The thyroid is a small gland located in the neck, near the Adam's apple. It consists of two lobes, and tissue called the isthmus which holds them together. The thyroid releases hormones that are important to maintain the body's metabolism by stimulating the cells to increase oxygen use. It also helps to preserve calcium levels in the body, which is important for bone mineralization.
Hormones
The majority of thyroid tests check levels of two different hormones: thyroid stimulating hormone (TSH) and thyroxine (T4). TSH is secreted by the pituitary gland and stimulates the thyroid to release T4. If circulating levels of T4 are low, the pituitary gland senses this and releases more TSH. This maintains thyroid hormone levels throughout the body by using its own feedback mechanism.
Newborn Screening
Newborns in the hospital may have thyroid levels checked by the state's newborn screening program, which detects rare metabolic diseases and hormone deficiencies. Although each state has their own guidelines for testing, most states that do perform the test provide early information for parents about disorders that are present at birth. Detection of low thyroid levels through the newborn screening program helps parents to gain information about treatment and future care.
Hyperthyroidism
Hyperthyroidism occasionally occurs among infants as a result of elevated thyroid levels. According to Merck, mothers who have elevated thyroid levels pass antibodies across the placenta to the developing fetus. Hyperthyroidism causes problems with feedings, irritability and a fast heart rate. Skull and facial changes may also occur, such as small head growth or bulging eyes. Treatment is aimed at reducing levels of thyroid hormone with medication.
Hypothyroidism
Low thyroid levels are known as hypothyroidism. This condition may occur in infants born with underdeveloped thyroid glands, a missing thyroid gland or problems with the pituitary gland in the brain. According to MedlinePlus, hypothyroidism occurs in approximately 1 out of every 3,000 births; and causes a swollen face and tongue, poor muscle tone, feeding difficulties, constipation and jaundice. Untreated, hypothyroidism may lead to mental retardation and slow growth.
Testing
Thyroid levels are checked by taking a blood sample. The baby's heel is pricked with a lancet and a small amount of blood is collected from the site. The blood is analyzed for TSH and T4 levels to determine the need for further testing. Blood collected through a newborn screening program is applied to a specific testing medium. Because other illnesses are tested with the newborn screening program, it may take a couple of days to receive results. Depending on state guidelines, parents are only notified if the results are abnormal.
