Table 4.

Associations between urine ammonium and each urine anion gap measurement with the composite outcome of dialysis or death before dialysis

Composite Outcome (Death or ESRD)Urine AmmoniumUAGUAGSO4UAGPO4UAGPLUS
Tertile corresponding with
Low urine ammonium or high UAG
 Hazard ratio (95% CI)1.46 (1.13 to 1.87)0.82 (0.64 to 1.07)0.94 (0.72 to 1.21)0.95 (0.74 to 1.21)1.32 (1.03 to 1.68)
 Mean (SD) urine ammonium, mEq/d10.2 (3.3)23.9 (12.9)18.8 (10.4)20.4 (12.4)14.9 (9.0)
 No. of events18815163153174
Intermediate urine ammonium or UAG
 Hazard ratio (95% CI)1.14 (0.89 to 1.46)0.82 (0.65 to 1.03)0.93 (0.73 to 1.18)0.82 (0.65 to 1.04)1.23 (0.97 to 1.56)
 Mean (SD) urine ammonium, mEq/d19.5 (2.6)21.6 (10.9)19.6 (10.3)21.3 (11.4)18.8 (8.3)
 No. of events146150163156159
High urine ammonium or low UAG
 Hazard ratio (95% CI)ReferenceReferenceReferenceReferenceReference
 Mean (SD) urine ammonium, mEq/d34.6 (9.3)18.7 (10.5)25.8 (12.8)22.5 (12.4)30.4 (11.3)
 No. of events130163138155131
  • Models were adjusted for age, sex, randomized group, measured GFR, proteinuria, net endogenous acid production, serum potassium, and serum bicarbonate and stratified by body mass index. Also shown are the mean (SD) values of urine ammonium within each tertile of UAG and the numbers of events within each tertile (number at risk =348 in each). The concentrations of urine ammonium are in the opposite direction expected in the UAG group. Inclusion of sulfate (UAGSO4) and phosphate (UAGPO4) yielded the expected pattern of higher urine ammonium concentration with lower (more negative) UAG. UAGPLUS showed the best separation of urine ammonium in the expected direction across the tertiles. Only UAGPLUS recapitulated the hazard ratios of the composite outcome observed with urine ammonium. UAG, urine anion gap; UAGSO4, urine anion gap with inclusion of urine sulfate; UAGPO4, urine anion gap with inclusion of urine phosphate; UAGPLUS, urine anion gap with inclusion of urine phosphate and sulfate; 95% CI, 95% confidence interval.