Investigation

Routine screening should be done in all infants.

• in UK, filter paper blood spot TSH measurement is used for screening - the TSH is high and diagnostic in primary hypothyroidism but normal or low in secondary hypothyroidism
  • the test is restricted to specialist centers
  • to avoid false positive results (since increased TSH levels are seen up to 24h following birth) the sample should be taken at least 48 hours after birth (within 2-8 day ) (1)
• confirmatory examinations of congenital hypothyroidism:
  • should be done immediately after the TSH screening test (around 2 weeks after birth)
  • measure serum TSH and free T4 levels
    • increased serum TSH and a low free T4 or total free T4 indicates the diagnosis of primary hypothyroidism (2)
• radiology may reveal delay in ossification and fragmentation of the epiphyses
• radioactive marker uptake may be used to locate ectopic glands

Note:

• in preterm infants or acutely ill term infants with primary hypothyroidism, increased TSH levels may not be detected during the first screening test
  • such infants are required to undergo a routine second screening test which will identify these infants with "delayed TSH rise"
  • present in approximately 1:18,000 newborns (2)

Reference:

• (1) Association for Clinical Biochemistry (ACB), British Thyroid Association (BTA), British Thyroid Foundation (BTF) 2006. UK guidelines for the use of thyroid function tests
• (2) Rastogi MV, LaFranchi SH. Congenital hypothyroidism. Orphanet J Rare Dis. 2010;5:17