title: Improved diagnosis of mild hypothyroidism using time-of-day normal ranges for thyrotropin.
abstract: OBJECTIVE
  To assess clinical utility of time-of-day-based thyrotropin (TSH) ranges.
  
  
  METHODS
  Ranges for TSH at 8 am, 4 pm, and am/pm TSH ratio were developed from prior data in 94 typical children (age, 5 to 18 years). Data for these values in 227 short children (1.5 to 18 years) were compared with those in typical children.
  
  
  RESULTS
  Short children included idiopathic short stature (ISS, n=153), central hypothyroidism (Central, n=42), and mild primary hypothyroidism (Primary, n=32), referred for evaluation of growth. In typical children, ISS, and Primary, 8 am TSH was greater than 4 pm TSH (P<.05). In Primary, 8 am TSH was greater than normal. Only 4 with Primary had elevated 4 pm TSH (using usual laboratory range of 0.5 to 4 mU/L). In contrast, only 63% of 4 pm TSHs in Primary were elevated. compared with 95% confidence limits in typical children. In Central, 8 am TSH and 4 pm TSH were within normal time-of-day range, and FT4 was in lowest one-third of normal. am/pm TSH ratio was less than 95% confidence limits in 76% of those with Central.
  
  
  CONCLUSIONS
  Either 8 am TSH or 4 pm TSH (compared with time-of-day normal range) can identify TSH elevation. Low am/pm TSH ratio (FT4 in lowest one-third of normal) confirms central hypothyroidism. Thus, time-of-day TSH ranges should be used for accurate diagnosis and more appropriate cost-effective treatment of mild hypothyroidism.
authors.affiliation: Cincinnati Children's Hospital Medical Center and University of Cincinnati, Cincinnati, OH 45242, USA. Susan.Rose@cchmc.org
authors.forename: Susan R
authors.initials: SR
authors.lastname: Rose
mesh_terms: D000293:Adolescent; D001827:Body Height; D002648:Child; D002675:Child, Preschool; D003362:Cost-Benefit Analysis; D005260:Female; D013006:Growth Hormone / Q000172:deficiency; D006801:Humans; D007037:Hypothyroidism / Q000097:blood* / Q000191:economics / Q000628:therapy; D008297:Male; D012016:Reference Values; D012720:Severity of Illness Index; D013972:Thyrotropin / Q000097:blood*; D013997:Time Factors; D016896:Treatment Outcome
chemical_list: D013972:Thyrotropin; D013006:Growth Hormone