What is the most appropriate method of diagnosing primary congenital hypothyroidism in a newborn?

The most appropriate method for diagnosing primary congenital hypothyroidism in a newborn is through heel stick serum T4 and thyroid-stimulating hormone (TSH) concentration measurements. This testing is typically performed as part of newborn screening programs shortly after birth, often within the first few days.

Congenital hypothyroidism may not present with noticeable clinical symptoms initially, as many infants appear normal in the early days of life. Therefore, relying on clinical presentations alone is not sufficient for making a diagnosis, as symptoms like hypothermia, hypotonia, myxedema, lethargy, umbilical hernia, and poor feeding can be indicative of various other conditions and are not specific for hypothyroidism.

By measuring serum T4 and TSH, clinicians can assess the function of the thyroid gland effectively. An elevated TSH level, coupled with a low T4 level, indicates primary congenital hypothyroidism. Early diagnosis is crucial, as timely treatment with thyroid hormone replacement can prevent developmental delays and long-term complications associated with untreated congenital hypothyroidism.

Using umbilical cord serum T4 concentration is less common and may not always reflect the thyroid function of the newborn accurately, since factors affecting maternal thyroid function could also influence cord blood measurements. Therefore