Defining the Newborn Blood Spot Screening Reference Interval for TSH: Impact of Ethnicity

CONTEXT: There is variability in the congenital hypothyroidism (CH) newborn screening TSH cutoff across the United Kingdom. OBJECTIVE: To determine the influences of year, gender, and ethnicity on screening variability and examine whether there is an optimal operational TSH cutoff. DESIGN AND SETTING: Single center, retrospective population study using blood spot TSH cards received by the Great Ormond Street Hospital Screening Laboratory between 2006 and 2012. PATIENTS: A total of 824 588 newborn screening blood spot TSH cards. INTERVENTION: Blood spot TSH results were recorded with demographic data including the Ethnic Category Code. MAIN OUTCOME MEASURES: The proportions of samples exceeding different TSH cutoffs, ranked by ethnicity. RESULTS: The proportion of samples exceeding the TSH cutoff increased over time, with the cutoff at 4 mU/L, but not at 6 mU/L. There was a consistent trend with ethnicity, irrespective of cutoff, with the odds ratio of exceeding the TSH cutoff lowest (∼1.0) in White babies, higher in Pakistani and Bangladeshi (>2.0), and highest in Chinese (>3.5). CONCLUSIONS: The blood spot TSH screening data demonstrate a clear ranking according to ethnicity for differences in mean TSH. This suggests that there may be ethnic differences in thyroid physiology. Ethnic diversity within populations needs to be considered when establishing and interpreting screening TSH cutoffs.