title: The preservation of urine samples for determination of renal stone risk factors.
abstract: A preservation technique for urine specimens before determination of stone risk factors was evaluated.  The purpose of these experiments was to prove the effectiveness of the preservatives used to prevent changes in the concentrations of those constituents measured.  Measured concentrations in fresh specimens were compared with those in the same specimens after storage with the preservatives.  Refrigeration at 4 degrees C up to five days was appropriate in a laboratory setting, as no significant changes in urinary concentrations occurred.  Refrigeration, however, did not offer a convenient method for shipping.  Chemical preservation was found to be an effective alternative to refrigeration.  Thymol prevented changes in concentration of pH, citrate, uric acid, sulfate, sodium, potassium, and cyclic AMP, while a mixture of hydrochloric (HCl) acid and boric acid prevented changes in calcium, magnesium, phosphorus, oxalate, ammonium, and creatinine.  Thus, the addition of thymol or HCl/boric acid to urine specimens will prevent significant changes in the concentrations of stone risk factors.
authors.affiliation: Center on Mineral Metabolism and Clinical Research, Southwestern Medical School of the University of Texas Health Science Center at Dallas, TX 75235, USA.
authors.forename: M J
authors.initials: MJ
authors.lastname: Nicar
authors.forename: M C
authors.initials: MC
authors.lastname: Hsu
authors.forename: T
authors.initials: T
authors.lastname: Johnson
authors.forename: C Y
authors.initials: CY
authors.lastname: Pak
mesh_terms: D001888:Boric Acids / Q000494:pharmacology; D006801:Humans; D006851:Hydrochloric Acid / Q000494:pharmacology; D007669:Kidney Calculi / Q000175:diagnosis*; D011309:Preservation, Biological / Q000379:methods*; D011310:Preservatives, Pharmaceutical / Q000494:pharmacology*; D012034:Refrigeration; D012307:Risk Factors; D013048:Specimen Handling / Q000379:methods*; D013943:Thymol / Q000494:pharmacology; D016482:Urinalysis
chemical_list: D001888:Boric Acids; D011310:Preservatives, Pharmaceutical; D013943:Thymol; D006851:Hydrochloric Acid; C032688:boric acid