Fine-needle aspiration (FNA) is the most appropriate next step in the evaluation to determine whether this patient's thyroid nodule is malignant or benign. She has already had an ultrasound examination. Ultrasonography is a sensitive means of identifying nodules and providing further characterization of the nodules, which is more predictive of malignancy than size alone. The ultrasonographic features that are considered more suspicious for malignancy include hypoechogenicity, microcalcifications, irregular margins, and increased intranodular Doppler flow. According to American Thyroid Association guidelines, this patient with a hypoechoic nodule that is 1.5 cm should have an FNA to rule out malignancy.

Nodular features are not readily identified on CT, and this study has a lower sensitivity than ultrasonography for identifying the presence of nodules. CT of the neck would therefore not provide any additional information about this patient, who has already had an ultrasound examination. In addition, CT would expose this patient to unnecessary radiation. If a patient has a substernal goiter, CT is beneficial for determining the extent of the goiter. However, this patient has no extension of the thyroid into the mediastinum.

Levothyroxine therapy to suppress growth of benign nodules is no longer recommended. Randomized clinical trials have failed to show a significant effect on nodule volume. Additionally, the required dose can induce thyrotoxicosis, which is associated with significant risk for cardiovascular complications.

Measurement of the serum thyroglobulin level is reserved for patients who have had a total thyroidectomy and is useful as a tumor marker for detection of residual or recurrent thyroid cancer. In a patient with an intact thyroid, serum thyroglobulin measurement is an insensitive and nonspecific means of testing for malignancy.

Thyroid scanning with technetium is unlikely to be helpful in this patient. Thyroid scanning is used to determine the functional status of the nodule. Isotope scanning is most useful in the setting of a nodule accompanied by a low serum thyroid-stimulating hormone level because toxic (or hyperfunctioning) nodules typically do not require FNA as the vast majority are benign. This patient has a normal serum thyroid-stimulating hormone level and is likely to have an indeterminate result (“cold” or “warm”) on thyroid scanning.