Perinatology.  2020 Dec;31(4):166-171. 10.14734/PN.2020.31.4.166.

Correlation between Capillary Blood-spotted Filter Paper Thyrotropin Results and Serum Thyroid Function Tests in Premature Neonates

• Ahn MB
• Kim SH
• Cho WK
• Cho KS
• Kim SY
• Suh BK
• Jung MH

• KMID: 2510388
• DOI: http://doi.org/10.14734/PN.2020.31.4.166

Abstract

Objective
The interpretation of thyroid function test results in preterm infants is affected by various conditions. Neither a definite thyrotropin cut-off nor intercurrent conditions have been clearly deter mined for premature neonates. This study aimed to determine the specific considerations required in the interpretation of capillary blood thyrotropin concentration by comparing it to serum thyrotropin when screening for congenital hypothyroidism in preterm neonates.
Methods
A retrospective review was performed on 57 premature newborns who were screened for thyroid function test. The comparison of thyrotropin measured by two different methods, dried capil lary blood-spotted filter paper using an immunofluorometric assay and serum radioimmunoassay, was performed. Clinical and biochemical factors affecting the difference between the two methods were investigated.
Results
Filter paper thyrotropin concentration showed a positive correlation with the serum thyro tropin concentration. In total, 50.9% of premature neonates had a difference in the concentration ≥3.0 mIU/L between the methods. In these subjects, the serum thyrotropin concentration was higher, whereas other factors, such as maternal factors, neonatal anthropometric parameters, Apgar score, and corrected age, were not different when compared to that in subjects with a difference of <3.0 mIU/L.
Conclusion
The filter paper thyrotropin concentration differed from the serum level in a substantial portion of premature neonates, and the degree of deviation may be affected by the serum thyrotropin concentration and gestational age at birth. Further investigations and longitudinal studies are war ranted to establish clinical consensus guidelines for hypothyroidism screening in preterm neonates.

Keyword

Congenital hypothyroidism; Dried blood spot testing; Premature birth; Thyrotropin