Implementing reference systems for thyroid function tests - A collaborative effort

Challenges in harmonizing immunoassays: The use of the Bland-Altman based harmonization algorithm

BACKGROUND

In this study, we compared the recently proposed Bland-Altman plot-based harmonization algorithm (BA-BHA) with the weighted Deming regression-based harmonization algorithm (WD-BHA) taken as an example in ISO 21151:2020, aiming to evaluate the effectiveness of BA-BHA and discuss the applicability of these two different harmonization algorithms.

METHODS

BA-BHA and WD-BHA were applied to 19 measurands on LiCA medical devices, Chemclin Diagnostics Co., Ltd. A panel of 80 patient sera were collected for each measurand and the effectiveness of BA-BHA and the applicability of the two different harmonization algorithms were specified according to the Bland-Altman (B-A) plot, curve estimation and the Passing-Bablok regression.

RESULTS

After harmonized with BA-BHA, the mean of the B-A plot for each measurand was close to zero, and the limits of agreement (LoAs) met the quality requirements. The distribution of the variations in the B-A plot was demonstrated approximately symmetric over the measuring interval. Furthermore, "0" was included in the 95% confidence interval of the intercept and "1" was included in the 95% confidence interval of the slope for the Passing-Bablok regression, indicating acceptable harmonization effects for all 19 measurands. In contrast, acceptable harmonization effects were achieved in only some of the 19 measurands.

CONCLUSION

Acceptable harmonization effects can be achieved for various measurands by BA-BHA because both the mean and the distribution of percent differences in the B-A plot can be adjusted, which demonstrating BA-BHA with a more extensive applicability compared to WD-BHA.

Evaluation of the Current State of Thyroid Hormone Testing in Human Serum-Results of the Free Thyroxine and Thyrotropin Interlaboratory Comparison Study

Background: Performance of thyroid function assays can vary significantly. To address this issue, the Centers for Disease Control and Prevention (CDC) Clinical Standardization Programs conducted an interlaboratory comparison of free thyroxine (fT4) immunoassays (IAs) and laboratory-developed tests (LDTs). This assessment aimed to determine the current performance characteristics of these assays as a first step toward measurement standardization. Thyrotropin (TSH) IAs were also evaluated. Methods: Assays measured 41 blinded individual-donor sera, including a sample from a pregnant woman (for fT4 analysis only) and three serum pools, with 11.3-32.1 pmol/L (0.881-2.49 ng/dL) fT4 and 0.337-21.6 mIU/L TSH in duplicate over 2 days. Passing-Bablok regression analysis performed pre-recalibration compared assays performance to the CDC fT4 reference measurement procedure (RMP) or TSH all-lab mean (ALM). Additionally, the impact of linear regression-based recalibration of assays to the CDC fT4 RMP or TSH ALM was estimated. Inter-assay agreement of sample classification according to the assay-specific reference interval (RI) was assessed pre- and post-recalibration. Results: A total of 21 fT4 and 17 TSH assays participated. Pre-recalibration, median biases of TSH measurements to the ALM were -1.2% [confidence interval or CI -1.8% to -0.4%], and good classification agreement among TSH assays was observed. fT4 assays all showed a negative median bias to the RMP, with higher bias among IAs (median: -20.3%, CI [-21.5% to -19.4%]) than LDTs (median: -4.5%, [CI -6.1% to -3.2%]). Of the individual-donor sera, only 21 out of 40 samples were classified uniformly by all fT4 assays, indicating poor inter-assay agreement. Post-recalibration, agreement improved to 33 out of 40 individual-donor sera correctly classified by all tested IAs and LDTs. Similar improvement in post-recalibration median percent bias was observed for fT4 IAs (median: -0.2, [CI -1.2% to 0.6%]) and LDTs (median: -0.3%, [CI -2.5% to 1.4%]). Conclusions: The comparison among fT4 assays emphasizes the need for measurement standardization to improve accuracy and comparability. This and previous studies demonstrate the possibility to develop common fT4 RIs via standardization, enabling the use of evidence-based clinical guidelines universally in patient care. Recalibration can effectively address high variability in fT4 assays, ensuring consistent diagnostic classification.

Agreement between routinely used immunoassays for thyroid function testing in non-pregnant and pregnant adults

OBJECTIVE

Thyroid function tests are common biochemical analyses, and agreement between the routinely used immunoassays is important for diagnosis and monitoring of thyroid disease. Efforts are continuously made to align the biochemical assays, and we aimed to evaluate the agreement between immunoassays used in a clinical laboratory setting among non-pregnant and pregnant adults.

DESIGN

Cross-sectional study.

PARTICIPANTS

Serum samples were obtained from 192 blood donors (non-pregnant adults) and from 86 pregnant women in the North Denmark Region with no known thyroid disease.

MEASUREMENTS

Each sample was used for measurement of thyroid-stimulating hormone (TSH) with the routinely used automatic immunoassays in the regional Departments of Clinical Biochemistry (Alinity, Abbott Laboratories, Cobas, Roche Diagnostics, and Atellica, Siemens Healthineers) and reported as the median with 95% confidence interval (95% CI).

RESULTS

In nonpregnant adults, the level of TSH was higher with Cobas and Atellica than with Alinity as reflected by median (Alinity: 1.39 mIU/L (95% CI: 1.30-1.51 mIU/L); Cobas: 1.57 mIU/L (95% CI: 1.48-1.75 mIU/L); Atellica: 1.74 mIU/L (95% CI: 1.61-1.83 mIU/L)). Similarly, a trend was seen towards higher median TSH with Cobas than with Alinity among pregnant women (Alinity: 1.90 mIU/L (95% CI: 1.37-2.82 mIU/L); Cobas: 2.33 mIU/L (95% CI: 1.69-3.62 mIU/L)).

CONCLUSION

Results of thyroid function tests obtained with different immunoassays were not interchangeable when evaluated among pregnant and non-pregnant adults. The distinct differences are relevant for clinical decision making and emphasize the necessity of clinical laboratory information when different assays are used for diagnosis and monitoring of patients with thyroid disease.

A mathematical algorithm to harmonize measurements for thyroid-stimulating hormone between instruments

BACKGROUND

Thyroid-stimulating hormone (TSH) is measured differently between diagnostic units using different devices, which makes cross-comparisons challenging. Here, we have developed a mathematical algorithm to harmonize TSH measurements between 2 instruments, the Abbott ISR2000 and the Siemens ADVIA Centaur XP.

METHODS

Applying the principle of the maximum allowable error between the standard curve and real signal values, the minimum number of comparison samples required for TSH hormone detection was calculated for both instruments. Next, a mathematical algorithm describing the relationship between TSH standard curves from both instruments was established. The algorithm was then tested on sample measurements from both instruments, with signals transformed to Siemens ADVIA Centuar XP-type data. Finally, test results were assessed where the relative error was 

RESULTS

Before conversion, the mean percentage error between the TSH results of samples measured on both instruments was 23.20% (>1/2 TEa). After algorithmic transformation, the average percentage error was reduced to 7.93% (<1/2 TEa).

CONCLUSIONS

Our algorithm enables TSH measurements across different instruments to be comparable, and provides a method to harmonize TSH data between laboratories that utilize different instrumentation.

Collapse

Key Words

• Comparability
• Conversion
• Determination
• Mathematical algorithm
• Thyroid-stimulating hormone (TSH)

Collapse

MESH Headings

• Humans
• Thyrotropin
• Algorithms

Collapse

Grants Collapse

Affiliation(s)

Xin Zhou Department of Laboratory Medicine, West China Hospital of Sichuan University, Chengdu 610041, China; Jintang First People's Hospital, Chengdu 610400, China
Zaishuan Liu Department of Laboratory Medicine, West China Hospital of Sichuan University, Chengdu 610041, China
Yining Ma College of Mathematics of Sichuan University, Chengdu 610065, China
Chongwei Zhang Department of Laboratory Medicine, West China Hospital of Sichuan University, Chengdu 610041, China
Yongkang Wu Department of Laboratory Medicine, West China Hospital of Sichuan University, Chengdu 610041, China; Jintang First People's Hospital, Chengdu 610400, China.

Collapse

Practical considerations for accurate determination of free thyroxine by equilibrium dialysis

Background

Free thyroxine (FT4) measurement is one of the most requested tests in patient care for diagnosing and treating thyroid-related illnesses. Equilibrium dialysis (ED) is considered the "gold standard" for FT4 measurement; however, several factors have a profound effect on the reliability of FT4 assays and require special consideration.

Methods

In the current study, we focused on evaluating critical factors that could contribute to reporting errors, such as adsorption of thyroxine (T4) to labware surfaces, stability of serum samples, stock solutions, and calibrator storage conditions, as well as the solvents used to prepare T4 solutions.

Results

The adsorption of T4 in ethanolic solutions and dialysates to labware surfaces can be reduced with the careful selection of pipette tips, test tubes, and 96-well plates. Adding pH modifiers to neat T4 solutions can improve its stability. FT4 in serum samples remains stable after exposure to four freeze-thaw cycles, 5 °C for 18-20 h, or -70 °C for a minimum of three years.

Conclusion

The presented study has demonstrated that the loss of analyte due to pre-analytical and analytical factors during operation of the FT4 reference measurement procedure (RMP) can be minimized by careful selection of all labware for sample preparation. It was found that the accuracy and imprecision of FT4 assays can be influenced by different types of dialysis devices, but acceptable alternatives to ED membranes were identified. This study demonstrates approaches to establish a FT4 method that is independent from specific suppliers and addresses critical pre-analytical and analytical factors important for FT4 measurements.

Development of an equilibrium dialysis ID-UPLC-MS/MS candidate reference measurement procedure for free thyroxine in human serum

BACKGROUND

Accurate and reliable measurement of human serum free thyroxine (FT4) is critical for the diagnosis and treatment of thyroid diseases. However, concerns have been raised regarding the performance of FT4 measurements in patient care. Centers for Disease Control and Prevention Clinical Standardization Programs (CDC-CSP) address these concerns by creating a FT4 standardization program to standardize FT4 measurements. The study aims to develop a highly accurate and precise candidate Reference Measurement Procedure (cRMP), as one key component of CDC-CSP, for standardization of FT4 measurements.

METHODS

Serum FT4 was separated from protein-bound thyroxine with equilibrium dialysis (ED) following the recommended conditions in the Clinical and Laboratory Standards Institute C45-A guideline and the published RMP [20,21,23]. FT4 in dialysate was directly quantified with liquid chromatography-tandem mass spectrometry (LC-MS/MS) without derivatization. Gravimetric measurements of specimens and calibrator solutions, calibrator bracketing, isotope dilution, enhanced chromatographic resolution, and T4 specific mass transitions were used to ensure the accuracy, precision, and specificity of the cRMP.

RESULTS

The described cRMP agreed well with the established RMP and two other cRMPs in an interlaboratory comparison study. The mean biases of each method to the overall laboratory mean were within ±2.5%. The intra-day, inter-day, and total imprecision for the cRMP were within 4.4%. The limit of detection was 0.90 pmol/L, which was sufficiently sensitive to determine FT4 for patients with hypothyroidism. The structural analogs of T4 and endogenous components in dialysate did not interfere with the measurements.

CONCLUSION

Our ED-LC-MS/MS cRMP provides high accuracy, precision, specificity, and sensitivity for FT4 measurement. The cRMP can serve as a higher-order standard for establishing measurement traceability and provide an accuracy base for the standardization of FT4 assays.

Identifying elevated plasma free triiodothyronine levels: age-adapted reference intervals for pediatrics

OBJECTIVES

Elevated free T3 (FT3) is an important feature for the early diagnosis of several diseases among which Grave's disease or Allan-Hernon-Dudley syndrome. However, there is a lack of age-adapted reference intervals for plasma thyroid hormones in children. We conducted a study to define reference values of peripheral FT3 in children using a commonly used automated immunoassay.

METHODS

All thyroid function test (TFT) results from our lab collected during 9 months were extracted anonymously, and reference intervals establishment followed recommendations validated by International Federation of Clinical Chemistry (IFCC).

RESULTS

We defined five reference intervals covering the whole pediatric period. Overall, 26.1% of peripheral FT3 measured in children with normal TSH are out of the adult reference range, and 22.2% are upper it leading to misinterpretation. In a 9-month old patient with severe neurodevelopmental disorders, a pathological elevated FT3 has been securely interpreted using the newly established interval.

CONCLUSIONS

The study highlights the poor relevance of adult intervals in pediatric cares, as it confirms that plasmatic FT3 is higher during the whole pediatric period. This work reports useful age-adapted reference intervals for free T3 in pediatrics using a widely used electrochemiluminescent Immunoassay (ECLIA) kit.

Free thyroxine measurement in clinical practice: how to optimize indications, analytical procedures, and interpretation criteria while waiting for global standardization

Thyroid dysfunctions are among the most common endocrine disorders and accurate biochemical testing is needed to confirm or rule out a diagnosis. Notably, true hyperthyroidism and hypothyroidism in the setting of a normal thyroid-stimulating hormone level are highly unlikely, making the assessment of free thyroxine (FT4) inappropriate in most new cases. However, FT4 measurement is integral in both the diagnosis and management of relevant central dysfunctions (central hypothyroidism and central hyperthyroidism) as well as for monitoring therapy in hyperthyroid patients treated with anti-thyroid drugs or radioiodine. In such settings, accurate FT4 quantification is required. Global standardization will improve the comparability of the results across laboratories and allow the development of common clinical decision limits in evidence-based guidelines. The International Federation of Clinical Chemistry and Laboratory Medicine Committee for Standardization of Thyroid Function Tests has undertaken FT4 immunoassay method comparison and recalibration studies and developed a reference measurement procedure that is currently being validated. However, technical and implementation challenges, including the establishment of different clinical decision limits for distinct patient groups, still remain. Accordingly, different assays and reference values cannot be interchanged. Two-way communication between the laboratory and clinical specialists is pivotal to properly select a reliable FT4 assay, establish reference intervals, investigate discordant results, and monitor the analytical and clinical performance of the method over time.

How to approach clinically discordant FT4 results when changing testing platforms: real-world evidence

PURPOSE

Measurement of thyroid-stimulating hormone (TSH) and free thyroxine (FT4) is important for assessing thyroid dysfunction. After changing assay manufacturer, high FT4 versus TSH levels were reported at Ente Ospedaliero Cantonale (EOC; Bellinzona, Switzerland).

METHODS

Exploratory analysis used existing TSH and FT4 measurements taken at EOC during routine clinical practice (February 2018-April 2020) using Elecsys® TSH and Elecsys FT4 III immunoassays on cobas® 6000 and cobas 8000 analyzers (Roche Diagnostics). Reference intervals (RIs) were estimated using both direct and indirect (refineR algorithm) methods.

RESULTS

In samples with normal TSH levels, 90.9% of FT4 measurements were within the normal range provided by Roche (12-22 pmol/L). For FT4 measurements, confidence intervals (CIs) for the lower end of the RI obtained using direct and indirect methods were lower than estimated values in the method sheet; the estimated value of the upper end of the RI (UEoRI) in the method sheet was within the CI for the UEoRI using the direct method but not the indirect method. CIs for the direct and indirect methods overlapped at both ends of the RI. The most common cause of increased FT4 with normal TSH was identified in a subset of patients as use of thyroxine therapy (72.6%).

CONCLUSIONS

It is important to verify RIs for FT4 in the laboratory population when changing testing platforms; indirect methods may constitute a convenient tool for this. Applying specific RIs for selected subpopulations should be considered to avoid misinterpretations and inappropriate clinical actions.