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Difficulties in selecting an appropriate Neonatal TSH screening threshold
  1. Srinivasa Murthy Korada (srinivasa.korada{at}ncl.ac.uk)
  1. University of Newcastle Upon Tyne, United Kingdom
    1. Mark Pearce (m.s.pearce{at}ncl.ac.uk)
    1. University of Newcastle Upon Tyne, United Kingdom
      1. Martin P Ward Platt (m.p.ward-platt{at}ncl.ac.uk)
      1. Neonatal Service (Ward 35), United Kingdom
        1. Enid Avis (enid.avis{at}nuth.nhs.uk)
        1. University of Newcastle Upon Tyne, United Kingdom
          1. Steve Turner (steve.turner{at}nuth.nhs.uk)
          1. Royal Victoria Infirmary, United Kingdom
            1. Hilary Wastell (hilary.wastell{at}nuth.nhs.uk)
            1. Royal Victoria Infirmary, United Kingdom
              1. Tim Cheetham (tim.cheetham{at}nuth.nhs.uk)
              1. University of Newcastle Upon Tyne, United Kingdom

                Abstract

                Background: The UK Newborn Screening Program Centre recommend that a blood-spot TSH cut-off of 10mU/l is used to detect congenital hypothyroidism. The value used varies from 5-10mU/l and so we examined the implications of altering this threshold.

                Methods: Our regional blood spot TSH cut-off is 6mU/l. Positive or suspected cases were defined as a TSH >6mU/l throughout the study period (1/4/2005 to 1/3/2007). All term infants (>35 weeks) whose first TSH was 6-20mU/l had a second TSH measured. The biochemical details of infants with a TSH between 6.1-10.0mU/l and then >6mU/l on second sampling were sent to Paediatric Endocrinologists to determine approaches to management.

                Results: 148 of 65446 infants (0.23%) had a first blood spot TSH >6.0mU/l. 120 were term infants with 67 of these (0.1% of all infants tested) having a TSH between 6.1-10.0mU/l and 53 a TSH >10.0mU/l. Of the 67 term infants with a TSH between 6.1-10.0mU/l on initial testing, 4 continued to have a TSH >6mU/l. One with a TSH greater than 10 mU/l and 1 infant with a TSH <10mU/l on the second blood spot have been diagnosed with congenital hypothyroidism. The survey of endocrinologists highlighted significant differences in practice.

                Conclusions: A reduced threshold of 6mU/l will increase the number of false positive ‘term’ infants by 126% but abnormalities of thyroid function requiring treatment will be detected. We suspect that the additional expense involved in setting a lower threshold is justified.

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