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Abstract: TH-OR074

The Potential Utility of Urine Estimated Ammonium-to-Creatinine Ratio in Patients with CKD

Session Information

Category: Fluid and Electrolytes

  • 902 Fluid and Electrolytes: Clinical

Authors

  • Hatanaka, Saeko, The Jikei University School of Medicine, Tokyo, Japan
  • Kanzaki, Go, The Jikei University School of Medicine, Tokyo, Japan
  • Hatano, Satoki, Atsugi City Hospital, Kanagawa, Japan
  • Matsumoto, Naoto, The Jikei University School of Medicine, Tokyo, Japan
  • Nakada, Yasuyuki, Atsugi City Hospital, Kanagawa, Japan
  • Maruyama, Yukio, The Jikei University School of Medicine, Tokyo, Japan
  • Tsuboi, Nobuo, The Jikei University School of Medicine, Tokyo, Japan
  • Yokoo, Takashi, The Jikei University School of Medicine, Tokyo, Japan
Background

Renal ammonium (NH4+) excretion plays a critical role in the elimination of acid. Recent studies have reported that the impairment in urinary NH4+ excretion is an important determinant of the development of metabolic acidosis and is an independent factor for predicting loss of renal function. However, urine ammonium measurements are not widely available in routine diagnostic laboratories, and its clinical significance is still unknown. We hypothesized that urine estimated ammonium-to-creatinine ratio (u-eNH4+/u-Cr), as an indicator of urinary NH4+ excretion, would be surrogates for early metabolic acidosis in patients with CKD.

Methods

We measured u-eNH4+/u-Cr in outpatients without receiving oral alkali, hypokalemia, urinary acid-base imbalance, and negative value of urine anion gap (UAG) and urinary osmolar gap (UOG). The urine estimated ammonium concentration (u-eNH4+) from UOG was calculated as u-eNH4+ = 0.5 x (urine osmolality - 2[Na+ + K+] - [urea] - [glucose]). In a multiple regression model, the factors that had affected u-eNH4+/u-Cr ware examined. Receiver operating characteristic (ROC)-plot area under the curve (AUC) was used to show the effectiveness of u-eNH4+/u-Cr.

Results

A total of 464 outpatients were identified (Mean age, 66.4 ± 15.8 years old; Male, 57.7%; CKD, 58.8%; Hypertensives, 70.9%; Diabetes, 40.0%). u-eNH4+/u-Cr was associated positively with sex, eGFR, potassium, uric acid, blood glucose, UAG, and urine protein creatinine ratio. Interestingly, u-eNH4+/u-Cr was significantly lower in CKD stage 4-5 than in non-CKD groups, even though there were no overt metabolic disorders. Sex, eGFR, serum potassium level, and blood glucose were independently associated with u-eNH4+/u-Cr in a multiple regression model. In addition, AUC values for u-eNH4+/u-Cr had greater identity with the metabolic acidosis than ROC-plot AUC values for serum or urinary anion gap (mean ROC-plot AUC for u-eNH4+/u-Cr, 0.638; 95% CI, 0.550 to 0.726; p=0.007).

Conclusion

u-eNH4+/u-Cr is easily measured in clinical practice and would be more tightly linked with ammonium excretion than serum or urinary anion gap.