Certification of a pregnancy-specific reference material for thyroid biomarkers, vitamin D, and nutritional trace elements in serum
Ashley S. Boggs-Russell, Lisa E. Kilpatrick, Carolyn Q. Burdette, Denise S. Tevis, Zachary A. Fultz, Michael A. Nelson, Jeff M. Jarrett, Stephen A. Wise, Brittany Kassim, Stephen E. Long
Background Concentrations of critical metabolites, hormones, and nutritional elements change significantly throughout pregnancy. Therefore, increased matrix complexity is a challenge for the measurement of these biomarkers. To provide a quality assurance material to underpin clinical health assays and calibration of secondary standards, Standard Reference Material (SRM) 1949, Frozen Human Prenatal Serum, was developed. Methods Serum pools from non-pregnant women and women in each trimester were bottled into four levels. New liquid chromatography tandem mass spectrometry (LC-MS/MS) methods were developed and applied to the measurement of total thyroxine (T4), total tri-iodothyronine (T3), total reverse tri-iodothyronine (rT3), vitamin D metabolites, and vitamin D binding protein (VDBP). Copper, selenium, and zinc measurements were conducted by inductively coupled plasma-dynamic reaction cell-mass spectrometry (ICP-DRC-MS). Thyroid stimulating hormone (TSH) and thyroglobulin (Tg) concentrations were analyzed using different commercially available immunoassay kits and serum dilution factors to explore potential inaccuracies. Results Certified values for T4 and T3, were assigned to all levels. Reference values were assigned for three vitamin D metabolites, VDBP, selenium, copper, and zinc. Information values were described for rT3, Tg, and TSH. Changes in matrix qualities are evident by significantly different concentrations (p ≤ 0.003) of all analytes measured across the four levels. TSH concentrations were significantly different (p ˂ 0.0001) among kits depending on the dilution factor or immunoassay test manufacturer. Tg concentrations were higher than previously recorded in the literature regardless of dilution factor. Conclusion These results demonstrate the necessity of having a matrix matched reference material specific for pregnancy health diagnoses.