ESPE Abstracts

Background: Approximately one baby in 2000-3000 is born with congenital hypothyroidism (CHT). Newborn screening of CHT is conducted in different countries by the measurement of either thyroid stimulating hormone (TSH) of free thyroxine (FT4) or both. Whereas most Western countries screened CHT by using a blood spot collected on day 3 to 5 of life, some countries' programmes measure umbilical cord blood TSH or FT4 for the screening of CHT. In our maternity hospital, cord serum TSH concentration is routinely measured for all newborn babies, and FT4 is reflex-tested in the same cord serum specimen if cord TSH concentration is 23.0 mIU/L or above, or below 1.0 mIU/L.

Methodology: Umbilical cord serum TSH and FT4 concentrations were measured using automated immunoassays (Abbott Architect). Cord TSH (with or without FT4 results) generated from this screening programme between January 2016 and December 2017 (24 months) were retrospectively reviewed.

Results and Discussion: Within the 24-month period, 11130 females (47.9%) and 12127 males (52.1%) were screened for CHT. Cord TSH concentrations ranged from <0.01 to 482 mIU/L. Median TSH in males (4.91 mIU/L; IQR, 3.70 – 6.77 mIU/L) was slightly higher than median TSH in females (4.61 mIU/L; IQR, 3.47 – 6.28 mIU/L) (P<0.0001).

There were 22448 cord TSH results (96.5% of total) falling within the local TSH reference interval (2.20 – 24.99 mIU/L). Among those TSH results outside the local TSH reference interval, 742 results (3.2% of total) were below 2.20 mIU/L, whereas 67 results (0.3% of total) were 25.0 mIU/L or above. The vast majority of TSH results (88.6% of total) were between 2.20 and 9.99 mIU/L.

Approximately 0.5% of specimens underwent reflex measurement of free T4 concentration (when cord TSH concentration was 23.0 mIU/L or above, or below 1.0 mIU/L). The workload of FT4 reflex-testing is not considered onerous for laboratory resources. Among those 105 cord serum specimens with TSH concentration 23.0 mIU/L or above, their FT4 concentrations ranged from 9.0 to 20.6 pmol/L (local FT4 reference interval, 12.5 – 27.5 pmol/L). Median cord FT4 concentration was 12.7 pmol/L (IQR, 11.8 – 14.1 pmol/L) in newborn babies with cord TSH concentration 23.0 mIU/L or above. Correlation by linear regression both between FT4 and TSH concentrations and between FT4 and log(10) TSH concentrations was relatively weak (r-square, 0.073 and 0.109 respectively).