Undertreated Hypothyroidism Linked to Worse Hospital Outcomes

Undertreatment for hypothyroidism was associated with worse hospital outcomes, according to a retrospective cohort study.

Patients with an elevated thyrotropin (TSH) level prior to hospital admission had a length of stay that was 1.2 days longer (95% CI 1.1-1.3) than for patients without hypothyroidism, reported Matthew D. Ettleson, MD, of the University of Chicago, and colleagues in the Journal of Clinical Endocrinology and Metabolism.

Those with a high pre-hospitalization TSH level also had a 49% higher risk of 30-day readmission (risk ratio [RR] 1.49, 95% CI 1.20-1.85) and a 43% higher risk of 90-day readmission (RR 1.43, 95% CI 1.21-1.67).

On the other hand, well-treated patients with hypothyroidism who had normal TSH levels prior to hospital admission had significantly lower risks for both in-hospital mortality (RR 0.46, 95% CI 0.27-0.79) and 90-day readmission (RR 0.92, 95% CI 0.85-0.99).

No differences were seen between people with intermediate or low TSH levels and matched controls 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,” Ettleson said in a statement, noting that this finding had “not been shown previously.”

“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,” he added. “It is particularly important for planned admissions where thyroid hormone replacement can be adjusted if needed prior to admission.”

Using a large commercial claims database of U.S. adults younger than 65, the researchers examined data on 43,478 patients — 8,873 of whom had primary hypothyroidism. Hospital admissions were generally split equally between medical versus surgical.

In general, patients with hypothyroidism tended to be a bit older, were more likely to be women, and had higher rates of diabetes, chronic kidney disease, and rheumatologic diseases. The vast majority were treated with levothyroxine, while some were prescribed liothyronine or desiccated thyroid extract.

Patients with hypothyroidism were classified according to baseline TSH levels prior to hospitalization: low (TSH <0.40 mIU/L), normal (TSH 0.40-4.50 mIU/L), intermediate (TSH 4.51-10.00 mIU/L), and high (TSH >10.00 mIU/L).

Striking a balance when treating TSH levels is important, albeit challenging, as levels that are chronically in the “high” range indicate undertreatment with levothyroxine, while chronically “low” levels suggest overtreatment, Ettleson and team noted.

“Despite the general consensus, off-target serum TSH levels during thyroid hormone replacement have been found in over one-third of patients with primary hypothyroidism in many observational studies,” they wrote.

Those with high TSH levels — indicating undertreatment of their hypothyroidism — may also be more likely to have “suboptimal treatment” for other medical issues, which in turn may contribute to poorer hospital-related outcomes. On top of that, undertreated hypothyroidism alone can also contribute to poorer outcomes on many other organ systems, the researchers said.

While these findings were expected for undertreated patients with hypothyroidism, Ettleson’s group noted that it’s a bit more puzzling why those with pre-hospital TSH levels in the normal range had improved outcomes versus those without hypothyroidism.

“It is unlikely that thyroid hormone replacement would provide an advantage over endogenous thyroid hormone production in hospital outcomes,” they wrote. However, in-range levels may instead act as “a surrogate for regular healthcare and adherence to medical therapy, which likely leads to better hospital outcomes.”