ODP511 Relationship between TSH and Free Thyroxine in Outpatient Cancer Patient Population

BACKGROUND: The inverse log-linear relationship between TSH and free thyroxine (FT4) is well established and reliably used for evaluation of hypothalamus-pituitary-thyroid axis function. However, there are limited data regarding pathophysiologic states in the TSH-FT4 relationship. The purpose of this study was to evaluate thyroid pituitary hypothalamic feedback regulation by the inverse log TSH and FT4 relationship in cancer patient population at the Ohio State University Comprehensive Cancer Center (OSUCCC-James). METHODS: This retrospective study analyzed the correlation between TSH and FT4 results from 13039 outpatient subjects collected in August 2019-November 2021 at Department of Family Medicine (OSU Wexner Medical Center), Department of Oncology and Department of Chemotherapy (OSUCCC-James). Time of collection for TSH and FT4 was from 7am to 7pm. Data were analyzed by morning (7am-12pm) and afternoon (12pm-7pm). Spearman correlation and non-linear fit were used for data analysis. Sex differences were analyzed as well in each group. RESULTS: No significant differences of TSH or FT4 results were found across all study groups and times in both males and females. Overall, an inverse correlation was observed between TSH and FT4 in the morning and afternoon for both male and female populations in all the three groups. Further analysis by non-linear model in log TSH and FT4 showed a worse fit in the group of Oncology compared to the group of Family Medicine, specifically in the morning data set in both males and females. Interestingly, the inverse non-linear relationship between log TSH and FT4 in the female group designated Chemotherapy showed a better fit in the afternoon, compared with other data sets in the same group. CONCLUSIONS: In cancer patients, the inverse non-linear relationship between TSH and FT4 is weak, which might be resultant of malignancy or medication treatments, or other unknown reasons. The results advance understanding of the pathophysiology and challenges of laboratory diagnosis of thyroid disease in cancer patients. A better understanding of the complex nature of the TSH-FT4 relationship may need further study with better defining subclinical states of cancer patients. Presentation: No date and time listed