Method specific second-trimester reference intervals for thyroid-stimulating hormone and free thyroxine

ObjectiveTo determine second trimester reference intervals for TSH and FT4.DesignSamples from 3102 subjects were tested for TPO and Tg antibodies.MethodsElecsys E170 reference intervals for TSH and FT4 were determined using antibody-negative samples.ResultsSecond trimester reference intervals for TSH and FT4 were 0.18–4.07 mIU/L and 9.5–15.8 pmol/L, respectively. The Elecsys E170 TSH results were positively biased compared to ARCHITECT i2000SR results for these same samples.ConclusionsMethod-specific reference intervals are required for TSH and FT4.