title: The introduction of the IDS-iSYS total IGF-1 assay may have far-reaching consequences for diagnosis and treatment of GH deficiency.
abstract: BACKGROUND
  IGF-1 measurements are used for screening and monitoring GH deficiency (GHD) and acromegaly.
  
  
  OBJECTIVE
  Our objective was to study whether the introduction of the IDS-iSYS IGF-1 assay would lead to different clinical interpretations in GHD and acromegaly.
  
  
  METHODS
  In 106 GHD subjects and in 15 acromegalic subjects visiting our university hospital, total IGF-1 levels were measured before and during therapy by using the Immulite (IM) assay and IDS-iSYS (ID) assay. Z-scores were calculated by using assay-specific age-specific normative range values. All treatment decisions were based upon results obtained by the IM assay.
  
  
  RESULTS
  In GHD subjects, absolute IGF-1 concentrations differed significantly between both IGF-1 assays before treatment (P < .001) but not during GH treatment (P = .32), and mean Z-scores for IGF-1 differed significantly before starting (IM, -2.23, vs ID, -1.43; P < .001) and during GH treatment (IM, -0.60, vs ID, +0.21; P < .001). In acromegalic subjects, absolute IGF-1 concentrations did not differ between both IGF-1 assays before treatment (P = .18) but were significantly different during treatment (P = 0.009), and mean Z-scores for IGF-1 were not different before starting (IM, 10.93, vs ID, 10.78; P = .41) or during treatment (IM, 3.60, vs ID, 3.18; P = .23).
  
  
  CONCLUSIONS
  In GHD subjects, mean IGF-1 Z-scores significantly differed when measured by the IM assay compared with the ID assay irrespective of treatment. In contrast, in acromegaly, mean IGF-1 Z-scores did not differ significantly between both assays. Our study suggests that replacement of the IM assay by the ID assay may have far-reaching consequences for the clinical diagnosis and treatment of GHD.
authors.affiliation: Department of Internal Medicine, Division of Endocrinology, Erasmus Medical Center, 3015 CE Rotterdam, The Netherlands.
authors.forename: A J
authors.initials: AJ
authors.lastname: Varewijck
authors.forename: S W J
authors.initials: SW
authors.lastname: Lamberts
authors.forename: A J
authors.initials: AJ
authors.lastname: van der Lely
authors.forename: S J C M M
authors.initials: SJ
authors.lastname: Neggers
authors.forename: L J
authors.initials: LJ
authors.lastname: Hofland
authors.forename: J A M J L
authors.initials: JA
authors.lastname: Janssen
mesh_terms: D000172:Acromegaly / Q000097:blood / Q000175:diagnosis* / Q000628:therapy; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D004393:Dwarfism, Pituitary / Q000097:blood / Q000175:diagnosis* / Q000628:therapy; D005260:Female; D006801:Humans; D007118:Immunoassay; D007334:Insulin-Like Growth Factor I / Q000032:analysis*; D008163:Luminescent Measurements; D008297:Male; D008875:Middle Aged; D055815:Young Adult
chemical_list: D007334:Insulin-Like Growth Factor I