title: Comparison of specific gravity and creatinine for normalizing urinary reproductive hormone concentrations.
abstract: BACKGROUND
  Specific gravity (SG) may perform as well as creatinine (CR) correction for adjusting urinary hormone concentrations, as well as offer some advantages. We compared the two methods and applied them to US and Bangladeshi specimens to evaluate their use in different populations.
  
  
  METHODS
  Pearson correlations between serum concentrations and SG, CR, and uncorrected urinary concentrations were compared using paired daily urine and serum specimens from one menstrual cycle from 30 US women. Corrected urinary estrone conjugate and pregnanediol glucuronide concentrations were compared with serum estradiol and progesterone. Urine specimens across one menstrual cycle from 13 Bangladeshi women were used to evaluate the applicability of both methods to a nonindustrialized population. Linear mixed-effects models were used to compare CR and SG values in the Bangladeshi vs US specimens.
  
  
  RESULTS
  There was no significant difference between SG-corrected vs serum and CR-corrected vs serum correlations for either assay. Usable CR results were obtained for all US specimens, but 37% of the Bangladeshi specimens were below the CR assay limit of detection. The Bangladeshi sample had significantly lower CR and higher inter- and intrasubject CR variability than the US sample.
  
  
  CONCLUSIONS
  SG is a potentially useful alternative to CR correction for normalizing urinary steroid hormone concentrations, particularly in settings where CR values are highly variable or unusually low.
authors.affiliation: Department of Anthropology and Center for Studies in Demography and Ecology, University of Washington, Seattle 98195, USA.
authors.forename: Rebecca C
authors.initials: RC
authors.lastname: Miller
authors.forename: Eleanor
authors.initials: E
authors.lastname: Brindle
authors.forename: Darryl J
authors.initials: DJ
authors.lastname: Holman
authors.forename: Jane
authors.initials: J
authors.lastname: Shofer
authors.forename: Nancy A
authors.initials: NA
authors.lastname: Klein
authors.forename: Michael R
authors.initials: MR
authors.lastname: Soules
authors.forename: Kathleen A
authors.initials: KA
authors.lastname: O'Connor
mesh_terms: D000328:Adult; D001459:Bangladesh; D003404:Creatinine / Q000652:urine*; D005260:Female; D012739:Gonadal Steroid Hormones / Q000097:blood / Q000652:urine*; D006801:Humans; D007124:Immunoenzyme Techniques; D008875:Middle Aged; D013046:Specific Gravity; D014481:United States; D016482:Urinalysis / Q000379:methods*
chemical_list: D012739:Gonadal Steroid Hormones; D003404:Creatinine