title: [Comparative measurement of urine specific gravity: reagent strips, refractometry and hydrometry].
abstract: BACKGROUND
  The urine specific gravity is commonly used in clinical practice to measure the renal concentration/dilution ability. Measurement can be performed by three methods: hydrometry, refractometry and reagent strips.
  
  
  OBJECTIVE
  To assess the accuracy of different methods to measure urine specific gravity.
  
  
  METHODS
  We analyzed 156 consecutive urine samples of pediatric patients during April and May 2007. Urine specific gravity was measured by hydrometry (UD), refractometry (RE) and reagent strips (TR), simultaneously. Urine osmolarity was considered as the gold standard and was measured by freezing point depression. Correlation between different methods was calculated by simple linear regression.
  
  
  RESULTS
  A positive and acceptable correlation was found with osmolarity for the RE as for the UD (r= 0.81 and r= 0.86, respectively). The reagent strips presented low correlation (r= 0.46). Also, we found good correlation between measurements obtained by UD and RE (r= 0.89). Measurements obtained by TR, however, had bad correlation when compared to UD (r= 0.46). Higher values of specific gravity were observed when measured with RE with respect to UD.
  
  
  CONCLUSIONS
  Reagent strips are not reliable for measuring urine specific gravity and should not be used as an usual test. However, hydrometry and refractometry are acceptable alternatives for measuring urine specific gravity, as long as the same method is used for follow-up.
authors.affiliation: Unidad de Nefrología, Hospital de Niños Ricardo Gutiérrez. c.eliascosta@gmail.com
authors.forename: Christian Elías
authors.initials: CE
authors.lastname: Costa
authors.forename: Carolina
authors.initials: C
authors.lastname: Bettendorff
authors.forename: Sol
authors.initials: S
authors.lastname: Bupo
authors.forename: Sandra
authors.initials: S
authors.lastname: Ayuso
authors.forename: Graciela
authors.initials: G
authors.lastname: Vallejo
mesh_terms: D002648:Child; D003430:Cross-Sectional Studies; D006801:Humans; D011446:Prospective Studies; D011934:Reagent Strips; D012031:Refractometry; D013046:Specific Gravity; D016482:Urinalysis / Q000379:methods*; D014556:Urine
chemical_list: D011934:Reagent Strips