title: Human growth hormone (GH) immunoassay: standardization and clinical implications.
abstract: BACKGROUND
  The poor comparability of growth hormone (GH) results obtained using commercially available methods, is partly due to standard preparations used in calibration. The system relies on the use of the International Reference Preparation (IRP) international standard (IS) 80/505, of human pituitary origin, containing all GH isoforms. Recently, a 22K recombinant GH isoform IRP IS 98/574 was commercialized. Our aim was to evaluate the influence of both calibrators on GH results.
  
  
  METHODS
  GH concentration in 97 serum samples from children undergoing a growth hormone releasing hormone+arginine stimulation test was measured using Siemens IMMULITE electro-chemiluminescence method, calibrated with both IS 80/505 and IS 98/574 (GRH Growth hormone-Recombinant 98/574-kit).
  
  
  RESULTS
  Comparison of our results obtained with the two sets of calibrators showed good correlation, although we found higher percentage variation (var%) than that stated by Siemens. The mean var% value was confirmed when all results were sub-divided into subgroups based on both high and low GH concentrations.
  
  
  CONCLUSIONS
  Since the GH assay is influenced by a variety of binding proteins, isoforms and conversion factors, standardization of the assay is strongly required. In Italy, the Agenzia Italiana del Farmaco 39 note provides GH laboratory values which are useful for therapy. On the basis of our results, we therefore propose to adjourn these GH values in order to ensure better management of patients with GH-related disorders.
authors.affiliation: Institute of Biochemistry and Clinical Biochemistry, Catholic University School of Medicine, Rome, Italy. ccarrozza@rm.unicatt.it
authors.forename: Cinzia
authors.initials: C
authors.lastname: Carrozza
authors.forename: Rosa
authors.initials: R
authors.lastname: Lapolla
authors.forename: Giulia
authors.initials: G
authors.lastname: Canu
authors.forename: Francesca
authors.initials: F
authors.lastname: Annunziata
authors.forename: Eleonora
authors.initials: E
authors.lastname: Torti
authors.forename: Silvia
authors.initials: S
authors.lastname: Baroni
authors.forename: Cecilia
authors.initials: C
authors.lastname: Zuppi
mesh_terms: D002138:Calibration; D002648:Child; D019382:Human Growth Hormone / Q000097:blood* / Q000276:immunology; D006801:Humans; D007118:Immunoassay / Q000295:instrumentation / Q000592:standards*; D038622:Internationality; D012015:Reference Standards
chemical_list: D019382:Human Growth Hormone