title: Biochemical profile of idiopathic uric acid nephrolithiasis.
abstract: BACKGROUND
  The objective of this study was to elucidate a biochemical profile of patients with idiopathic uric acid nephrolithiasis, without secondary causes (such as dehydration or diarrhea). Study subjects comprised 56 patients with idiopathic uric acid nephrolithiasis (UA stone group) who underwent a full outpatient evaluation. The control group was composed of 54 with absorptive hypercalciuria and 2 normal subjects, matched with the UA stone group according to age, body mass index, and gender.
  
  
  METHODS
  Urinary pH and ammonium and serum and urinary uric acid were measured. The fractional excretion of urate was calculated.
  
  
  RESULTS
  Compared with the control group, the UA stone group had a significantly higher serum uric acid and significantly lower urinary uric acid, pH (5.34 +/- 0.23 vs. 6.17 +/- 0.36, P < 0.001), and fractional excretion of urate (0.052 +/- 0.028 vs. 0.080 +/- 0.029, P < 0.001), but individual values overlapped considerably between the two groups. Discriminant analysis of the relationship between urinary pH and fractional excretion of urate yielded a "discriminant score," which provided a much better separation between the two groups, with a correct classification in 95.5% of subjects. In contrast, urinary ammonium, citrate, sulfate, and potassium did not differ between two groups.
  
  
  CONCLUSIONS
  In idiopathic uric acid nephrolithiasis, urinary pH and fractional excretion of urate are significantly lower than in control subjects, suggestive of defects in urinary acidification and urate excretion. Since these impairments are believed to be associated with primary gout, the underlying disturbance in idiopathic uric acid nephrolithiasis may be primary gout.
authors.affiliation: Center for Mineral Metabolism and Clinical Research, University of Texas Southwestern Medical Center, Dallas, Texas 75390-8885, USA. charles.pak@utsouthwestern.edu
authors.forename: C Y
authors.initials: CY
authors.lastname: Pak
authors.forename: K
authors.initials: K
authors.lastname: Sakhaee
authors.forename: R D
authors.initials: RD
authors.lastname: Peterson
authors.forename: J R
authors.initials: JR
authors.lastname: Poindexter
authors.forename: W H
authors.initials: WH
authors.lastname: Frawley
mesh_terms: D000328:Adult; D005260:Female; D006073:Gout / Q000097:blood / Q000652:urine; D006801:Humans; D006863:Hydrogen-Ion Concentration; D015228:Hypertriglyceridemia / Q000097:blood / Q000652:urine; D007669:Kidney Calculi / Q000097:blood / Q000737:chemistry* / Q000652:urine*; D008297:Male; D008875:Middle Aged; D000644:Quaternary Ammonium Compounds / Q000652:urine; D014527:Uric Acid / Q000097:blood / Q000652:urine*
chemical_list: D000644:Quaternary Ammonium Compounds; D014527:Uric Acid