Biological variation of thyroid autoantibodies and thyroglobulin

Long-term stability of thyroid peroxidase antibody (anti-TPO) in serum in the Danish General Suburban Population Study

OBJECTIVES

We evaluated the long-term stability of thyroid peroxidase antibody (anti-TPO).

METHODS

In the Danish General Suburban Population Study (GESUS), serum samples were biobanked at -80 °C during 2010-2013. In a paired design with 70 subjects, we compared anti-TPO (30-198 U/mL) measured on fresh serum on Kryptor Classic in 2010-2011 (anti-TPOfresh) with anti-TPO remeasured on frozen serum (anti-TPOfrozen) on Kryptor Compact Plus in 2022. Both instruments used the same reagents and the anti-TPOn automated immunofluorescent assay, which was calibrated against the international standard NIBSC 66/387, based on the Time Resolved Amplified Cryptate Emission (TRACE) technology from BRAHMS. Values greater than 60 U/mL are regarded as positive in Denmark with this assay. Statistical comparisons included Bland-Altman, Passing-Bablok regression, and Kappa statistic.

RESULTS

The mean follow-up time was 11.9 years (SD: 0.43). For anti-TPOfrozen vs. anti-TPOfresh, the line of equality was within the confidence interval of the absolute mean difference [5.71 (-0.32; 11.7) U/mL] and the average percentage deviation [+2.22% (-3.89%; +8.34%)]. The average percentage deviation of 2.22% did not exceed analytical variability. Passing-Bablok regression revealed both a statistically significant systematic and proportional difference: Anti-TPOfrozen=-22.6 + 1.22*(anti-TPOfresh). Frozen samples were correctly classified as positive in 64/70 (91.4%; Kappa=71.8%).

CONCLUSIONS

Anti-TPO serum samples in the range 30-198 U/mL were stable after 12-years of storage at -80 °C with an estimated nonsignificant average percentage deviation of +2.22%. This comparison is based on Kryptor Classic and Kryptor Compact Plus, which used identical assays, reagents, and calibrator, but for which the agreement in the range 30-198 U/mL is unclarified.

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.

Longitudinal Tracking of Extractable Nuclear Antigen (ENA) Antibodies in a Quaternary Hospital Laboratory Cohort Reveals Dynamic Antibody Profiles

BACKGROUND

Antiextractable nuclear antigens (anti-ENAs) are regarded as diagnostic tests with no established value for serial monitoring. We therefore sought to establish the stability over time of anti-ENAs in a large diagnostic immunopathology laboratory.

METHODS

A retrospective review of all patients who had a serial anti-ENA ordered at the Westmead Hospital (Sydney, Australia) was performed over 24 months. Anti-ENA characterization was performed using line immunoassay, and historical data were available from 2013 onward. The earliest available densitometry readings were compared with the latest available to examine for a change in quantitation or qualitative (serostatus) result (from negative to positive, and vice versa). Medical records were examined for clinical correlations.

RESULTS

A total of 283 patients (24.1%) had serial testing of anti-ENA in the audit period, with each patient having an average of 3.9 ± 2.9 tests each. Most patients were diagnosed with systemic lupus erythematosus or primary Sjögren's syndrome. About 25% and 58% of patients had a qualitative and quantitative change, respectively, in at least 1 anti-ENA in the study period. Changes in anti-ENA levels correlated with erythrocyte sedimentation rate and disease activity. Increasing duration between serial tests increased the probability of observing a change in anti-ENA levels.

CONCLUSION

Certain anti-ENAs are dynamic autoantibodies that may have significance for monitoring disease activity. Laboratories may consider reporting quantitative results. Further disease- and autoantibody-specific studies are required to determine the clinical significance of changes in anti-ENAs.

Biological variation and analytical goals of four thyroid function biomarkers in healthy European volunteers

BACKGROUND

Interpretation of thyroid function tests by means of biological variation (BV) data is essential to identify significant changes between serial measurements at an individual level. Data on thyroid parameters in adults are limited.

OBJECTIVES

We aimed at determining the BV of four thyroid function test (thyroid-stimulating hormone (TSH), free thyroxin (FT4), free triiodothyronine (FT3) and thyroglobulin (Tg)) by applying recent recommendations to acquire BV data on a latest generation of immunoassay.

METHODS

Nineteen healthy volunteers (8 males and 11 females) were drawn every week during 5 consecutive weeks. Samples were analysed in duplicate on the Cobas 602 analyzer (Roche Diagnostics). After normality assessment, outlier exclusion and homogeneity of variance analysis, analytical variation (CV_A ), within-subject biological variation (CV_I ) and between-subject biological variation (CV_G ) were determined using nested ANOVA.

RESULTS

CV_A , CV_I and CV_G were 0.9%, 19.7% and 37.6% for TSH; 3.6%, 4.6% and 10.8% for FT4; 2.2%, 6.0% and 8.6% for FT3; and 0.9%, 15.4% and 84.9% for Tg. Index of individuality (II) for all parameters was between 0.2 and 0.7. The percentage above which the change between two measures is truly significant (reference change value) was 54.7% for TSH, 16.2% for FT4, 17.7% for FT3 and 42.8% for Tg.

CONCLUSION

Based on recent international recommendations, our study provides updated BV data for four thyroid function tests in European healthy volunteers. Reliable BV characteristics, and especially RCV, can facilitate the interpretation of consecutive thyroid function tests in an individual and therefore have the potential to efficiently support clinical decisions regarding thyroid diseases.

Precision of autoantibody assays in clinical diagnostic laboratories: What is the reality?

BACKGROUND

ISO 15189 accreditation remains a challenge for specialized laboratories. In the field of autoimmunity, beside the crucial problem of absence of standardization, laboratories have to manage the analytical performances of the large panel of assays in terms of sensitivity and specificity, but also on their measurement precision for which no reference values are available on biorepositories.

METHODS

As an initiative of the French EASI (European Autoimmunity Standardization Initiative) group, French clinical diagnostic laboratories were requested to participate in a survey aiming to analyze the coefficients of variation (CVs) of intra-run and inter-run variability obtained with assays quantifying 14 different autoantibodies. Two performance goals corresponding to the 90th percentile and the 50th percentile (lowest CV values reached by 90% and 50% of laboratories respectively) defined for three levels of concentration were calculated. The impact on the assay performances of the number of measurements, of the nature of the internal quality control (IQC) and the type of immunoassay, was also analyzed.

RESULTS

414 and 616 values of intra-run and inter-run CVs were collected, respectively. The 50th percentile performance goals were comprised between 1.0% and 8.9% for the intra-run CVs, and between 1.8% and 14.6% for the inter-run CVs. At 90th percentile, the performance goals were comprised between 3.2% and 13.5% for the intra-run CVs, and between 7.3% and 30.8% for the inter-run CVs. CVs calculated from 10 values were similar to those obtained from more values. Higher imprecision was observed when the antibody levels of the IQC was lower than 2 fold the positive threshold. Commercial IQCs gave lower CVs than IQCs derived from patient samples.

CONCLUSION

Our results allow proposing some acceptability limits for the precision performances of the autoantibody assays, compatible with the reality of life in diagnostic laboratories and clinical care.

Predicting response and toxicity to PD-1 inhibition using serum autoantibodies identified from immuno-mass spectrometry

Background: Validated biomarkers are needed to identify patients at increased risk of immune-related adverse events (irAEs) to immune checkpoint blockade (ICB). Antibodies directed against endogenous antigens can change after exposure to ICB. Methods: Patients with different solid tumors stratified into cohorts received pembrolizumab every 3 weeks in a Phase II trial (INSPIRE study). Blood samples were collected prior to first pembrolizumab exposure (baseline) and approximately 7 weeks (pre-cycle 3) into treatment. In a discovery analysis, autoantibody target immuno-mass spectrometry was performed in baseline and pre-cycle 3 pooled sera of 24 INSPIRE patients based on clinical benefit (CBR) and irAEs. Results: Thyroglobulin (Tg) and thyroid peroxidase (TPO) were identified as the candidate autoantibody targets. In the overall cohort of 78 patients, the frequency of CBR and irAEs from pembrolizumab was 31% and 24%, respectively. Patients with an anti-Tg titer increase ≥1.5x from baseline to pre-cycle 3 were more likely to have irAEs relative to patients without this increase in unadjusted, cohort adjusted, and multivariable models (OR=17.4, 95% CI 1.8-173.8, p=0.015). Similarly, patients with an anti-TPO titer ≥ 1.5x from baseline to pre-cycle 3 were more likely to have irAEs relative to patients without the increase in unadjusted and cohort adjusted (OR=6.1, 95% CI 1.1-32.7, p=0.035) models. Further, the cohort adjusted analysis showed patients with anti-Tg titer greater than median (10.0 IU/mL) at pre-cycle 3 were more likely to have irAEs (OR=4.7, 95% CI 1.2-17.8, p=0.024). Patients with pre-cycle 3 anti-TPO titers greater than median (10.0 IU/mL) had a significant difference in overall survival (23.8 vs 11.5 months; HR=1.8, 95% CI 1.0-3.2, p=0.05). Conclusions: Patient increase ≥1.5x of anti-Tg and anti-TPO titers from baseline to pre-cycle 3 were associated with irAEs from pembrolizumab, and patients with elevated pre-cycle 3 anti-TPO titers had an improvement in overall survival.

Concentration of fibrin monomer in pregnancy and during the postpartum period

Background

D-dimer increases during pregnancy and is problematic to use in the diagnosis of venous thromboembolism. Fibrin monomer represents an alternative biomarker for venous thromboembolism. However, to be useful in pregnancy, the fibrin monomer concentration should be stable throughout pregnancy and during postpartum.

Methods

To describe the course of fibrin monomer concentration during pregnancy and the postpartum period in healthy pregnant women and to compare their within-subject biological variation (CVI) with non-pregnant women. Blood samples were obtained every fourth week during pregnancy and three samples after delivery in 20 healthy women and every fourth week during a 40-week period in 19 healthy non-pregnant women. Fibrin monomer (STA Liatest FM, Stago) was analysed in duplicates for all samples. Concentrations of fibrin monomer in pregnant and non-pregnant women were compared and the CVI for fibrin monomer was calculated.

Results

The median fibrin monomer concentration in pregnant women was 6.2 mg/L (2.5 and 97.5 percentiles 3.7–10.8 mg/L) and in non-pregnant women 4.8 mg/L (3.6–8.2) ( P < 0.01). The fibrin monomer concentration was relatively stable during pregnancy, although a few unexplained high fibrin monomer concentrations were found during pregnancy/postpartum. Fibrin monomer CVI in pregnancy and postpartum was 20.6% (95% CI 18.3, 23.5) and in non-pregnant 16.1% (13.7, 18.9).

Conclusions

For clinical purposes, fibrin monomer concentration can be considered stable during pregnancy, although it is slightly higher than in non-pregnant women. Pregnant and non-pregnant women have the same CVI. The suitability of fibrin monomer in venous thromboembolism diagnosis in pregnant women should be validated in further studies.

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.

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.

Implications of thyroglobulin antibody positivity in patients with differentiated thyroid cancer: a clinical position statement

BACKGROUND

Even though the presence of antithyroglobulin antibodies (TgAbs) represents a significant problem in the follow-up of patients with differentiated thyroid cancer (DTC), the current guidelines on the management of DTC that have been published in recent years contain no text concerning the methods to be used for detecting such antibody-related interference in thyroglobulin (Tg) measurement or how to manage TgAb-positive patients in whom Tg cannot be used reliably as a tumor marker.

AIM

An international group of experts from the European Thyroid Association Cancer Research Network who are involved in the care of DTC patients met twice to form a consensus opinion on how to proceed with treatment and follow-up in TgAb-positive DTC patients based on the available evidence in the literature. Here we will report on the consensus opinions that were reached regarding technical and clinical issues.

RESULTS

This clinical opinion article provides an overview of the available evidence and the resulting consensus recommendations. The current literature does not provide sufficient data for giving evidence-based answers to many questions arising in the care of TgAb-positive DTC patients. Where insufficient evidence was available, a thorough discussion by a group of physician-scientists, all of whom have a distinguished track record in thyroid cancer care, was held to arrive at a consensus expert opinion. The questions and answers discussed were then summarized into an algorithm for the management of TgAb-positive patients.

CONCLUSION

We were able to define 26 consensus expert recommendations and a resulting algorithm for the care of TgAb-positive DTC patients.

A model for calculating the within-subject biological variation and likelihood ratios for analytes with a time-dependent change in concentrations; exemplified with the use of D-dimer in suspected venous thromboembolism in healthy pregnant women

BACKGROUND

Within-subject biological variation and reference change value (RCV) are difficult to calculate for an analyte with a changing concentration. The aim of this study was to develop a model to examine if it was possible to transform an analyte with a time-dependent change in concentration into a 'steady-state' situation by the use of 'multiples of the median' (MoM) and its natural logarithm (lnMoM). In addition, we wanted to extend the RCV concept, using likelihood and odds ratios, to calculate the post-test probabilities for disease. D-dimer in pregnancy is used as an example.

METHODS

Blood samples from 18 healthy pregnant and 18 healthy non-pregnant women were collected every fourth week. MoM of the D-dimer concentrations was calculated for each four-week interval to obtain a 'steady-state' situation for the D-dimer concentrations. The 'normalized' values were then transformed to the lnMoM to obtain a Gaussian distribution, used for the estimation of biological variation.

RESULTS

Median D-dimer concentrations increased six-fold during pregnancy. Within-subject variation (SD) of lnMoM D-dimer was 0.27 during pregnancy and 0.23 in non-pregnant women, with RCVs of 0.72 and 0.90, respectively.

CONCLUSIONS

By using the lnMoM model, an increasing concentration of an analyte can be transformed to a steady-state situation and the within-subject biological variation and its derived parameters can be calculated.

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.

Within-subject biological variation of glucose and HbA(1c) in healthy persons and in type 1 diabetes patients

BACKGROUND

Several articles describing within-subject biological variation of fasting glucose and HbA(1c) in healthy populations have been published, but information about biological variation of glucose and HbA(1c) in patients with type 1 diabetes is scarce. It is reasonable to assume that type 1 diabetics differ from their healthy counterparts in this matter. The aim of our study was to estimate the biological variation of glucose and HbA(1c) in healthy subjects and in patients with type 1 diabetes.

METHODS

Fifteen healthy individuals and 15 type 1 diabetes patients were included. Biological variations were calculated based on blood samples collected weekly for 10 consecutive weeks from the healthy and the eligible of the type 1 diabetes patients.

RESULTS

The within-subject variations of glucose were approximately 5% in healthy individuals and 30% in diabetes patients, and for HbA(1c) they were 1.2% in healthy individuals and 1.7% in diabetes patients.

CONCLUSIONS

In conclusion, we found a high within-subject biological variation of glucose in diabetes patients as expected compared to healthy individuals (30% vs. 5%). The short-term (2 months) within-subject biological variation of HbA(1c) did not differ significantly between well regulated type 1 diabetes patients and healthy individuals (1.7% vs. 1.2%).

A role for autoantibodies in enhancement of pro-inflammatory cytokine responses to a self-antigen, thyroid peroxidase

The role of thyroid peroxidase (TPO) antibodies (TPOAbs) in the pathogenesis of autoimmune thyroid disease is unclear. We selected sera with a high concentration of TPOAbs from eleven patients with Hashimoto's thyroiditis (HT), ten healthy monozygotic co-twins to HT patients, and twelve healthy individuals with no familiar disposition to AITD, and mixed each serum with normal mononuclear cells (MNCs). Following challenge with TPO, the MNCs' production of the pro-inflammatory cytokines TNF-alpha, IL-6 and IFN-gamma, and the anti-inflammatory cytokine IL-10, correlated with the TPOAb content of the serum present in the culture (p=0.0002-0.05). Enrichment of foetal calf serum-containing media with IgG with a high content of TPOAbs enhanced the TPO-elicited production of TNF-alpha, IL-6 and IFN-gamma by normal MNCs in a dose- and Fcgamma-receptor dependent manner (p<0.0002-0.05). The data indicate that TPO-induced release of pro-inflammatory cytokines from phagocytic cells and T-cell responses to TPO are promoted by TPOAbs.

Laboratory services for thyroglobulin and implications for monitoring of differentiated thyroid cancer

Serum thyroglobulin is used as a marker for monitoring differentiated thyroid cancer. There are a number of analytical challenges: the need for stability of the assay over decades, differences in assay bias, and interference in immunoassays by endogenous thyroglobulin antibodies. Improved precision at low analyte concentrations is desirable. Approaches to identifying assay interference are discussed. No single approach is likely to be successful on all occasions. Decision limits should be assay-specific, and clinicians should be aware of the limitations of current immunoassays.

Epitope recognition patterns of thyroid peroxidase autoantibodies in healthy individuals and patients with Hashimoto's thyroiditis*

OBJECTIVE

Thyroid peroxidase antibodies (TPOAb) are markers of autoimmune thyroid disease (AITD), including Hashimoto's thyroiditis (HT), but naturally occurring TPOAb are also detectable in healthy, euthyroid individuals. In AITD, circulating TPOAb react mainly with two immunodominant regions (IDR), IDR-A and IDR-B. The present study was undertaken in order to compare the epitope recognition pattern of TPOAb in HT patients and healthy subjects.

DESIGN

Sera from 21 out of 98 healthy controls were selected on the basis of high TPOAb values, required for determination of TPOAb recognition pattern; as were sera from 92 HT patients.

MEASUREMENTS

Measurement of IDR-reactivity was possible in 90 patients and 12 controls. IDR-A-, IDR-B- and non-IDR-A/non-IDR-B-Ab constituted 24 +/- 11%, 50 +/- 15% and 26 +/- 12%, respectively, in the patients. The distribution in the controls was distinctly different, only 12 +/- 13% being directed against IDR-A (P < 0.002) and 66 +/- 22% against IDR-B (P < 0.002). Half of the healthy individuals, vs. none of the HT patients, lacked IDR-A reactivity completely (P < 0.0001). In HT patients, IDR-B-Ab proportions increased slightly with increasing TPOAb levels (P < 0.05), while IDR-B-Ab of the controls showed a strong opposite trend (P < 0.0001). Accordingly, the proportion of non-A/non-B-Ab correlated with TPOAb levels in the healthy controls (P < 0.008), and an inverse correlation was seen in HT patients (P < 0.02).

CONCLUSION

The data suggest that TPOAb do not differ only in quantity between HT patients and healthy individuals, but may also follow distinct qualitative patterns. Larger studies are required to confirm this, and to determine whether the propensity to produce antibodies to certain TPO epitopes, for example, IDR-A, is of pathogenic relevance.