Things We Do for No Reason™: Routine Thyroid-Stimulating Hormone Testing in the Hospital

The most important confounder of thyroid function testing in the hospital is nonthyroidal illness syndrome (NTIS), also known as sick euthyroid syndrome. Although the prevalence of unrecognized thyroid disease in hospitalized patients is 1%-2.5%,¹¹ NTIS is observed in up to 62% of hospitalized patients and not exclusively in critically ill patients as previously thought.⁸ Risk factors include infection, stroke, myocardial infarction, kidney or liver injury, burns, malnutrition, malignancy, and recent surgery, as well as multiple medications.¹² Contributing factors may include the effect of cytokines on thyroid-releasing hormone and TSH secretion, decreased deiodinase activity, and changes in thyroid hormone receptor activity.⁸ No one pattern of thyroid function testing is pathognomonic of NTIS.^8,12

The high prevalence of NTIS reduces the specificity of TSH testing in hospitalized patients. In this population, Attia et al. determined that mild abnormalities (TSH 0.1-0.6 mIU/L or 6.7-20 mIU/L) have a positive likelihood ratio (LR+) of true thyroid disease of 0.0 and 0.74, respectively, counterintuitively reducing rather than increasing the posttest probability of thyroid disease. Although TSH levels <0.01 and >20 mIU/L carry a higher LR+ (7.7 and 11.1, respectively), the vast majority of abnormal TSH results in the hospital are mild, self-resolving, and do not change clinical management.^5,11,13 Adlan et al. reported that only 1.2% of tested patients have very abnormal TSH results (4/751 with TSH <0.01 and 5/751 with TSH >10 mIU/L).⁵

Spencer et al. measured TSH and other thyroid function tests in 1,580 adult patients admitted to a large county hospital in the United States, without regard to symptoms or prior diagnosis of thyroid disease. They found that 519/1,580 (33%) had TSH values outside the laboratory reference range. Of the 1,580 patients, 329 were randomly selected for further analysis, and 29/329 (8.8%) were found to have true thyroid disease. The vast majority of these patients (22/29, 75.8%) had TSH levels <0.1 mIU/L or >20 mIU/L. Importantly, the authors did not indicate how many of the 29 patients had known preexisiting thyroid disease or clinical symptoms.¹³

Similarly, an Israeli study examined the utility of routine TSH testing upon admission to an internal medicine service. More than 1 in 10 patients had abnormal TSH results (11.8%, 232/1,966). After chart review, the majority of the abnormal results (52.2%, 121/232) were felt to be secondary to NTIS. Subclinical thyrotoxicosis and subclinical hypothyroidism were noted in a further 20.7% (48/232) and 18.5% (43/232) of the patients, respectively. Overall, in only nine patients (0.5%, 9/1,966) did TSH testing lead to a change in clinical management. In all these cases, patients were either already on a medication known to affect thyroid function (eg, levothyroxine, amiodarone) or the pretest probability of thyroid-related illness was elevated because of clinical presentation.⁴

Several institutions have implemented quality improvement (QI) initiatives to reduce inappropriate thyroid function testing without apparent compromise to clinical care.¹⁴ Although none included balancing measures within their QI design, the implementation of simple appropriateness guidelines, for example, has been shown to reduce the frequency of TSH ordering by as much as 50%, which suggests significant overtesting.^5,15,16 Similarly, in a clustered randomized control trial, Thomas et al. demonstrated a significant reduction (odds ratio [OR] 0.82) in outpatient TSH ordering after the addition of a simple educational message to the order.¹⁷