Thyroid Function Testing in Hospitalised Patients: Non-Thyroidal Illness and the Test That Should Not Have Been Sent

Abstract

Thyroid function testing in an acutely unwell hospitalised patient is frequently confounded by non-thyroidal illness syndrome, a
pattern of altered thyroid hormone results driven by the systemic illness itself rather than by primary thyroid disease, yet thyroid
panels continue to be ordered and acted upon in this setting at a rate that outpaces the clinical value the result actually adds. We
review the pathophysiology and recognised patterns of non-thyroidal illness syndrome, then examine ordering and action-taken
data from a 3,240-admission acute medical cohort. Thyroid function tests were ordered in 18.6% of admissions, and of the
abnormal results returned, 61.2% were judged retrospectively to reflect non-thyroidal illness rather than primary thyroid disease,
yet 22.4% of these prompted either endocrine referral or a change in thyroid medication before the acute illness had resolved. We
set out the specific result patterns that distinguish non-thyroidal illness from genuine thyroid dysfunction and argue for deferred
rather than acute-phase thyroid testing wherever clinically feasible.