with free thyroxine (FT4), which itself should also be measured when TSH is abnormal or if there is a suspicion of pituitary disease. Based on these findings, clinical history and medications such as amiodarone, free tri-iodothyronine (FT3), thyroid-binding globulin (TBG), and/or autoantibodies may then be measured. All these assays have their individual challenges. For example, sensitivity of a TSH assay is of crucial importance for improving distinction between eu- and hyperthyroidism. In the measurement of free hormones, there is the potential disturbance of the equilibrium between free and bound moieties by separating systems. There are a number of commercial diagnostic kits available for each of these tests. This chapter presents various representative assays and their principles. With the exception of FT4 determination by equilibrium dialysis, those that employ a 96-well plate format and use non-isotopic techniques have been described. Attention has been paid to limitations of the assays, standardization of assay kits, imprecision, recovery, detection limit, and ease of use. The assays described have been given as typical and reliable examples, but it is the responsibility of assayists to choose methods that are best suited to their needs.

Radioiodine therapy in benign thyroid diseases: effects, side effects, and factors affecting therapeutic outcome

Radioiodine ((131)I) therapy of benign thyroid diseases was introduced 70 yr ago, and the patients treated since then are probably numbered in the millions. Fifty to 90% of hyperthyroid patients are cured within 1 yr after (131)I therapy. With longer follow-up, permanent hypothyroidism seems inevitable in Graves' disease, whereas this risk is much lower when treating toxic nodular goiter. The side effect causing most concern is the potential induction of ophthalmopathy in predisposed individuals. The response to (131)I therapy is to some extent related to the radiation dose. However, calculation of an exact thyroid dose is error-prone due to imprecise measurement of the (131)I biokinetics, and the importance of internal dosimetric factors, such as the thyroid follicle size, is probably underestimated. Besides these obstacles, several potential confounders interfere with the efficacy of (131)I therapy, and they may even interact mutually and counteract each other. Numerous studies have evaluated the effect of (131)I therapy, but results have been conflicting due to differences in design, sample size, patient selection, and dose calculation. It seems clear that no single factor reliably predicts the outcome from (131)I therapy. The individual radiosensitivity, still poorly defined and impossible to quantify, may be a major determinant of the outcome from (131)I therapy. Above all, the impact of (131)I therapy relies on the iodine-concentrating ability of the thyroid gland. The thyroid (131)I uptake (or retention) can be stimulated in several ways, including dietary iodine restriction and use of lithium. In particular, recombinant human thyrotropin has gained interest because this compound significantly amplifies the effect of (131)I therapy in patients with nontoxic nodular goiter.

The role of thyrotrophin receptor antibody assays in graves' disease

Thyrotrophin receptor antibodies (TRAb) exist as stimulating or blocking antibodies in the serum (neutral TRAb have been identified recently). The clinical features of GD occur when stimulating TRAb predominate. But the relationship of TRAb to clinical phenotype and outcome is not clear when current assay methods are used. Therefore no consensus exists about its utility in diagnosing and predicting outcome in GD. The most commonly used TRAb assays, measure thyroid binding inhibiting immunoglobulins (TBII or “receptor assays”) and don't differentiate between stimulating and blocking antibodies. However, the more expensive, technically demanding and less freely available “biological assays” differentiate between them by their ability to stimulate cyclic AMP or failure to do so. Failure to differentiate between TRAb types and its heterogeneous molecular and functional properties has limited TBII use to GD diagnosis and differentiating from other forms of thyrotoxicosis. The current 2nd-3rd generation receptor assays are highly sensitive and specific when used for this purpose. TRAb assays should also be done in appropriate pregnant women. Current data do not support its use in outcome prediction as there is a significant variability of assay methodology, population characteristics and study design in published data, resulting in a lack of consensus.

Is the measurement of inferior thyroid artery blood flow velocity by color-flow Doppler ultrasonography useful for differential diagnosis between gestational transient thyrotoxicosis and Graves' disease? A prospective study

OBJECTIVE

To determine the role of peak systolic velocity, end-diastolic velocity and resistance indices of both the right and left inferior thyroid arteries measured by color-flow Doppler ultrasonography for a differential diagnosis between gestational transient thyrotoxicosis and Graves' disease during pregnancy.

METHODS

The right and left inferior thyroid artery-peak systolic velocity, end-diastolic velocity and resistance indices of 96 patients with thyrotoxicosis (41 with gestational transient thyrotoxicosis, 31 age-matched pregnant patients with Graves' disease and 24 age- and sex-matched non-pregnant patients with Graves' disease) and 25 age and sex-matched healthy euthyroid subjects were assessed with color-flow Doppler ultrasonography.

RESULTS

The right and left inferior thyroid artery-peak systolic and end-diastolic velocities in patients with gestational transient thyrotoxicosis were found to be significantly lower than those of pregnant patients with Graves' disease and higher than those of healthy euthyroid subjects. However, the right and left inferior thyroid artery peak systolic and end-diastolic velocities in pregnant patients with Graves' disease were significantly lower than those of non-pregnant patients with Graves' disease. The right and left inferior thyroid artery peak systolic and end-diastolic velocities were positively correlated with TSH-receptor antibody levels. We found an overlap between the inferior thyroid artery-blood flow velocities in a considerable number of patients with gestational transient thyrotoxicosis and pregnant patients with Graves' disease.

CONCLUSIONS

This study suggests that the measurement of inferior thyroid artery-blood flow velocities with color-flow Doppler ultrasonography does not have sufficient sensitivity and specificity to be recommended as an initial diagnostic test for a differential diagnosis between gestational transient thyrotoxicosis and Graves' disease during pregnancy.