title: Interlaboratory agreement of insulin-like growth factor 1 concentrations measured by mass spectrometry.
abstract: BACKGROUND
  Insulin-like growth factor 1 (IGF-1)(7) is a key mediator of growth hormone (GH) action and a well-characterized biomarker of GH abuse. Current immunoassays for IGF-1 suffer from poor concordance between platforms, which makes comparison of results between laboratories difficult. Although previous work has demonstrated good interlaboratory imprecision of LC-MS/MS methods when plasma is supplemented with purified proteins, the interlaboratory imprecision of an endogenous protein in the nanogram-per-milliliter concentration range has not been reported.
  
  
  METHODS
  We deployed an LC-MS/MS method to quantify serum IGF-1 in 5 laboratories using 5 different instruments and analyzed 130 healthy human samples and 22 samples from patients with acromegaly. We determined measurement imprecision (CV) for differences due to instrumentation, calibration curve construction, method of calibration, and reference material.
  
  
  RESULTS
  Instrument-dependent variation, exclusive of digestion, across 5 different instrument platforms was determined to be 5.6%. Interlaboratory variation was strongly dependent on calibration. Calibration materials from a single laboratory resulted in less variation than materials made in individual laboratories (CV 5.2% vs 12.8%, respectively). The mean imprecision for 152 samples between the 5 laboratories was 16.0% when a calibration curve was made in each laboratory and 11.1% when a single-point calibration approach was used.
  
  
  CONCLUSIONS
  The interlaboratory imprecision of serum IGF-1 concentrations is acceptable for use of the assay in antidoping laboratories and in standardizing results across clinical laboratories. The primary source of variability is not derived from the sample preparation but from the method of calibration.
authors: Sports Medicine Research and Testing Laboratory, Salt Lake City, UT;
authors: Holly D
authors: HD
authors: Cox
authors: Filipe
authors: F
authors: Lopes
authors: Getachew A
authors: GA
authors: Woldemariam
authors: Jessica O
authors: JO
authors: Becker
authors: Mark C
authors: MC
authors: Parkin
authors: Andreas
authors: A
authors: Thomas
authors: Anthony W
authors: AW
authors: Butch
authors: David A
authors: DA
authors: Cowan
authors: Mario
authors: M
authors: Thevis
authors: Larry D
authors: LD
authors: Bowers
authors: Andrew N
authors: AN
authors: Hoofnagle
mesh_terms: D000172:Acromegaly / Q000097:blood; D002138:Calibration; D016022:Case-Control Studies; D002853:Chromatography, Liquid / Q000592:standards; D006801:Humans; D007118:Immunoassay / Q000592:standards; D007334:Insulin-Like Growth Factor I / Q000032:analysis* / Q000592:standards; D053719:Tandem Mass Spectrometry / Q000295:instrumentation / Q000592:standards
chemical_list: D007334:Insulin-Like Growth Factor I