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. Māori 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.