Screening for congenital hypothyroidism: the value of retesting after four weeks in neonates with low and very low birth weight

Abstract

Objectives: Thyroid-stimulating hormone (TSH), normally a reliable screening test for congenital hypothyroidism (CH), may fail to detect cases among infants who have low and very low birth weight. The purpose of this study was to identify neonates with false-negative screening results. Setting: A province in Poland in which 3854 neonates had body weight ≤2500 g, between 1999 and 2001. Methods: TSH levels in blood on filter paper were measured in all neonates between the third and sixth days after birth, but were repeated in low and very low birth weight infants after four weeks of age. Results: The repeat test showed TSH levels ≥ 10 mIU/L in 19 of the 3854 low birth weight neonates. The final diagnosis in these neonates was permanent CH in two, transient CH in five, possible compensated CH in six and transient high TSH in six. Of the 19, 16 (84%) required iodine and/or thyroxine replacement therapy. Conclusions: In neonates with low and very low birth weight, normal TSH levels measured between the third and sixth day of life do not exclude thyroid dysfunction, but a repeat TSH measurement after the fourth week of life identifies the false-negative results. In our data, the prevalence of primary and secondary hypothyroidism (both permanent and transient) was about 0.5%.