The impact of demographic factors on newborn TSH levels and congenital hypothyroidism screening

Context Optimal newborn screening thyroid-stimulating hormone (TSH) cut-offs are contentious. Analysis of demographic factors that impact screen TSH levels may help explain international variance and provide guidance to screening programmes. Objective To determine the influence of demographic factors on newborn screening TSH levels and screening performance parameters. Design and Setting National, retrospective population study using blood spot TSH cards from the New Zealand newborn screening programme in 2010-2015. Patients 325 685 blood spot cards. Main Outcome Measures Likelihood of exceeding specific TSH thresholds (TSH >= 5, >= 10 and >= 15 mIU/L) and group-specific screening performance parameters. Results The likelihood of high TSH levels differed between ethnic groups. Pacific Island infants were more than twice as likely to have high-normal TSH levels (>= 5 and >= 10 mIU/L) and nearly twice as likely to have a positive screen (>= 15 mIU/L) as New Zealand Europeans. Maori or Chinese ethnicity, male sex, younger gestational age and greater socio-economic deprivation scores were also associated with high-normal TSH levels. At a TSH threshold >= 15 mIU/L, screening sensitivity was lowest (88.89% vs 95.83% overall) and PPV greatest (88.89% vs 62.84%) amongst Asian infants. Early samples were more than three times as likely to reach the screen-positive threshold and more likely to yield a false-positive result (PPV 20.00% vs 68.87%, P = 0.004). Conclusions Newborn TSH levels are impacted by a number of demographic variables, particularly ethnicity and age at sample collection. Screening performance may be improved through the use of targeted thresholds.