Reference intervals for thyrotropin in an area of Northern Italy: the Pordenone thyroid study (TRIPP)

PURPOSE

Thyrotropin (TSH) is the most accurate marker of thyroid dysfunction in the absence of pituitary or hypothalamic disease. Studies on TSH reference intervals (RIs) showed wide inter-individual variability and prompted an intense debate about the best estimation of TSH RIs.

DESIGN

We performed a population study on TSH RIs, using current data stored in the laboratory information system (LIS), at the Hospital Department of Laboratory Medicine, Pordenone (Italy), historically an area of mild-moderate iodine deficiency with a relatively high goiter prevalence.

METHODS

136,650 individuals constituted the final sample. A TSH immunoassay was performed on fasting serum samples with the Dimension Vista 1500 analyzer (Siemens Healthineers). We adopted the Kairisto's procedure to analyze TSH data downloaded by the LIS, applying the indirect strategy for deriving RIs.

RESULTS

TSH RIs of the entire population were 0.32-3.36 mIU/L with a distribution skewed towards higher values. RIs were 0.26-3.61 mIU/L for females, and 0.32-3.01 mIU/L for males. Unlike other studies, TSH median levels progressively decreased from 0-4 to 85-104 years in the overall population, both in male and in female subgroups, showing an inverse correlation between TSH and age in all groups.

CONCLUSIONS

This study is the first to analyze a high percentage (40%) of individuals from an ethnically homogenous Caucasian population. The results obtained emphasize the opportunity to define the TSH RIs according to age, gender and race, in addition to assay methods, and provide further insight about the possible role of iodine status.

Definition of the upper reference limit for thyroglobulin antibodies according to the National Academy of Clinical Biochemistry guidelines: comparison of eleven different automated methods

Purpose

In the last two decades, thyroglobulin autoantibodies (TgAb) measurement has progressively switched from marker of thyroid autoimmunity to test associated with thyroglobulin (Tg) to verify the presence or absence of TgAb interference in the follow-up of patients with differentiated thyroid cancer. Of note, TgAb measurement is cumbersome: despite standardization against the International Reference Preparation MRC 65/93, several studies demonstrated high inter-method variability and wide variation in limits of detection and in reference intervals. Taking into account the above considerations, the main aim of the present study was the determination of TgAb upper reference limit (URL), according to the National Academy of Clinical Biochemistry guidelines, through the comparison of eleven commercial automated immunoassay platforms.

Methods

The sera of 120 healthy males, selected from a population survey in the province of Verona, Italy, were tested for TgAb concentration using eleven IMA applied on as many automated analyzers: AIA-2000 (AIA) and AIA-CL2400 (CL2), Tosoh Bioscience; Architect (ARC), Abbott Diagnostics; Advia Centaur XP (CEN) and Immulite 2000 XPi (IMM), Siemens Healthineers; Cobas 6000 (COB), Roche Diagnostics; Kryptor (KRY), Thermo Fisher Scientific BRAHMS, Liaison XL (LIA), Diasorin; Lumipulse G (LUM), Fujirebio; Maglumi 2000 Plus (MAG), Snibe and Phadia 250 (PHA), Phadia AB, Thermo Fisher Scientific. All assays were performed according to manufacturers’ instructions in six different laboratories in Friuli-Venezia Giulia and Veneto regions of Italy [Lab 1 (AIA), Lab 2 (CL2), Lab 3 (ARC, COB and LUM), Lab 4 (CEN, IMM, KRY and MAG), Lab 5 (LIA) and Lab 6 (PHA)]. Since TgAb values were not normally distributed, the experimental URL (e-URL) was established at 97.5 percentile according to the non-parametric method.

Results

TgAb e-URLs showed a significant inter-method variability. Considering the same method, e-URL was much lower than that suggested by manufacturers (m-URL), except for ARC and MAG. Correlation and linear regression were unsatisfactory. Consequently, the agreement between methods was poor, with significant bias in Bland–Altman plot.

Conclusions

Despite the efforts for harmonization, TgAb methods cannot be used interchangeably. Therefore, additional effort is required to improve analytical performance taking into consideration approved protocols and guidelines. Moreover, TgAb URL should be used with caution in the management of differentiated thyroid carcinoma patients since the presence and/or the degree of TgAb interference in Tg measurement has not yet been well defined.

The upper reference limit for thyroid peroxidase autoantibodies is method-dependent: A collaborative study with biomedical industries

BACKGROUND

The determination of the upper reference limit (URL) for thyroid peroxidase autoantibodies (TPOAbs) is a contentious issue, because of the difficulty in defining the reference population. The aim of this study was to establish the URL (eURL) for TPOAbs, according to the National Academy of Clinical Biochemistry (NACB) guidelines and to compare them with those obtained in a female counterpart, by the use of six commercial automated platforms.

METHODS

120 healthy males and 120 healthy females with NACB-required characteristics (<30years, TSH between 0.5 and 2.0mIU/L, normal thyroid ultrasound, without personal/family history of thyroid and non-thyroid autoimmune diseases) were studied. Sera were analyzed for TPOAbs concentration using six immunoassay methods applied in automated analyzers: Advia Centaur XP (CEN), Siemens Healthcare Diagnostics; Maglumi 2000 Plus, Shenzen New Industries Biomedical Engineering; Architect ci4100, Abbott; Cobas e411 (COB) Roche Diagnostics; Unicel DxI (UNI) and Lumipulse G1200, Fujirebio.

RESULTS

Within each method, TPOAbs values had a high degree of dispersion and the eURLs were lower than those stated by the manufacturer. A statistically significant difference (p<0.05) between medians of males and females was observed only for COB and for UNI. However, the comparison of the male and female proportions positive for TPOAbs using the eURL of the counterpart, showed the lack of clinical significance of the above differences (Chi-square test, p>0.05).

CONCLUSIONS

Despite the analytical harmonization, the wide dispersion of the results and the differences of the eURLs between methods suggest the need of further studies focusing on TPO antigen preparations as the possible source of variability between different assays. In addition, the lack of clinical significant difference between males and females, in terms of TPOAb eURLs, confirms the suitability of the NACB recommendations.

Establishment of the upper reference limit for thyroid peroxidase autoantibodies according to the guidelines proposed by the National Academy of Clinical Biochemistry: comparison of five different automated methods

Aim of the study

The estimation of the upper reference limit (URL) for autoantibodies against thyroid peroxidase (TPOAbs) is a controversial issue, because of an uncertainty associated with the criteria used to correctly define the reference population. In addition, the URL of TPOAbs is method-dependent and often arbitrarily established in current laboratory practice. The aim of this study was to determine the reference limits of TPOAbs in a male sample according to the National Academy of Clinical Biochemistry (NACB) guidelines, and to compare them with those obtained in a female group, for five third-generation commercial-automated immunoassay (IMA) platforms.

Methods

120 healthy males and 120 healthy females with NACB-required characteristics (younger than 30 years, TSH between 0.5 and 2.0 mIU/L, normal thyroid ultrasound, absence of thyroid disease and absence of other autoimmune diseases) were studied. Sera were analyzed for TPOAbs concentration using five IMA methods applied in automated analyzers: Immulite 2000 XPi (IMM); Maglumi 2000 Plus (MAG); Kryptor Compact Plus (KRY); Phadia 250 (PHA) and Liaison XL (LIA).

Results

A statistically significant difference (p < 0.05) between medians in male and female groups was observed for PHA (2.6 and 3.1 IU/mL, respectively) but not for the other four methods. Scatter plots of TPOAbs values revealed a wide dispersion with very different coefficients of variation between the five methods, varying from 48.6 % for KRY in females to 126.3 % for MAG in females. The URLs differed in males and females according to the method: 28.7 and 29.0 IU/mL for IMM, 24.6 and 25.4 IU/mL for MAG, 6.4 and 6.9 IU/mL for KRY, 8.3 and 10.0 IU/mL for PHA and 14.2 and 17.9 IU/mL for LIA, respectively. Such URLs were lower than those stated by the manufacturers except for LIA in females. The difference between URLs ranged from a minimum of 11.3 % (LIA in males) to a maximum of 66.8 % (PHA in males).

Conclusions

Differences in URLs could result from the different coating preparations of the TPO antigen (purified native or recombinant) on solid phase, which affect the proper exposure of the immunodominant epitopes recognized by the polyclonal antibodies present in serum of patients with autoimmune thyroid disease (AITD). Based on these findings, we suggest to overcome the proposal of the NACB guidelines which recommend to involve a single group of young male subjects, and propose, instead, to utilize two distinct groups: one of males and one of females. This new proposal removes the apparent contrast of an all-male reference group for a disease (such as AITD) that affects mainly females. However, in spite of the harmonization among methods provided by the use of an international standard preparation, the wide dispersion of quantitative results still observed in this study suggests the need for further efforts to better understand the cause of these discrepancies, focusing on TPO antigen preparations as the possible source of variability among different assays.

Is vitamin D a player or not in the pathophysiology of autoimmune thyroid diseases?

1,25-Dihydroxyvitamin D is a steroid hormone derived from vitamin D, playing an important role in maintaining an adequate serum level of calcium and phosphorus. It is now clear that vitamin D exerts an endocrine action on the cells of the immune system, generating anti-inflammatory and immunoregulatory effects. The mechanisms underlying the role of vitamin D in autoimmunity are not completely understood. Lower vitamin D levels have been found in several autoimmune diseases, such as rheumatoid arthritis, systemic lupus erythematosus, systemic sclerosis, type 1 diabetes mellitus, multiple sclerosis, inflammatory bowel diseases, autoimmune thyroid diseases (i.e. Hashimoto's thyroiditis and Graves' disease) and autoimmune gastritis. Several genetic studies have demonstrated an association between thyroid autoimmunity susceptibility and gene polymorphisms of vitamin D receptor, vitamin D binding protein, 1-alpha-hydroxylase and 25-hydroxylase. Of note, some papers do not confirm this connection. With regard to the role of vitamin D in autoimmune thyroid diseases, available data remain controversial. Only few reports have analyzed the supposed association between autoimmune thyroid diseases and vitamin D concentration with inconclusive results. In our experience, low serum levels of vitamin D do not correlate either with Hashimoto's thyroiditis or with Graves' disease. The inability to achieve an unambiguous conclusion is in part due to the limitations in study design. In fact, most of the studies are cross-sectional surveys with a small number of subjects. In addition, the heterogeneity of the study population, seasonal variation of blood sampling, inter-method analytical variability of vitamin D assays and different definitions of vitamin D deficiency/insufficiency contribute to contradicting results. Therefore, further randomized, controlled, prospective trials are needed in order to demonstrate the causality of vitD in AITD and consequently the role of vitamin D supplementation in prevention or improvement of AITD, providing also information on the best formulation, dose and timing of supplementation.

Requirements for reproducibility, trueness and error of measurement in internal quality control schemes

Among the various models proposed to meet requirements for metrological performance in clinical laboratory measurements, that most widely used is intra- and inter-biological variation. However, this model has weaknesses: a) in some cases, intra-individual biological variation is so small that requirements based on such data may not be met by routine methods; b) there is great variation among the intra- and inter-individual biological variations themselves. We therefore propose integration between "state-of-the-art" methods to minimize imprecision, and also suggest that requirements calculated on the basis of biological variations should be used in setting requirements for minimizing imprecision. Furthermore, we describe a new scale for setting requirements from biological variation data and suggest that systematic error should be corrected whenever it is statistically significant.

Immunoturbidimetric assay of glycated hemoglobin

We investigated the performances of HbA1c determination by a latex enhanced turbidimetric immunoassay using the specific monoclonal antibodies (Unimate, Roche) against the beta-N-terminal fragments. The coefficients of variation ranges from 1.7 to 3.8% within assay (n = 30) and from 3.9 to 4.9% between assay (n = 20). The assay was linear from 2.5 to 14.9% of HbA1c. No interferences was found from fetal, carbamylated, or variant (S) hemoglobins and from labile Schiff adduct with glucose. The following relationship was derived from fresh sample comparison between HPLC (Diamat-BioRad) (x) and immunoassay (y) method: y = 0.971 x + 0.87%, r=0.98, n = 115. The immunoassay provides a highly precise and specific method for HbA1c.

Altered lipid peroxidation/glutathione ratio in experimental extrahepatic cholestasis

1. Lipid peroxidation can occur in the presence of a cellular antioxidant-oxidant imbalance, but the role of lipid peroxides in cholestasis is not well understood. 2. This study was undertaken in order to: (i) evaluate the behaviour of a product of lipid peroxidation (thiobarbituric acid-reactive species), and of an important antioxidant tripeptide, reduced glutathione, in the course of experimental extrahepatic cholestasis; and (ii) ascertain whether there was a link between this aspect and the alterations in liver morphology. 3. Forty-five male Sprague-Dawley rats (250-300 g) were double bile duct ligated and followed from 1 to 28 days. At the end of each experimental period, blood and liver samples were collected for thiobarbituric acid-reactive species and glutathione determinations. 4. Bile duct ligated rats showed a marked increase in liver weight which was related to cholestasis duration and to some anatomical alterations such as bile duct proliferation and dilation and liver fibrosis (periportal, perivenular, perineoductular and parenchymal). 5. An increase in serum lipid peroxidation was also observed but this was not linked to hepatic thiobarbituric acid-reactive species. Erythrocyte and hepatic glutathione decreased in relation to cholestasis duration. Serum lipid peroxides and erythrocyte glutathione were correlated with liver cell necrosis. 6. In conclusion, experimental extrahepatic cholestasis determines bile duct proliferation and fibrosis, the degree of which is directly related to the duration of cholestasis itself and to liver cell necrotic phenomena.(ABSTRACT TRUNCATED AT 250 WORDS)