NBS - Congenital Hypothyroidism (TSH)

Congenital hypothyroidism is suggested by an elevated TSH—commonly a newborn screening dried‑blood spot TSH >20 mIU/L or a venous TSH >10 mIU/L—often accompanied by low free T4. Cutoffs vary by program and age, so abnormal screening results require prompt repeat/confirmatory testing and pediatric endocrinology follow‑up. Immediate levothyroxine treatment is started when diagnosis is confirmed to prevent neurodevelopmental impairment.

NBS for hypothyroidism is newborn screening using a heel‑prick blood spot to measure TSH and/or T4 to detect congenital hypothyroidism early. Performed usually 2–5 days after birth, it flags infants needing confirmatory serum testing and urgent levothyroxine treatment. Timely diagnosis and treatment prevent intellectual disability, growth failure, and long‑term developmental and metabolic complications.

Primary congenital hypothyroidism is characterized by low free thyroxine (free T4) below age‑specific reference ranges with markedly elevated thyroid‑stimulating hormone (TSH). Newborn screening commonly flags TSH >20 mIU/L within the first week; confirmatory testing typically shows TSH >10–40 mIU/L (frequently >20 mIU/L) concurrent with low free T4, indicating primary thyroid failure.

TSH and T4 newborn screening detects congenital hypothyroidism by measuring thyroid-stimulating hormone (TSH) and thyroxine (T4) from a heel-prick blood sample taken shortly after birth. It identifies low thyroid hormone production that can cause growth and developmental delays. Early detection allows prompt confirmatory testing and treatment with levothyroxine to prevent intellectual disability and support normal growth.

Congenital hypothyroidism is confirmed after an abnormal newborn screen (elevated TSH and/or low T4) by prompt venous serum testing: markedly raised TSH with low free T4 establishes the diagnosis. Repeat tests may be done to verify results. Thyroid imaging (ultrasound or radionuclide scan) and further tests (antibody or genetic studies) can determine the cause; treatment is started immediately.

Alarming TSH levels are generally >10 mIU/L (suggesting overt hypothyroidism) or <0.1 mIU/L (suggesting hyperthyroidism). Both warrant prompt medical review—especially with symptoms like extreme fatigue, weight change, palpitations, fainting, swelling, or altered consciousness. Pregnant women and people with heart disease need earlier evaluation; lab ranges and targets vary, so follow your clinician’s guidance.