A method for simultaneous determination of triiodothyronine and thyroxine in fingernail clippings by LC/ESI-MS/MS.

A fingernail clipping is a promising specimen for evaluating the medium-to-long term status of low-molecular weight hormones. However, the nail concentrations of thyroid hormones and their clinical significance remain poorly understood. In this study, a liquid chromatography/electrospray ionization-tandem mass spectrometry (LC/ESI-MS/MS) method was developed and validated for simultaneously quantifying triiodothyronine (T3) and thyroxine (T4) in the thumbnail clippings. The nail T3 and T4 were extracted with 50 % ethanol and purified using a Strata-X cartridge, then injected into the LC/ESI-MS/MS. 13C6-T4 was used as the internal standard for both T3 and T4. Validation results demonstrated that the method was precise (relative standard deviations in five repetitive measurements were ≤ 4.5 %) and accurate (analytical recovery rates were 98.3-103.3 %). The lower limits of quantification were 0.20 ng/g for both thyroid hormones. By using this method, we found that the nail concentrations of T3 (0.74 ± 0.26 ng/g, mean ± standard deviation) were at the same level as those of T4 (0.90 ± 0.27 ng/g) in euthyroid subjects (n = 40). This result might be caused due to the greater free and albumin-bound fractions of circulating T3 compared to T4. The patients with Graves' disease showed significantly higher nail T3 and T4 concentrations than the euthyroid subjects. The patients with hypothyroidism due to Hashimoto's thyroiditis tended to have lower nail T3 and T4 concentrations compared to the euthyroid subjects. Thus, the developed method would be useful for evaluating the medium-to-long term status of thyroid hormone production and has sufficient clinical applicability.