Feasibility Study of the Use of Frozen Human Sera in Split-Sample Comparison of Immunoassays with Candidate Reference Measurement Procedures for Total Thyroxine and Total Triiodothyronine Measurements

Abstract

Background: Diagnostic manufacturers must ensure/ document metrologically traceable assays. We report on a feasibility study of a split-sample comparison for that purpose. Processed, frozen single-donation sera, assigned target values by candidate reference measurement procedures (cRMPs), were used with immunoassays for total thyroxine (TT 4 ) and triiodothyronine (TT 3 ) as models. Methods: Two serum panels were quantified for TT 4 and TT 3 with validated cRMPs and measured in parallel with at least 14 immunoassays. The results were interpreted in terms of traceability of calibration (trueness) and of the individual measurement result (accuracy) by linear regression analysis and graphical representation against specifications. The commutability of the sera was investigated by parallel analysis of TT 4 in freshly collected but nonfiltered specimens. Results: The TT 4 (TT 3 ) concentrations in the sera (according to the cRMPs) were 64 -269 nmol/L (0.88 -13.7 nmol/L). The method comparison showed that for TT 4 , on average, the immunoassays produced results in agreement with the cRMPs, whereas for TT 3 , results were typically higher. It also demonstrated a consider-

Report of the IFCC Working Group for Standardization of Thyroid Function Tests; Part 3: Total Thyroxine and Total Triiodothyronine

“…Compared with previously performed large-scale studies, the overall picture for TT4 revealed in this study was similar (6,16 ). For TT3, however, results of only 1 study showed a similar positive bias for the majority of assays (6 ), whereas results of another study demonstrated a negative bias (16 ).…”

“…For TT3, however, results of only 1 study showed a similar positive bias for the majority of assays (6 ), whereas results of another study demonstrated a negative bias (16 ). It should be men- Special symbols are used for the assays with the strongest negative (circles) and positive bias (triangles).…”

“…The systems comprise T4/T3 primary calibrators and trueness-based isotope dilution-liquid chromatography/tandem mass spectrometry (ID-LC/tandem MS) reference measurement procedures (RMPs). In addition, the feasibility of standardization (establishing SI traceability) of TT4/TT3 routine assays has already been demonstrated (6 ). The reference measurement systems (inclusive reference measurement services) are listed in the database of the Joint Committee for Traceability in Laboratory Medicine (7 ).…”

Proficiency Testing/External Quality Assessment: Current Challenges and Future Directions

“…The C37A protocol has not been validated to produce samples that are commutable with patient samples for other analytes but represents the best available approach and has been used to prepare single-donor serum samples and pools for several investigations of the trueness of measurement procedures for several analytes (17)(18)(19)(20)(21). Thienpont et al found that processing of serum (e.g., sterile filtration, storage before aliquoting and freezing) may disturb the equilibrium between free and protein-bound thyroid hormone and hence jeopardize the commutability of a reference material prepared even from sera that has been subjected to minimal processing (22 ). Rigorous protocols for other matrices have not been reported, but the general principle to collect unaltered samples, pool them, and either distribute and measure aliquots immediately or freeze aliquots at ՅϪ70°C is accepted as the best available approach to obtain PT/EQA samples likely to be commutable.…”

Assessment of human thyroid function using radioimmunoassay and enzyme-linked-immuno-sorbent-assay

“…the production of this hormone is not possible without stimulation from the TSH which in turn is also regulated by the hypothalamus's thyrotropin-releasing hormone. Thyroid function tests have been dependent on an indirect estimate of the serum total thyroxin (T4) concentration, using protein bound iodine (PBI) technique by 1950s (Benotti and Benotti, 1963); however since 1970s to recently there are many applied techniques such as: Radioimmunoassay (RIA) (Baloch et al, 2003), immunometric assay (IMA) (Spencer et al, 2005;Thienpont et al, 2007) and more recently liquid chromatography-tandem mass spectrometry (LC-MS/MS) methodologies (Dufour, 2007;Kahric-Janicic et al, 2007) which have progressively improved the specificity, reproducibility and sensitivity of thyroid testing methods (Thienpont et al, 2005 Thyroid function test has been the most popular test to diagnose an overactive or underactive thyroid gland (hyperthyroidism or hypothyroidism), monitoring response to thyroid therapy (Dayan, 2001;Midgley, 2001;Jostel et al, 2009). In this realm Ingwersen et al (1992) eliminated the protein ANP-270 using RIA and ELISA in which the half-life of elimination was found to be 123 and 6 minutes respectively, these discrepancies were shown to be due to fragments of ANP-270 cross-reacting in the RIA but not in the ELI-SA.…”