When thyroid nodules are found clinically or incidentally on imaging, the patient’s thyrotropin level should be measured.1 Ultrasound is the first-line imaging recommended to assess thyroid nodules.1,2 Nodules can then be evaluated by a fine-needle aspiration (FNA) biopsy, which provides cytological information to determine whether the nodule is benign or malignant.1,3,4 Most thyroid nodules pose a low risk of malignancy.1
The American Thyroid Association guidelines on thyroid nodule management do not specify any recommendations for follow-up thyrotropin testing in patients who do not have any history that is known to affect thyroid function.1 Therefore, clinicians have to make decisions regarding follow-up testing in these patients without any evidence-based guidelines. There is a lack of data in the literature on whether thyrotropin levels change over time in this patient population. If thyrotropin levels do not become abnormal over time, then patients would not need thyrotropin monitoring or treatment for hypo- or hyperthyroidism.
The aim of this study was to determine whether thyrotropin levels change over time in patients with thyroid nodules and determine whether repeat thyrotropin testing was required after initial testing. The authors hypothesized that thyrotropin values do not change substantially over time in patients with thyroid nodules, except in patients with a history of hot nodules, autoimmune thyroid disease, thyroid or pituitary surgery, radioactive iodine ablation, neck radiation, or use of medications affecting thyroid function. This study may be able to contribute to the clinical guidelines for thyrotropin testing in patients with thyroid nodules so that clinicians can make evidence-based decisions.
METHODS
This retrospective chart review was conducted using the Computerized Patient Record System at the Veterans Affairs Dayton Healthcare System (VADHS) in Ohio. Patients aged ≥ 18 years who were diagnosed with ≥ 1 thyroid nodule from January 2010 to December 2016 and had a normal thyrotropin level at the time of diagnosis were included in the study. Patients who were found to have thyroid nodules multiple times were included only once from the time of the initial diagnosis. Patients were excluded if they had a medical history known to affect thyroid function. Exclusion criteria included a history of hot thyroid nodules; autoimmune thyroid disease on imaging or blood work; history of thyroid surgery, including pituitary surgery; history of radioactive iodine treatment; history of neck radiation; use of thyroxine before nodule diagnosis; use of amiodarone, programmed cell death-1 inhibitors, programmed cell death ligand-1 inhibitors, or cytotoxic T-lymphocyte-associated protein-4 inhibitors; or 3 consecutive months of steroid use.
Age at nodule diagnosis, sex, race, thyrotropin values at and after the time of nodule diagnosis, and duration from nodule diagnosis to most recent thyrotropin value were retrospectively collected until 100 patients met inclusion criteria for the study. Of note, from 2010 to 2016, the assays used at the VADHS to measure thyrotropin values changed over time, as did the normal reference ranges and the type of sample used for the assays. Normal thyrotropin range at time of diagnosis based on serum or plasma samples and for repeat thyrotropin levels are provided in Table 1, also based on serum or plasma samples. All collected data in the study was de-identified for analysis.
Statistical Analysis
Patients were divided into 2 groups: those who had an abnormal most recent thyrotropin value and those who did not. Mean (SD) of both groups was calculated for continuous variables of age at diagnosis, initial thyrotropin value and most recent thyrotropin value, and time from diagnosis to most recent thyrotropin value. Percentages for both groups were calculated for categorical variables of sex, race, and whether initial and most recent thyrotropin values were based on serum or plasma samples and old or new reference ranges. A 95% CI was determined for the true population rate of patients with an abnormal thyrotropin value at most recent testing. Independent sample t tests were used to compare the continuous variables between the abnormal and normal most recent thyrotropin groups. Categorical variables between the 2 groups were compared using χ2 tests. P < .05 was considered statistically significant. Statistical analyses were completed using IBM SPSS Statistics 27. This study was approved by the Wright State University Institutional Review Board and the VADHS Research and Development Committee.