Severe Undiagnosed Congenital Hypothyroidism Due to Missed Newborn Screening

We report the case of a 5-month-old female infant with undiagnosed congenital hypothyroidism (CH), presenting with failure to thrive (FTT), hypotonia, developmental delay, and severe constipation. Born full-term as an elective home birth, she had not undergone newborn screening (NBS). Evaluation revealed a markedly elevated thyroid-stimulating hormone (TSH) level and undetectable free thyroxine (T4). Treatment with levothyroxine was initiated at a conservative dosage of 37.5 mcg (7.5 mcg/kg/day) and titrated over time daily to avoid cardiac adverse effects. Nutritional support via nasogastric tube (NG) tube was also initiated due to poor oral intake. Free T4 normalized after 2 weeks, and TSH reached the normal range after 5 weeks, with the goal of maintaining T4 levels on the higher end of normal and TSH on the lower end of normal. By 4 months after the initial admittance, the patient demonstrated significant improvement in weight, progress in occupational therapy and physical therapy, and developmental milestones. This case highlights the significance of verifying NBS in infants with classic signs of CH, especially those born outside of hospital systems, and underscores the value of multidisciplinary collaboration-including social work-in optimizing patient outcome.