title: Comparison of two growth hormone stimulation tests and their cut-off limits in healthy adults at an outpatient clinic.
abstract: OBJECTIVE
  A peak GH less than 3 μg/L to insulin tolerance test (ITT) is commonly used as a threshold indicating severe adult GH deficiency (GHD). This cut-off is based on results obtained by polyclonal radioimmunoassays preferably under standard conditions at hospital. Our aim was to evaluate the validity of this cut-off limit using two currently used immunometric GH assays and to compare GH responses in the ITT and the GH releasing hormone + arginine (GHRH + ARG) test in healthy adults at our outpatient endocrine unit.
  
  
  METHODS
  ITT was performed on 73 subjects and the GHRH + ARG test on those 28 who showed insufficient response to the ITT.
  
  
  METHODS
  GH was measured by an immunofluorometric and immunochemiluminometric assay.
  
  
  RESULTS
  GH peak above 3 μg/L was observed in 56% of the healthy volunteers with adequate hypoglycemia in the ITT. Among the 28 subjects with a peak GH below 3 μg/L, only two overweight men had a GH peak response below the commonly used cut-off limit of 9.1 μg/L in the GHRH + ARG test.
  
  
  CONCLUSIONS
  Lean healthy adults could erroneously be classified as GH deficient by the ITT while their results in the GHRH + ARG test were normal. The GH results are highly dependent on the immunoassay used, but false positive results in the ITT are often obtained even if lower cutoff limits determined on the basis on the calibration of the GH assay are used. Confounding factors seemed to blunt the GH response to the ITT more than to the GHRH + ARG test at our outpatient clinic.
authors.affiliation: Department of Clinical Chemistry, Helsinki University Central Hospital, FI-00029 HUS, Finland.
authors.forename: Helene M
authors.initials: HM
authors.lastname: Markkanen
authors.forename: Tuula
authors.initials: T
authors.lastname: Pekkarinen
authors.forename: Matti J
authors.initials: MJ
authors.lastname: Välimäki
authors.forename: Henrik
authors.initials: H
authors.lastname: Alfthan
authors.forename: Esa
authors.initials: E
authors.lastname: Hämäläinen
authors.forename: Ulf-Håkan
authors.initials: UH
authors.lastname: Stenman
mesh_terms: D000328:Adult; D000554:Ambulatory Care Facilities; D001120:Arginine / Q000008:administration & dosage; D005260:Female; D013007:Growth Hormone-Releasing Hormone / Q000008:administration & dosage; D064368:Healthy Volunteers; D019382:Human Growth Hormone / Q000378:metabolism*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010901:Pituitary Function Tests / Q000379:methods* / Q000592:standards*; D012016:Reference Values; D055815:Young Adult
chemical_list: D019382:Human Growth Hormone; D013007:Growth Hormone-Releasing Hormone; D001120:Arginine
keywords: Adults; Diagnosis; GHRH+ARG; Growth hormone deficiency; ITT