title: Hyponatremia with Persistent Elevated Urinary Fractional Uric Acid Excretion: Evidence for Proximal Tubular Injury?
abstract: OBJECTIVE
  Hyponatremia associated with high urinary fractional excretion of uric acid which persists after serum sodium is corrected is the cardinal feature of salt losing nephropathy (SLN). We hypothesize that low grade proximal tubular injury is present in SLN because the proximal tubule is the main site of uric acid and sodium transport.
  
  
  METHODS
  Five subjects with SLN were compared to four subjects with recurrent hyponatremia and three healthy individuals. Urinary NGAL (neutrophil gelatinase associated lipocalin, a marker of tubular injury) and fasting urinary fructose levels (a marker of proximal tubular injury) were measured.
  
  
  RESULTS
  Subjects with SLN (n=5) showed elevated fractional uric acid excretion (22 ± 6 vs 4 ± 2 percent, p<0.0001), elevated urinary NGAL levels (62 ± 37 vs 9 ± 7 ng/mg creatinine, p=0.001) and fasting urinary fructose levels compared with the 7 controls (383 ± 465 vs 60 ± 34µmole/µg creatinine, p <0.001). A strong correlation between urinary NGAL levels and urinary fructose levels was observed (r =0.87, p‹0.001).
  
  
  CONCLUSIONS
  High urinary fractional excretion of uric acid in SLN is associated with elevated NGAL and fasting urinary fructose levels suggesting that SLN may involve tubular injury.
authors: Biotronics Kidney Centers, Beaumont, Texas, Mexico.
authors: S-M Kurt
authors: SK
authors: Lee
authors: Miguel A
authors: MA
authors: Lanaspa
authors: Laura G
authors: LG
authors: Sánchez-Lozada
authors: Richard J
authors: RJ
authors: Johnson
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D005632:Fructose / Q000652:urine; D006801:Humans; D007010:Hyponatremia / Q000652:urine*; D007674:Kidney Diseases; D007687:Kidney Tubules, Proximal / Q000293:injuries*; D000071068:Lipocalin-2 / Q000652:urine; D008297:Male; D008875:Middle Aged; D012964:Sodium / Q000097:blood; D014527:Uric Acid / Q000652:urine*; D055815:Young Adult
chemical_list: D000071068:Lipocalin-2; D014527:Uric Acid; D005632:Fructose; D012964:Sodium