Newborn screening of premature infants for congenital hypothyroidism (CH) may initially be normal despite the presence of thyroid pathology and therefore repeat TSH screening is required. The 2012 revised UK Newborn Screening guidelines for premature infants state that infants born <32 weeks gestation require a repeat TSH bloodspot at 28 days postnatal age or discharge home, whichever is earlier. Prior to this, repeat testing was required at 36 weeks corrected gestation for all pre-term infants born <36 weeks.
Method: We audited pre-term referrals to our centre pre and post guideline changes. Data were collected for gestational age, birth weight, bloodspot TSH concentration, venous free T4 and TSH, age of referral and need for levothyroxine therapy.
Results: In babies born <32 weeks, we found an increase in referrals in the 1 year post policy change (17 referrals in 20122013 compared with an average of five referrals per year between April 2006 and 2012). The increase in referrals were mainly in infants with TSH concentrations <20 mU/l. 47 pre-term babies born at 3236 weeks gestation were referred between 2006 and 2012. 14/47 had a venous TSH>20 mU/l and low free T4 concentrations and were commenced on levothyroxine.
Discussion: Changes to the newborn screening of premature infants has increased the number of borderline referrals born at <32 weeks. Repeat screening at 28 days may detect a TSH surge that has resolved when repeat screening occurs later at 36 weeks. These false positive referrals need to be balanced by the potential neurodevelopmental benefit of earlier commencement of levothyroxine for those babies with confirmed CH. The new standards no longer require repeat screening in babies born at 3236 weeks gestation and would have missed the 14 babies requiring levothyroxine treatment prior to the change in standards.
13 Nov 2013
British Society for Paediatric Endocrinology and Diabetes