Introduction: Revised UK neonatal screening guidelines recommend that a second TSH blood sample be taken when preterm infants reach a postmenstrual age of 36 weeks.
Methods: We examined the results of a regional screening programme to see whether a rise in TSH concentrations was observed in some preterm infants between the first sample taken around 5 days after delivery and the second sample taken at around 36 weeks. Whole blood TSH levels from preterm infants born over a 2 year period (April 2005 - March 2007) were assessed and the number of infants with a fall or rise to values below or above the local screening threshold (6mU/l) determined.
Results: Baseline TSH samples were obtained from 2238 preterm infants (median gestational age 32w, range 21-35) with second samples obtained from 2039 (median gestational 32w, range 23-35). In 19 infants TSH levels fell from above to below the screening threshold and in 5 infants values rose from below the screening threshold to between 6 and 10 mU/l. However TSH values fell to less than 6mU/l on a further blood spot in 4 of these infants and the remaining infant had a serum TSH of 6.8mU/l. 3 infants had raised TSH values on both occasions with unequivocal hypothyroidism (serum TSH > 80 mU/l). The initial TSH on one of these infants was between 6 and 10mU/l.
Conclusions: No infant with a normal TSH on first sampling had a TSH that rose above 10mUl on second sampling and none with a normal TSH on first screening are on long term thyroxine treatment. Our study suggests that a second sample may not be necessary with a screening threshold of 6mU/l.
- Congenital hypothyroidism
- preterm infants
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