Measurement of reverse triiodothyronine levels using liquid chromatography-tandem mass spectrometry in the serum of 89 outpatients

抄録

Background: Reverse triiodothyronine (rT3) has useful clinical applications, such as differentiating euthyroid sick syndrome from hypothyroidism. However, rT3 measurement is unavailable in the clinical setting in Japan. Therefore, we assessed the feasibility of using liquid chromatography–tandem mass spectrometry (LC–MS/MS) for measuring serum rT3 levels in outpatients.

Method: MS/MS detection was performed in the positive ionization mode on a tandem quadrupole mass spectrometer equipped with an electrospray ionization interface. The precursor–product ion pairs of rT3 (m/z 652→508) and ¹³C₆-rT3 (m/z 658→514) were selected. Quantification was performed via selected reaction monitoring using peak areas. The serum from 89 patients (age, 8.1±8.1 years) who visited Aichi Medical University was collected. Patients diagnosed with thyroid disease were excluded. rT3 was extracted from 100 μL of patient serum by liquid–liquid extraction. ¹³C₆-rT3 was used as the internal standard. Serum rT3 levels were also determined using a radioimmunoassay (RIA) kit.

Result: The lower limit of rT3 quantification was 0.02 ng/mL. The relative standard deviation and relative error were <9% and <4%, respectively, indicating an acceptable level of reproducibility. Compared with RIA, LC–MS/MS exhibited superior linearity (0.99872 versus 0.99999). rT3 levels in the patient serum samples were in the range of 0.038–0.853 ng/mL.

Conclusion: The LC–MS/MS technique reliably measured rT3 in the serum of 89 outpatients.