Two-step thyroid screening strategy in the critical patient

Thyroid function biochemical tests are known for their usefulness in prognosis of long-term critical patients, although current data are controversial regarding the clinical benefit of both free triiodothyronine and thyroxine as prognostic thyroid markers during the first 48h after Intensive Care Unit (ICU) admission.

The aim of this study was to evaluate the usefulness of two strategies for thyroid function assessment in the first 48h after admission at the ICU. The usefulness of a two-step biochemical thyroid strategy (initial isolated TSH determination, followed by subsequent fT4 and fT3) was compared with a complete one-step biochemical profile (TSH+fT4+fT3).

No significant differences were found between the rates of thyroid dysfunction detection when using both strategies (2.8% vs. 2.4%; p=0.71). Using the two-step strategy and a 2.5μUI/mL cut-off value for TSH, sensitivity and negative predictive value were 100%. Among patients with an altered fT3 only, mortality was 14% if TSH≤2.5μUI/mL, whereas it was 7% if TSH>2.5μUI/mL (p=0.008).

For patients with critical illness, the early two-step thyroid screening strategy (starting with an isolated TSH determination between 24 and 48h after admission) led to a saving of 50% in fT4 and fT3 tests, with a false-negative rate of 1.3%. This represents an improved diagnostic approach, hence avoiding the performance of unnecessary complementary biochemical measurements.