Standardization activities in the field of thyroid function tests: a status report.

Item does not contain fulltextBACKGROUND: Laboratory testing is an essential tool for diagnosis and management of thyroid diseases. However, the current status of standardization hampers the interchangeability of results. To improve this situation, the Working Group for Standardization of Thyroid Function Tests was established. METHODS: Method comparisons were organized for measurement of human thyroid stimulating hormone (TSH), and free and total thyroid hormone in serum from apparently healthy donors. The aim was to assess the status of standardization and the quality of the performance of current routine assays. A second objective was to investigate the effect of mathematical recalibration of the results using their relationship to the overall mean (TSH) or the reference measurement procedure values (other thyroid hormones). RESULTS: The need for standardization was shown to be highest for free thyroid hormone and total triiodothyronine measurements, while the majority of TSH and total thyroxine assays agreed within 10% of the reference. Most assays showed good performance. However, some could benefit from improved precision, consistency of calibration, or within- and between-run stability. Recalibration eliminated assay-specific bias. Thus, the residual spread was due to within-method effects. Not withstanding, sample-related effects remained. CONCLUSIONS: These studies confirmed the feasibility of standardization based on method comparison with native sera, but highlighted the need to resolve issues, such as sample-related effects. In view of the fact that in this phase the project worked with samples from individuals with euthyroid status, the next method comparison shall place emphasis on challenging the performance of the assays with clinical samples and expanding the covered measurement range.1 november 201

Characterization and classification of external quality assessment schemes (EQA) according to objectives such as evaluation of method and participant bias and standard deviation. External Quality Assessment (EQA) Working Group A on Analytical Goals ...

Within the scope of this paper, the Working Group has attempted to place external quality assessment (EQA) within the whole context of quality management in laboratory medicine. First, the objectives of EQA schemes are defined and current EQA schemes evaluated. In most schemes, the objectives are not defined a priori and do not allow the definition of the origin of unacceptable individual results from participants. There is an ongoing trend for making traditional EQA schemes more interesting for the participants. Analysis of the factors involved in analytical quality allow the definition of the essential analytical tasks of educational EQA schemes. Beside these quality control tasks, educational EQA also includes quality assurance elements. EQA today has not only an important role to play in the assessment of each participant&#039;s performance but also in the assessment of the method. Efficiency of the schemes and educational impact can be improved by appropriate scheme designs according to objectives. After this theoretical approach, some practical examples of problem related EQA designs are given</p

Controlled polarization switching in intra-cavity contacted VCSELS

We have investigated the potential of asymmetric current injection for polarization switching in GaAs-based intra-cavity contacted vertical cavity surface emitting lasers using two sets of p- and n-contacts per device. We simulated the current paths in both symmetric and asymmetric contacted devices. A large lateral current component is present in the asymmetric case; this induces a certain anisotropy in comparison to the symmetric case, possibly able to stabilize the polarization in one direction. Intra-cavity devices are processed on a standard air-post VCSEL wafer. When using the contacts set along the [1-10] direction, the polarization was set along [110] while using the contacts along [110] the polarization switches from the direction along [110] to a direction making an angle of 25° to 90° towards [110]. This peculiar result can be explained by the fact that the used VCSEL structure is not designed for intra-cavity contacting

Controlled polarisation switching in VCSELs by means of asymmetric current injection

We have investigated the potential of asymmetric current injection for polarisation switching in GaAs-based intra-cavity contacted vertical cavity surface emitting lasers using two sets of p- and n-type contacts per device. When using the contacts set along the [110 ] axis, the polarisation was set along [011] while using the contacts along [011] the polarisation switches from the direction along [011] to a direction making an angle of 25 to 90° towards [011]

Controlled polarization switching in VCSELS by means of asymmetric current injection

We have investigated the potential of asymmetric current injection for polarization switching in GaAs-based intracavity contacted vertical-cavity surface-emitting lasers using two sets of p- and n-type contacts per device. When using the contacts aligned along the [11~0] crystal direction, the observed laser polarization is parallel to [110], whereas, using the contacts along the [110] crystal direction, the polarization of the laser emission switches to a direction making an angle of 25°-90° towards [110]. To overcome this peculiar result, a careful design of the contact layers in the intracavity structure is required

Report of the IFCC Working Group for Standardization of Thyroid Function Tests; part 2: free thyroxine and free triiodothyronine.

Item does not contain fulltextBACKGROUND: Free thyroxine (FT4) and free triiodothyronine (FT3) measurements are useful in the diagnosis and treatment of a variety of thyroid disorders. The IFCC Scientific Division established a Working Group to resolve issues of method performance to meet clinical requirements. METHODS: We compared results for measurement of a panel of single donor sera using clinical laboratory procedures based on equilibrium dialysis-isotope dilution-mass spectrometry (ED-ID-MS) (2 for FT4, 1 for FT3) and immunoassays from 9 manufacturers (15 for FT4, 13 for FT3) to a candidate international conventional reference measurement procedure (cRMP) also based on ED-ID-MS. RESULTS: For FT4 (FT3), the mean bias of 2 (4) assays was within 10% of the cRMP, whereas for 15 (9) assays, negative biases up to -42% (-30%) were seen; 1 FT3 assay was positively biased by +22%. Recalibration to the cRMP eliminated assay-specific biases; however, sample-related effects remained, as judged from difference plots with biologic total error limits. Correlation coefficients to the cRMPs ranged for FT4 (FT3) from 0.92 to 0.78 (0.88 to 0.30). Within-run and total imprecision ranged for FT4 (FT3) from 1.0% to 11.1% (1.8% to 9.4%) and 1.5% to 14.1% (2.4% to 10.0%), respectively. Approximately half of the manufacturers matched the internal QC targets within approximately 5%; however, within-run instability was observed. CONCLUSIONS: The study showed that most assays had bias largely correctable by establishing calibration traceability to a cRMP and that the majority performed well. Some assays, however, would benefit from improved precision, within-run stability, and between-run consistency.1 juni 201

Report of the IFCC Working Group for Standardization of Thyroid Function Tests; part 1: thyroid-stimulating hormone.

Item does not contain fulltextBACKGROUND: Laboratory testing of serum thyroid-stimulating hormone (TSH) is an essential tool for the diagnosis and management of various thyroid disorders whose collective prevalence lies between 4% and 8%. However, between-assay discrepancies in TSH results limit the application of clinical practice guidelines. METHODS: We performed a method comparison study with 40 sera to assess the result comparability and performance attributes of 16 immunoassays. RESULTS: Thirteen of 16 assays gave mean results within 10% of the overall mean. The difference between the most extreme means was 39%. Assay-specific biases could be eliminated by recalibration to the overall mean. After recalibration of singlicate results, all assays showed results within the biological total error goal (22.8%), except for 1 result in each of 4 assays. For a sample with a TSH concentration of 0.016 mIU/L, 6 assays either did not report results or demonstrated CVs >20%. Within-run and total imprecision ranged from 1.5% to 5.5% and 2.5% to 7.7%, respectively. Most assays were able to match the internal QC targets within 5%. Within-run drifts and shifts were observed. CONCLUSIONS: Harmonization of TSH measurements would be particularly beneficial for 3 of the 16 examined assays. These data demonstrate that harmonization may be accomplished by establishing calibration traceability to the overall mean values for a panel of patient samples. However, the full impact of the approach must be further explored with a wider range of samples. Although a majority of assays showed excellent quality of performance, some would benefit from improved within-run stability.1 juni 201

Report of the IFCC Working Group for Standardization of Thyroid Function Tests; part 3: total thyroxine and total triiodothyronine.

Item does not contain fulltextBACKGROUND: Because total thyroid hormone testing is performed on many automated clinical chemistry instruments, the IFCC Scientific Division commissioned the Working Group for Standardization of Thyroid Function Tests to include total thyroxine (TT4) and total triiodothyronine (TT3) in its standardization efforts. METHODS: Existing SI-traceable reference measurement procedures (RMPs) were used to assign TT4 and TT3 values to 40 single-donor serum samples for subsequent use in a method comparison study with 11 TT4 and 12 TT3 immunoassays. Data from comparison of each immunoassay with the RMPs provided a basis for mathematical assay recalibration. RESULTS: Seven TT4 assays had a mean bias within 10% of the RMP, but 2 deviated by an average of -12% and another 2 by +17%. All TT3 assays showed positive biases, 4 within and 8 outside 10%, up to 32%. Mathematical recalibration effectively eliminated assay-specific biases, but sample-related effects remained, particularly for TT3. Correlation coefficients with the RMPs ranged from 0.82 to 0.97 for TT4 and from 0.32 to 0.92 for TT3. The within-run and total imprecision ranges for TT4 were 1.4% to 9.1% and 3.0% to 9.4%, respectively, and for TT3 2.1% to 7.8% and 2.8% to 12.7%, respectively. Approximately one-half of the assays matched the internal QC targets within approximately 5%; however, we observed within-run drifts/shifts. CONCLUSIONS: The study showed that of the assays we examined, only 4 TT4 but the majority of the TT3 assays needed establishment of calibration traceability to the existing RMPs. Most assays performed well, but some would benefit from improved precision, within-run stability, and between-run consistency.1 juni 201

Measurement of free thyroxine in laboratory medicine--proposal of measurand definition.

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