The inaccuracy of 17-β estradiol (E2) measurements affects its use as a biomarker in patient care and research. Clinical and research communities called for accurate and standardized E2 measurements. Reference Measurement Procedures (RMPs), part of the CDC Hormone Standardization Program (HoSt), are essential in addressing this need and ensuring that methods are accurate and comparable across testing systems, laboratories, and over time. A candidate RMP (cRMP) was developed for the measurement of total E2 in serum using liquid chromatography-tandem mass spectrometry (LC-MS/MS) without derivatization. The cRMP meets suggested performance criteria for accuracy and precision through the use of isotope dilution, calibrator bracketing, and gravimetric measurements. The cRMP demonstrated high agreement with certified reference materials (no significant bias to BCR576, 577, and 578) and established RMPs (slope 1.00, 95% CI 1.00–1.01; intercept 0.02, 95% CI -0.01 to 0.06). The cRMP is highly precise with intra-assay, interassay, and total percent CVs of 2.7%, 1.3%, and 2.4%, respectively. A higher specificity was achieved by measuring E2 without derivatization, compared to methods using derivatization agents. The cRMP can serve as a higher-order standard for establishing measurement traceability and provides an accuracy base against which routine methods can be compared in HoSt.

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Reliable FT4 measurement is critical to assess thyroid function and diagnose and treat thyroid disorders. The Partnership for the Accurate Testing of Hormones (PATH) categorizes FT4 as a biomarker in high need for standardization, and currently high inter-assay variability restricts the interpretation of FT4 results in patient care to assay-specific reference intervals. The CDC CSP has partnered with the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) and PATH to create a standardization program for FT4 to improve accuracy, reliability, and comparability of current methods and thus to improve diagnosis, treatment and prevention of thyroidal illnesses. Currently, there are no serum FT4 reference materials available to assess the accuracy and reliability of FT4 assays. CDC has developed an accurate and sensitive reference measurement procedure (RMP) to create commutable serum reference materials with FT4 target values. Assay manufacturers, research and clinical laboratories can use these reference materials to assess their calibration, certify the analytical performance of their measurements, and monitor performance over time by collaborating with CDC CSP. The CDC FT4 RMP uses equilibrium dialysis (ED) with LC-MS/MS based on an internationally recognized ED procedure[1] followed by solid-phase and solvent extractions. Certified primary reference material IRMM468 was used to prepare calibrators. Chromatographic separation is achieved with a gradient of methanol and water with 0.1% formic acid. FT4 is quantified using positive electrospray ionization in positive mode. The intra- and inter-day imprecision of the CDC RMP are 3.0% and 1.1%. A comparison among FT4 RMPs resulted in a +2.5% bias for the CDC RMP to the mean for all labs. The CDC RMP measurement range was 3.02-258 pmol/L and thus suitable for analysis of hypo- and hyperthyroid patients. The CDC FT4 RMP demonstrates good accuracy and precision, and can be used as a viable accuracy base to which routine methods can be compared. An initial comparison study of a commercially available FT4 immunoassay (IA) and the CDC RMP with 24 samples (7.98-109 pmol/L) indicated a mean bias of -37.7%, further indicating a need for standardization. Findings from an IFCC study suggest that alignment of IA measurements to a FT4 RMP can improve comparability and would allow for a uniform reference interval for FT4.[2] CDC CSP established a new standardization program for FT4 to address the needs of the community and assist with improving test comparability and reliability.1. Clin. Chem. Lab. Med. 2011, 49: 1275-81. 2. Clin. Chem. 2017, 63: 1642-52.