Undertreatment of Hypothyroidism Increases Risk of Adverse Hospital Outcomes

Matthew Ettleson, MD

A new study from the University of Chicago suggests under treatment with thyroid hormone replacement may be contributing to worse hospital outcomes among patients with hypothyroidism.

A retrospective cohort study using propensity scoring, investigators assessed risk of adverse hospital outcomes among patients with hypothyroidism according to levels of thyroid-stimulating hormone (TSH) prior to admission and found those with high TSH levels had longer length of stay and higher risk of readmission compared to those without hypothyroidism.

“We found that those patients who were undertreated with thyroid hormone, even weeks or months prior to hospital admission, had worse hospital outcomes than those without hypothyroidism,” said Matthew D. Ettleson, MD, an endocrinology fellow at the University of Chicago, in a statement from the Endocrine Society. “This has not been shown previously.”

Partially funded by the National Institute of Diabetes and Digestive and Kidney Diseases, the current study was designed by Ettleson and colleagues to assess the impact of suboptimal treatment of hypothyroidism on hospital outcomes. A retrospective cohort study using data from the IBM MarketScan Commercial Claims and Encounters Database from 2008-2015, investigators obtained data from 43,478 patients for inclusion on their analyses.

For inclusion in the investigators’ analyses, patients needed to be 64 years of age or younger with TSH levels recorded prior to hospital admission. Of the 43,478 patients identified for inclusion, 8873 met the criteria for having primary hypothyroidism. Of those with primary hypothyroidism, 53.8% had a prescription claim for levothyroxine, 23.7% had a levothyroxine prescription only, and 21.8% had a diagnosis of hypothyroidism only. Investigators noted the median length of time between TSH collection and hospital admission was 56 days in the hypothyroidism group and 63 days in the control group.

For the purpose of analysis, investigators divided patients with hypothyroidism into 4 groups based on TSH levels. These groups were classified as low, normal, intermediate, and high, with TSH levels of less than 0.40 mIU/L, 0.40-4.50 mIU/L, 4.51-10.00 mIU/L, and greater than 10.00 mIU/L, respectively, defining each group.

The primary outcomes of interest for the study were length of stay, in-hospital mortality, and readmission outcomes. Covariates used in investigators' analyses included age, sex, US region, type of admission, year of admission, and comorbidities.

When compared to those without hypothyroidism at baseline, those with a high prehospitalization TSH level had longer lengths of stay, a 49% greater risk of 30-day readmission, and a 43% greater risk of 90-day readmission (RR, 1.43 [95% CI, 1.31-1.67]; P <.001). Further analysis comparing those with normal TSH levels to those with elevated prehospitalization TSH levels indicated patients with normal levels had a decreased risk of in-hospital mortality (RR, 0.44 [95% CI, 0.27-0.79]; P=.004) and 90-day readmission (RR 0.92 [95% CI, 0.85-0.99]; P=.02) than their counterparts with elevated levels.

“The results suggest that suboptimal treatment of hypothyroidism is associated with worse hospital outcomes,” Ettleson said. “It is important for both patients and physicians to know that maintaining optimal thyroid hormone replacement is important to minimize length of hospital stays and hospital readmission. It is particularly important for planned admissions where thyroid hormone replacement can be adjusted if needed prior to admission.”

This study, “Suboptimal Thyroid Hormone Replacement is Associated with Worse Hospital Outcomes,” was published in the Journal of Clinical Endocrinology and Metabolism.