Triiodothyronine as a marker for hemodynamic instability in adolescents with restrictive eating disorders.

Instantaneous vital signs are affected by momentary confounding factors such as anxiety. This study evaluated serum triiodothyronine (T3) levels as a biomarker of hemodynamic instability in 249 adolescents presenting with restrictive eating disorders. Hemodynamic instability was defined as significant bradycardia [minimal heart rate (HR)<50 beats per minute] and/or hypotension [systolic/diastolic blood pressure (BP)<90 mmHg/<45 mmHg]. T3 levels were categorized as normal, low, or extremely low (>4.7, 3.5-4.7, <3.5 pmol/L, respectively). Adolescents with low (74, 30%) or extremely low (125, 50%) T3, as compared to those with normal levels, had significantly lower HR (p = .004), lower BP (p < .001), greater weight loss (p = .02), longer hospital stay (p = .01), and longer duration of amenorrhea (p = .01). T3 levels showed significant negative correlations with weight loss (r = -0.2, p = .004). As a biomarker less susceptible to acute confounding factors than vital signs, T3 may enhance clinical assessment and risk stratification at initial presentation.