Evaluation of the revised New Zealand national newborn screening protocol for congenital hypothyroidism.

Objective: The aim of this study was to assess the performance of the revised New Zealand (NZ) newborn screening TSH cut-offs for congenital hypothyroidism (CHT).

Methods: Screening data over 24 months were obtained from the NZ newborn metabolic screening programme, which utilizes a 2-tier system of direct clinical referral for infants with markedly elevated TSH, and second samples from those with mild TSH elevation. We evaluated the impact of a reduced TSH threshold (50 to 30 mIU/l blood) for direct notification and a lower cut-off (15 to 8 mIU/l blood) applied to second samples and babies older than 14 days.

Results: In 2013 and 2014, 117 528 infants underwent newborn screening for CHT. Fifty-two CHT cases were identified by screening (47 general newborn population, five repeat testing in low-birth-weight infants) and one case was missed. Thirty-two infants with screening TSH ≥30 mIU/l were directly referred at a median of 9 days (5-14) and 15 with TSH 15-29 mIU/l were referred after a second sample at a median of 20 days (9-52, P < 0·001). All directly referred infants were confirmed as CHT cases with no earlier referrals as a result of the reduced threshold. The lower TSH cut-off applied to second samples lead to the identification of six extra cases of CHT (15% increase) from seven extra clinical referrals.

Conclusions: The NZ screening programme achieved a 15% increase in CHT case detection for minimal increase in workload or anxiety for families of healthy infants. A further decrease in the threshold for direct referral may allow earlier diagnoses.