title: Serum human chorionic gonadotropin concentrations greater than 400,000 IU/L are invariably associated with suppressed serum thyrotropin concentrations.
abstract: BACKGROUND
  During pregnancy, when human chorionic gonadotropin (hCG) concentrations are highest, there is a transient suppression of serum thyrotropin (TSH). In normal pregnancy, TSH concentrations generally remain within nonpregnant reference intervals; however, in some patients TSH is suppressed. Here we sought to extend previous studies to examine the relationship between very high serum concentrations of hCG (>200,000 IU/L) and the thyroid hormones TSH and free thyroxine (FT(4)). The objective of this study was to determine: 1) if there is an hCG concentration above which TSH concentrations are suppressed (< or =0.2 microIU/mL); 2) how thyroid hormone concentrations change in response to changes in hCG concentrations; and 3) the clinical symptoms in patients with such extremely elevated hCG concentrations.
  
  
  METHODS
  Residual specimens sent to the laboratories for physician-ordered hCG testing were utilized. Over 26 months, 15,597 physician-ordered hCG tests were performed. Sixty-nine specimens from 63 women with hCG concentrations >200,000 IU/L were identified, and TSH and FT(4) concentrations were measured. Medical records were reviewed for clinical information.
  
  
  RESULTS
  Thirty-seven percent of subjects had hyperemesis gravidarum (HG) and 19% had gestational trophoblastic disease (GTD). TSH was suppressed (< or =0.2 microIU/mL) in 67% of the specimens with hCG concentrations >200,000 IU/L and 100% of specimens with hCG concentrations >400,000 IU/L. FT(4) concentrations were elevated above the reference interval (1.8 ng/dL) in 32% of specimens with hCG concentrations >200,000 IU/L and in 80% of specimens with hCG concentrations >400,000 IU/L. Only four subjects had documented signs of hyperthyroidism. Women with GTD had a median hCG concentration twofold higher than women with HG and a median TSH concentration one half that of women with HG.
  
  
  CONCLUSIONS
  1) At hCG concentrations >400,000 IU/L, TSH is consistently suppressed; 2) serum FT(4) and TSH respond to changes in serum hCG concentrations; and 3) most patients with hCG concentrations >200,000 IU/L lack overt hyperthyroid symptoms.
authors.affiliation: Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
authors.forename: Christina M
authors.initials: CM
authors.lastname: Lockwood
authors.forename: David G
authors.initials: DG
authors.lastname: Grenache
authors.forename: Ann M
authors.initials: AM
authors.lastname: Gronowski
mesh_terms: D006063:Chorionic Gonadotropin / Q000097:blood*; D015331:Cohort Studies; D005260:Female; D005865:Gestational Age; D031901:Gestational Trophoblastic Disease / Q000097:blood; D006801:Humans; D006939:Hyperemesis Gravidarum / Q000097:blood; D006980:Hyperthyroidism / Q000097:blood; D011247:Pregnancy; D012016:Reference Values; D013960:Thyroid Function Tests; D013972:Thyrotropin / Q000097:blood*; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood
chemical_list: D006063:Chorionic Gonadotropin; D014284:Triiodothyronine; D013972:Thyrotropin; D013974:Thyroxine