Objective To evaluate the effectiveness of four dried blood spot testing protocols used in newborn screening for congenital hypothyroidism (CH) among newborns transferred to the neonatal intensive care unit (NICU).

Design, setting and patients Michigan newborns transferred to the NICU from 1998 to 2011 and screened for CH are included in this population-based retrospective cohort study.

Main outcome measures Screening performance metrics are computed and logistic regression is used to test for differences in the likelihood of detection across four periods characterised by different testing protocols.

Results Primary thyrotropin (TSH) plus retest at 30 days of life or discharge achieved the greatest detection rate (2.6: 1000 births screened). The odds of detection was also significantly greater in this period compared with the tandem thyroxine (T4) and TSH testing period and separately compared with TSH testing alone, adjusted for birth weight, sex and race (OR 1.5; CI 1.0 to 2.2; p=0.046, and OR 2.2; CI 1.5 to 3.4, respectively). Approximately half of the cases detected during primary TSH plus serial testing periods were identified by retest.

Conclusions Primary TSH testing programmes that do not incorporate serial screening may fail to identify approximately half of newborns with congenital thyroid hormone deficiency transferred to the NICU. Tandem T4 and TSH testing programmes also likely miss cases who otherwise would receive treatment if serial testing were conducted. Further research is necessary to determine the optimal newborn screening protocol for CH; strategies combining tandem T4 and TSH with serial testing conditional on birthweight may be useful.