In reply: The methods used for blood sample collection and analysis remained unchanged during our data collection period. One source of thyroid-stimulating hormone (TSH) calibrators and reagents was used over the study period by a single laboratory covering all of Victoria. Material from the United States Centers for Disease Control and Prevention was used for external quality assurance, ensuring that the results were in agreement with those of other laboratories. The per cent coefficient of variation over the period ranged from 10% to 20%.
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