title: Evaluation of Variables Influencing the Measurement of Insulin-like Growth Factor-1.
abstract: OBJECTIVE
  Our aim was to identify the frequency and possible clinical and analytical factors leading to "falsely" elevated insulin-like growth factor-1 (IGF-1).
  
  
  METHODS
  We performed a retrospective review of patients with IGF-1 concentrations above the reference interval. They were selected from a database of patients who had consecutive IGF-1 measurements between the years 2007-2010.
  
  
  RESULTS
  Out of 2,747 unique patients, 117 (4%) were found to have IGF-1 concentrations above the reference interval that were considered false-positives following a review of the clinical data. There was no relationship between the percentage of increase in IGF-1 and age, sex, body mass index (BMI), comorbidities, medication use, gonadal status, baseline growth hormone (GH), or insulin-like growth factor binding protein-3 (IGFBP-3) concentrations. An abnormal IGF-1 concentration led to performance of an oral glucose tolerance test (OGTT) for GH suppression in 21 of 117 patients (18%) and repeat IGF-1 measurements in 52 patients (44%). In 34 of 52 patients (65%) with a median follow-up of 36 months, the subsequent IGF-1 concentration was within the reference interval.
  
  
  CONCLUSIONS
  Discovery of "falsely" elevated IGF-1 concentrations may lead to unnecessary testing and physician visits. Although the cause of the "falsely" elevated IGF-1 concentrations during the study period remains to be elucidated, it appears they are caused by a combination of high biological variability and method-specific assay performance issues. Clinicians should consider retesting patients with potentially spurious IGF-1 elevations after some time interval before embarking on more extensive investigations.
authors: Division of Endocrinology, Metabolism and Nutrition, Department of Medicine, Mayo Clinic, Rochester, Minnesota.
authors: Irina
authors: I
authors: Bancos
authors: Division of Clinical Biochemistry and Immunology, Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, Minnesota.
authors: Alicia
authors: A
authors: Algeciras-Schimnich
authors: Division of Clinical Biochemistry and Immunology, Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, Minnesota.
authors: Stefan K
authors: SK
authors: Grebe
authors: Division of Clinical Biochemistry and Immunology, Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, Minnesota.
authors: Leslie J
authors: LJ
authors: Donato
authors: Division of Endocrinology, Metabolism and Nutrition, Department of Medicine, Mayo Clinic, Rochester, Minnesota.
authors: Todd B
authors: TB
authors: Nippoldt
authors: Division of Endocrinology, Metabolism and Nutrition, Department of Medicine, Mayo Clinic, Rochester, Minnesota.
authors: Dana
authors: D
authors: Erickson
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D005951:Glucose Tolerance Test; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000032:analysis*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged
chemical_list: D007334:Insulin-Like Growth Factor I