Neonatal plasma TSH – estimated upper reference intervals for diagnosis and follow up of congenital hypothyroidism

Abstract

Age- and method-dependent plasma TSH reference intervals are essential for the diagnosis and management of congenital hypothyroidism. However, accurate reference intervals for plasma TSH have not been adequately defined due to the difficulties in obtaining samples from a healthy paediatric population. To overcome the difficulties in generating such intervals we estimated method-dependent plasma TSH upper-reference intervals by determining the blood spot TSH upper-reference interval from newborn blood spot TSH screening data (N = 10,697) and then derived method-dependent conversion factors for blood spot TSH to plasma TSH concentration from paired-blood spot and plasma TSH measurements. The upper reference interval for blood spot TSH of 3.04 mU/L was obtained from the 97.5th centile of the selected data. Using experimentally-derived conversion factors, estimates of plasma TSH upper reference intervals of 7.6, 6.3, 7.3, 8.3 and 6.5 mU/L were obtained for the Siemens Centaur, Abbott Architect, Roche Elecsys E170, Siemens Immulite 2000 and Beckman access HYPERsensitive TSH assays respectively. These estimated method-dependent plasma TSH upper reference intervals will be of great practical use to clinicians to diagnose and to follow up infants found to have increased blood spot TSH concentrations identified by Newborn Screening programmes.

Key Words::

• Congenital hypothyroidism
• thyroid stimulating hormone (TSH)
• reference ranges

Acknowledgements

We thank Robert Henley, Dr. Don Bradley, Dr. Rhys John, Dr. Catherine Bailey and Dr. Andrew Fielding and the All Wales Clinical Biochemistry Audit Group for their advice and support and the clinical biochemists and chemical pathologists throughout Wales who responded to the audit questionnaire. We thank Dr. Rebekah Price, Helen Owen, Dr Laith Al-Sweedan, Dr. Karen Poyser, Steven Palfrey, L. Pritchard, Stephen Bevan and Mike Hallworth for their contribution towards audit and laboratory data collection.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.