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Hence, cord blood sampling is not preferred for neonatal screening of congenital

hypothyroidism in regions where neonatal screening for PKU and CAH is routinely

performed, as screening for all these disorders (PKU, CAH, and CH) can be done

from a single sample obtained from heel prick after 2–3 days of life. However, cord

blood is an alternative to heel prick sampling for neonatal screening of congenital

hypothyroidism in regions with low prevalence of phenylketonuria and CAH.

8. What are the merits and demerits of different strategies in neonatal screening
   program for congenital hypothyroidism?
   The commonly used strategies for neonatal screening of congenital hypothy-
   roidism include “primary TSH” and “primary T 4 –backup TSH.” TSH is the
   most sensitive test for the diagnosis of primary congenital hypothyroidism;
   however, a primary TSH strategy will miss central hypothyroidism and neo-
   nates with hypothyroxinemia with delayed TSH rise (which is common in
   newborns with low birth weight). In addition, congenital thyroxine-binding
   globulin defi ciency will also be missed which may not be of clinical rele-
   vance. The primary T 4 approach can diagnose secondary hypothyroidism
   and thyroxine-binding globulin defi ciency; however the primary T 4 strategy
   will miss compensated hypothyroidism (e.g., in ectopic thyroid tissue) and
   subclinical hypothyroidism. Both these approaches require a recall rate of
   approximately 0.05 % and may miss 3–5 % patients with congenital hypo-
   thyroidism. This may be due to improper sample collection, technical diffi -
   culties with assays, and immaturity of hypothalamo–pituitary–thyroid axis.
   “Simultaneous T 4 and TSH”-based neonatal screening is the ideal screening
   strategy; however, the cost- effectiveness of this approach has not been
   proven. The table given below shows the incidence of various etiologies of
   congenital hypothyroidism and merits and demerits of screening with vari-
   ous approaches.

Cause Incidence

Primary

TSH

Primary

T 4 –backup TSH

Simultaneous

T 4 and TSH

Primary

hypothyroidism

1 in 2500 Good Good Excellent

Secondary

hypothyroidism

1 in 16,000–1 in 100,000 No Few cases a Few cases a

Subclinical

hypothyroidism

1 in 30,000 Yes No Yes

a Free T 4 is required for diagnosis as total T 4 can be normal in newborn with secondary hypothy-
roidism because of increased TBG as a result of transplacental transfer of estradiol

9. How to interpret the results of neonatal screening program?

The primary TSH-based approach for neonatal screening program and further

management are depicted in the fi gure given below (Fig. 3.4 ).

3 Thyroid Disorders in Children