title: Glucose and insulin variations in patients during the time course of a FDG-PET study and implications for the "glucose-corrected" SUV.
abstract: BACKGROUND
  2-Deoxy-2[(18)F]fluoro-d-glucose (FDG) positron emission tomography (PET) has an established role in the evaluation of cancer. Generally, tumor uptake and response to treatment are evaluated using the standardized uptake value (SUV). Some authors have proposed correcting SUV for glucose levels. Insulin is also thought to influence tumor uptake by changing uptake in other tissues. However, little attention has been paid to understanding the variability of glucose or insulin during a single PET study.
  
  
  METHODS
  We studied the biological and instrumental variability of glucose and insulin measurements in 71 nondiabetic patients undergoing FDG-PET studies. Multiple glucose measurements were obtained in all 71 subjects, and in 69 of these 71 subjects, multiple serum insulin measurements were made. We determined the coefficient of observed variation (CV(ow)) and the coefficient of variation attributable to biological variability (CV(bv)) for both glucose and insulin.
  
  
  RESULTS
  The mean glucose concentration was 78.9+/-13.5 mg/dl. The mean insulin value was 6.49+/-5.92 microU/ml. The weighted mean CV(ow) and CV(bv) was 5.0% and 3.6%, respectively, for glucose and 14.2% and 8.3%, respectively, for insulin.
  
  
  CONCLUSIONS
  Variations in the range of 3.6% are observed in glucose measurements during the time course of an FDG scan even after accounting for analytical error; larger variations of 8.3% are observed in insulin levels. Therefore, corrections of SUV for blood glucose, especially if obtained from single measurements, can introduce additional errors of at least this much.
authors.affiliation: Department of Radiology, University of California, San Francisco, CA 94158, USA. dochadi@gmail.com
authors.forename: Mohiuddin
authors.initials: M
authors.lastname: Hadi
authors.forename: Stephen L
authors.initials: SL
authors.lastname: Bacharach
authors.forename: Millie
authors.initials: M
authors.lastname: Whatley
authors.forename: Steven K
authors.initials: SK
authors.lastname: Libutti
authors.forename: Stephen E
authors.initials: SE
authors.lastname: Straus
authors.forename: V Koneti
authors.initials: VK
authors.lastname: Rao
authors.forename: Robert
authors.initials: R
authors.lastname: Wesley
authors.forename: Jorge A
authors.initials: JA
authors.lastname: Carrasquillo
mesh_terms: D001692:Biological Transport; D001786:Blood Glucose / Q000032:analysis* / Q000378:metabolism; D019788:Fluorodeoxyglucose F18 / Q000493:pharmacokinetics; D005947:Glucose / Q000031:analogs & derivatives / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000097:blood*; D009369:Neoplasms / Q000000981:diagnostic imaging; D015588:Observer Variation; D049268:Positron-Emission Tomography / Q000379:methods*; D012015:Reference Standards; D014018:Tissue Distribution
chemical_list: D001786:Blood Glucose; D007328:Insulin; D019788:Fluorodeoxyglucose F18; D005947:Glucose