Measurement of TSH levels in term neonates: A screening tool for congenital hypothyroidism

The primary aim of this study is the early detection of hypothyroidism in neonates. This prospective study was conducted to find normative values for thyroid stimulating hormone (TSH) in 5037 heel prick blood samples of term babies whose mothers were not on any thyroid medications.

All babies born at Sir Gangaram Hospital, New Delhi had a heel-prick blood sample collected at least 48 hours after birth, usually on Day 2–3, as part of the routine newborn screening program. TSH was measured using coated-tube immunoradiometric assay (IRMA). A full thyroid profile, viz, Serum FT3, FT4 and TSH was done at 7–10 days of age in all babies with TSH >20mIU/L.

The mean, median and standard deviation for the TSH values for the cohort were 7.319 mIU/L, 6.512 mIU/L and 9.240 respectively. 37 babies with TSH values >20mIU/L were given repeat tests. Hypothyroidism was confirmed in seven of these babies.

We conclude that a cut off value of TSH >20mIU/L is adequate for neonatal thyroid screening in Indian settings. Identification of infants suffering from congenital hypothyroidism is important as the condition causes irreversible brain damage if it is not diagnosed and treated soon after birth. The measurement of TSH in neonatal blood spots is a method of choice for screening for congenital hypothyroidism.