NEONATAL SCREENING (TSH)

Neonatal Screening (TSH) is a newborn blood test that measures Thyroid-Stimulating Hormone to identify babies who may require further evaluation for congenital hypothyroidism. Congenital hypothyroidism occurs when a baby is born with inadequate thyroid-hormone production or, less commonly, impaired hormonal regulation of the thyroid gland.

Thyroid hormone is essential for normal brain development, physical growth and metabolism. Many affected newborns appear healthy and show no obvious symptoms during the first days of life. Screening is therefore important because it can identify a possible problem before clinical signs become evident.

The test is commonly performed using a few drops of blood collected from the baby's heel and applied to a specialised filter-paper card. Depending on the laboratory and clinical situation, TSH may instead be measured using a venous blood sample. An abnormal screening result does not confirm congenital hypothyroidism; prompt confirmatory testing is required.

Benefits of the Test

• Supports early identification of newborns at risk of congenital hypothyroidism.
• Can detect possible thyroid dysfunction before symptoms become apparent.
• Uses only a few drops of blood when performed as a heel-prick blood-spot test.
• Allows timely referral for confirmatory thyroid-function testing.
• Supports early treatment when congenital hypothyroidism is confirmed.
• Helps reduce the risk of preventable developmental and growth complications.
• Can be included within a broader newborn-screening programme.
• Provides clinically important information during the early newborn period.

Why Doctors Recommend This Test

Doctors recommend neonatal TSH screening because congenital hypothyroidism may not cause noticeable symptoms immediately after birth. Without screening, diagnosis may be delayed until feeding, growth or developmental problems become apparent.

TSH is produced by the pituitary gland and signals the thyroid gland to produce thyroid hormones. In many babies with primary congenital hypothyroidism, thyroid-hormone production is low and the pituitary responds by releasing more TSH. An elevated newborn TSH result may therefore indicate that confirmatory testing is needed.

Possible causes of primary congenital hypothyroidism include an absent, underdeveloped or abnormally positioned thyroid gland and inherited problems affecting thyroid-hormone production. Some abnormal newborn thyroid results are temporary and may be associated with prematurity, illness, iodine exposure, maternal thyroid disease or medicines.

Early identification is important because untreated congenital hypothyroidism can affect brain development, growth and other body functions. When the condition is confirmed and treatment begins promptly, developmental outcomes can be substantially improved.

TSH-only screening is designed mainly to identify primary congenital hypothyroidism. It may not detect every case of central hypothyroidism, in which the pituitary or hypothalamus does not provide adequate stimulation. Screening methods and follow-up protocols therefore vary between newborn-screening programmes.

Preparation Before Test

No fasting is required. The baby can generally continue breastfeeding or formula feeding normally unless the paediatrician provides different instructions. Parents should keep the baby warm and comfortable during collection.

The preferred collection time depends on the newborn-screening programme. Many programmes collect blood after the first 24–48 hours of life, while some routinely perform blood-spot screening between approximately 48 hours and five days after birth. Follow the paediatrician's or screening centre's specific instructions.

Blood collected too soon after birth may show a temporary physiological TSH rise and can increase the likelihood of an out-of-range result. If the baby must be tested early because of hospital discharge or another clinical reason, repeat screening may be recommended.

Inform the healthcare professional if the baby was premature, had a low birth weight, is critically unwell, has received a blood transfusion or is taking medicines. Also provide information about maternal thyroid disease, thyroid medicines, antithyroid treatment, iodine exposure and any family history of thyroid disorders.

During a blood-spot test, the heel is warmed and cleaned before a small sterile lancet is used to obtain several drops of blood. The drops are applied correctly to the screening card and allowed to dry before laboratory submission.

Normal Reporting Time

The Neonatal Screening (TSH) result is commonly available within approximately 2–5 working days after a suitable sample reaches the laboratory. The exact turnaround time may vary according to sample transport, collection quality, testing schedule and result verification.

Out-of-range or urgent results may be communicated earlier according to laboratory policy. Parents should ensure that their contact information is accurate and should promptly respond if the laboratory, hospital or paediatrician requests repeat or confirmatory testing.

Who Should Take This Test?

Neonatal thyroid screening is generally recommended for all newborn babies, even when they appear healthy and there is no family history of thyroid disease. Most affected babies cannot be identified reliably through appearance or physical examination alone.

Repeat testing may be recommended for babies tested very early, premature or low-birth-weight babies, critically ill newborns and babies whose first sample was inadequate, borderline or out of range. Repeat-testing rules vary according to the screening programme and clinical circumstances.

Babies born outside a hospital or discharged before screening should be taken to a paediatrician or appropriate screening centre promptly. Screening should not be delayed while waiting for symptoms to develop.

Detailed Information

TSH is released by the pituitary gland. When circulating thyroid-hormone concentrations are low, the pituitary normally increases TSH production to stimulate the thyroid. This feedback mechanism makes TSH a useful marker for screening for primary congenital hypothyroidism.

After birth, newborns experience a natural temporary increase in TSH. The concentration then decreases over the following days. For this reason, the baby's exact age at sample collection and the screening programme's age-specific cut-off are essential for interpretation.

An in-range screening result means that the result did not cross the programme's referral threshold. It substantially reduces the likelihood of primary congenital hypothyroidism but does not exclude every thyroid disorder or every case of central hypothyroidism.

An out-of-range result is not a confirmed diagnosis. The baby's doctor generally arranges urgent confirmatory venous tests, commonly serum TSH and free T4. Treatment decisions should be based on confirmatory results and paediatric evaluation.

Prematurity, neonatal illness, iodine deficiency or excess, maternal antibodies, maternal medicines and certain neonatal treatments may affect thyroid-test results. Some babies develop a delayed TSH rise and may therefore require repeat testing despite an initially acceptable result.

A sample may need to be repeated if the blood spots are insufficient, layered, contaminated, collected incorrectly or received too late. A repeat request usually reflects the need for a reliable sample and does not necessarily mean that the baby has thyroid disease.

Cut-off values differ according to the baby's age, sample type, analytical method and screening programme. Parents should not compare the result with an adult TSH range. Interpretation and follow-up should be managed by a paediatrician, neonatologist or paediatric endocrinologist.