title: Growth hormone response during oral glucose tolerance test: the impact of assay method on the estimation of reference values in patients with acromegaly and in healthy controls, and the role of gender, age, and body mass index.
abstract: BACKGROUND
  Besides the measurement of IGF-I, GH suppression during an oral glucose tolerance test is recommended to assess the biochemical status in acromegaly. However, the development of highly sensitive and specific GH assays necessitates a critical reevaluation of criteria for diagnosis and follow-up of disease activity.
  
  
  OBJECTIVE
  Our objective was to evaluate the between-method discrepancies in GH determinations by different immunoassays considering further confounders like age, gender, and body mass index (BMI). DESIGN, SUBJECTS, AND METHODS: We measured GH during a 75-g oral glucose tolerance test in 46 acromegaly patients (18 controlled, 28 uncontrolled; 19 men; 31-63 yr; BMI 26.4 +/- 0.4 kg/m(2)) and 213 healthy subjects (66 men; 20-76 yr; BMI 30 +/- 0.5 kg/m(2)), using three different commercially available assays [Immulite (Diagnostic Products Corp., Los Angeles, CA), Nichols (Nichols Institute Diagnostika GmbH, Bad Vilbel, Germany), and Diagnostic Systems Laboratories (Sinsheim, Germany)] that were calibrated against the recently recommended GH standards.
  
  
  RESULTS
  Results from all assays strongly correlated (r = 0.8-0.996; P < 0.0001). However, the results obtained with the Immulite assay were, on average, 2.3-fold higher than those obtained with Nichols and 6-fold higher than those obtained with Diagnostic Systems Laboratories. Using cutoff limits of 1 microg/liter (Immulite) and 0.5 microg/liter (Nichols) identified 95% of patients with active disease and 78-80% of patients in remission. Basal and nadir GH levels were significantly higher in females than in males (Immulite 2.2 +/- 0.28 microg/liter vs. 0.73 +/- 0.15 microg/liter and 0.16 +/- 0.01 microg/liter vs. 0.08 +/- 0.01 microg/liter; P < 0.001, respectively). In multiple regression analysis, age, BMI, and gender were predictors for basal and nadir GH levels.
  
  
  CONCLUSIONS
  Postglucose GH-nadir values are assay, gender, age, and BMI specific, indicating the need of individual cutoff limits for each assay.
authors.affiliation: Department of Endocrinology, Diabetes and Nutrition, Charité-University Medicine Berlin, Campus Benjamin Franklin, Hindenburgdamm 30, 12200 Berlin, Germany. ayman.arafat@charite.de
authors.forename: Ayman M
authors.initials: AM
authors.lastname: Arafat
authors.forename: Matthias
authors.initials: M
authors.lastname: Möhlig
authors.forename: Martin O
authors.initials: MO
authors.lastname: Weickert
authors.forename: Frank H
authors.initials: FH
authors.lastname: Perschel
authors.forename: Johannes
authors.initials: J
authors.lastname: Purschwitz
authors.forename: Joachim
authors.initials: J
authors.lastname: Spranger
authors.forename: Christian J
authors.initials: CJ
authors.lastname: Strasburger
authors.forename: Christof
authors.initials: C
authors.lastname: Schöfl
authors.forename: Andreas F H
authors.initials: AF
authors.lastname: Pfeiffer
mesh_terms: D000172:Acromegaly / Q000188:drug therapy* / Q000378:metabolism; D000328:Adult; D000367:Age Factors; D000368:Aged; D015992:Body Mass Index; D002138:Calibration; D005260:Female; D005951:Glucose Tolerance Test; D019382:Human Growth Hormone / Q000097:blood / Q000627:therapeutic use*; D006801:Humans; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D012737:Sex Factors
chemical_list: D019382:Human Growth Hormone