77those neonates whose mother is receiving antithyroid drugs or with history of
previous baby with congenital hypothyroidism.- How to screen for congenital hypothyroidism?
Sample obtained by heel prick is preferred for neonatal screening of congenital
hypothyroidism. Following heel prick, blood drop is placed on specially designed
fi lter paper (Guthrie’s card), is allowed to dry (for 3h), and is sent to the labora-
tory. The common strategies employed for neonatal screening include “primary
TSH” or “primary T 4 –backup TSH.” However, the ideal screening strategy is
combined estimation of both T 4 and TSH. All newborns with abnormal screening
results should have a confi rmatory venous sample for FT 4 and TSH (Fig. 3.3 ).- Can cord blood be used for screening of congenital hypothyroidism?
Sample from umbilical cord can be used for screening of congenital hypothyroid-
ism. Cord blood contains mixed blood from both umbilical artery and veins and can
be smeared on fi lter paper (dried blood spot, DBS) or can be used after separation of
serum. Cord blood sampling is performed immediately after birth (prior to neonatal
surge which occurs after 30 min of birth), thereby reducing the number of false-
positive screening tests as a result of neonatal TSH surge. This also allows for early
discharge of healthy newborns and reduces the recall rate for confi rmation of thyroid
dysfunction. However, cord blood is not recommended for neonatal screening for
phenylketonuria (PKU) and congenital adrenal hyperplasia (CAH). This is because
sampling immediately after birth will result in underdiagnosis of phenylketonuria
and overdiagnosis (false positive) of congenital adrenal hyperplasia in newborns.Fig. 3.3 Neonatal screening card (Guthrie’s card). Note the fi lter paper marked with three circles,
where blood drop is to be placed for common screening of congenital hypothyroidism, congenital
adrenal hyperplasia, and phenylketonuria
3 Thyroid Disorders in Children