Screening Blind Spot: Missing Preterm Infants in the Detection of Congenital Hypothyroidism.

Congenital hypothyroidism (CH) is a critical condition in infancy where early detection is vital for optimal development. This study aimed to evaluate the sensitivity of Aotearoa New Zealand's Newborn Metabolic Screening "Low Birth Weight" protocol for detecting CH in preterm infants. A 10-year audit was conducted on 2935 preterm infants (<2000 g or ≤34 weeks gestation) screened within NICUs or SCBUs in the Auckland region. The study assessed both screen-detected and clinically detected cases of CH. Data were collected from screening and clinical records to evaluate the sensitivity and reliability of the current protocol. The audit identified 19 cases of primary CH, with a 1:154 incidence. Thirteen cases met the criteria for inclusion in the audit. Just over half of the eligible cases (7/13) were screen-detected, while the remaining were detected clinically, suggesting limitations in screening sensitivity. The analysis revealed that the protocol missed permanent as well as transient cases, and that biochemical severity was not predictive of permanence. A revised screening protocol was developed and commenced in July 2024.