Difficulties in selecting an appropriate neonatal thyroid stimulating hormone (TSH) screening threshold.
BACKGROUND
The UK Newborn Screening Programme Centre recommends that a blood spot thyroid stimulating hormone (TSH) cut-off of 10 mU/l is used to detect congenital hypothyroidism (CHT). As the value used varies from 5 to 10 mU/l, we examined the implications of altering this threshold.


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


RESULTS
148 of 65 446 infants (0.23%) had a first blood spot TSH >6.0 mU/l. 120 were term infants with 67 of these (0.1% of all infants tested) having a TSH between 6.1 and 10.0 mU/l and 53 a TSH >10.0 mU/l. Of the 67 term infants with a TSH between 6.1 and 10.0 mU/l on initial testing, four continued to have a TSH >6 mU/l. One with a TSH >10 mU/l and one infant with a TSH <10 mU/l on the second blood spot have been diagnosed with CHT. The survey of endocrinologists highlighted significant differences in practice.


CONCLUSIONS
A reduced threshold of 6 mU/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.
Korada
Srinivasa Murthy
SM
Institute of Health and Society, Newcastle University, Sir James Spence Institute, Royal Victoria Infi rmary, Newcastle upon Tyne, UK.
Pearce
Mark
M
Ward Platt
Martin P
MP
Avis
Enid
E
Turner
Steve
S
Wastell
Hilary
H
Cheetham
Tim
T
D015415:Biomarkers / Q000097:blood; D003409:Congenital Hypothyroidism / Q000175:diagnosis* / Q000188:drug therapy; D006801:Humans; D007231:Infant, Newborn / Q000097:blood*; D007234:Infant, Premature; D015997:Neonatal Screening / Q000379:methods*; D011364:Professional Practice / Q000706:statistics & numerical data; D012016:Reference Values; D012680:Sensitivity and Specificity; D013972:Thyrotropin / Q000097:blood*; D013974:Thyroxine / Q000627:therapeutic use; D006113:United Kingdom
D015415:Biomarkers; D013972:Thyrotropin; D013974:Thyroxine