When screening shows low T4 and elevated TSH, thyroid hormone therapy should be started as soon as blood is collected for serum confirmation tests. Which option describes this timing?

• A. After confirmation testing is completed
• B. As soon as blood is collected for serum confirmation tests
• C. Only if symptomatic
• D. After 1 week

Answer: (B)

Low T4 with elevated TSH in a newborn points to congenital hypothyroidism, a condition where early thyroid hormone replacement is crucial for normal brain development. The neurodevelopmental window is very sensitive in the first weeks of life, and delays in treatment can lead to irreversible deficits. Because confirmatory tests take time, therapy should begin promptly rather than waiting for results. Starting thyroid hormone as soon as blood has been drawn for serum confirmation tests ensures treatment starts without unnecessary delay, optimizing outcomes. Delaying therapy—whether until after full confirmation, only if symptoms are present, or after a week—can risk neurodevelopmental impairment.