Measurement of salivary thyroid hormones using the LC-MS/MS technique in a clinical setting.

Background: Saliva could be an attractive alternative to blood for assessing thyroid hormonal function.

Objectives: Our goal was to determine if the levels of thyroid hormones in saliva can accurately reflect a person's thyroid status and if they consistently correlate with the levels of the same hormones in the blood.

Design: We conducted a cross-sectional study.

Methods: We enrolled a total of 109 participants with different thyroid conditions. We measured TSH (Thyroid-Stimulating Hormone), free T3 (fT3), and free T4 (fT4) in the blood using two different immunoassay methods: electrochemiluminescence immunoassay (ECLIA) and chemiluminescence immunoassay (CLIA). Saliva samples were collected using Salivette^® tubes, and then we analyzed the levels of thyroid hormones in the saliva using liquid chromatography with tandem mass spectrometry (LC-MS/MS).

Results: Comparing salivary and serum levels of thyroid hormones, we observed significantly lower fT4 and higher fT3 levels in saliva (p < 0.001), regardless of the measurement method. We also found that salivary fT3 and fT4 levels were positively correlated in the entire group of participants (p < 0.001, R 0.575), as well as in those with TSH values within the normal reference range (p < 0.001, R 0.570). We further divided participants based on their TSH reference intervals and assessed the correlations between serum and salivary thyroid hormones within these groups. We also discovered that taking exogenous levothyroxine influenced the correlations between serum and salivary thyroid hormones. Thyroid antibodies did not have a significant impact on the levels of thyroid hormones in both serum and saliva.

Conclusion: This study demonstrates that salivary thyroid hormones can partially reflect the levels of these hormones in the blood. Saliva may be a useful tool in a clinical setting for patients with thyroid antibodies, but it may not be as effective for those who are taking levothyroxine as a treatment.