How is the condition diagnosed?

Babies are screened in the first days of life for a variety of conditions. The heel prick or Guthrie test (where a small drop of blood is taken for testing) is usually performed by the midwife in the first 24 to 72 hours after birth.

Measurement of TSH or thyroxine (T4) is taken on the second or third day of life . If the TSH is high, or the T4 low, the infant's doctor and parents are called and a referral to a pediatric endocrinologist is recommended to confirm the diagnosis and initiate treatment. Often a technetium (Tc-99m pertechnetate) thyroid scan is performed to detect a structurally abnormal gland. The Tc-99m pertechnetate exam will help differentiate congenital absence or a defect in organification (a process necessary to make thyroid hormone).

Sometimes the doctor will order X-rays of the baby's legs to show the bone ends at the knee joints. These can show immature appearances in babies who have hypothyroidism, and helps to confirm a diagnosis.