Assay of Free Thyroxine and Free Triiodothyronine in Fine-Needle Aspiration of Thyroid Nodules: a Useful and Low-Cost Assessment

ObjectiveTo evaluate whether analysis of thyroid hormones in fine-needle aspiration (FNA) of thyroid nodules can provide information about the functional status and the nature of the nodules.MethodsWe studied 4 groups of patients: group 1, 17 patients with autonomous hyperfunctioning thyroid nodules; group 2, 52 patients with cold nonfunctioning thyroid nodules; group 3, 12 patients with malignant thyroid nodules; and group 4 (control group), 10 patients with nonthyroid nodular lesions (enlarged parathyroid glands or lymph nodes). The assay of thyroid hormones was performed in FNA after the washing of needles and, with patient consent, also in normal thyroid parenchyma.ResultsThe free thyroxine (FT₄) and free triiodothyronine (FT₃) values were remarkably high in group 1 (mean, 5.5 ± 0.53 ng/dL and 27.6 ± 3.1 pg/mL, respectively; P < 0.05 versus group 2 and group 4, the control group). The levels of FT₄ and FT₃ were very low in group 3 (< 0.2 ng/dL and < 1.0 pg/mL, respectively; P < 0.05 versus group 2). Thyroglobulin values in FNA specimens were much higher than the normal range in human serum, but no significant differences were found between the various groups. The control group had low levels of FT₄ and FT₃ (< 0.2 ng/dL and < 1.0 pg/mL, respectively) in conjunction with low levels of thyroglobulin, whereas parathyroid hormone levels were high in parathyroid nodules.ConclusionThese results show that assay of FT₄ and FT₃ in FNA can yield information about the functional status of thyroid nodules and, indirectly, about the nature of nodules. In this era of sophisticated new molecular markers in FNA cytology, this low-cost diagnostic method can be readily performed in every laboratory. (Endocr Pract. 2004;10:311-316)