SAT-269 URINE ESTIMATED AMMONIUM-TO-CREATININE RATIO IN PATIENTS WITH CHRONIC KIDNEY DISEASE.

Abstract

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. We measured u-eNH4+/u-Cr in outpatients without overt metabolic acidosis (5.0< [urinary pH] <7.0, [HCO3-] >20 mEq/L, no medication of bicarbonate). The estimated ammonium concentration (u-eNH4+) from the osmolar gap was calculated as u-eNH4+=0.5x(osmolality-2[Na++K+]-[urea]/2.8-[glucose]/18). A total of 168 outpatients were identified (Mean age; 63.1 ± 18.0 years old, Male; 59.5%, CKD; 54.8%, Hypertensives; 74.4%, Diabetes; 35.1%). Although u-eNH4+/u-Cr showed a positive correlation with eGFR (P = 0.0151) (Fig.1), no associations were observed between eNH4+/u-Cr with age, BMI, uPCR, pH, HCO3-, BE, or Anion gap. Interestingly, eNH4+/u-Cr was significantly lower in CKD stage 3-5 than in non-CKD groups (Fig 2), even though there were no overt metabolic acidosis.Fig. 2View Large Image Figure ViewerDownload Hi-res image Download (PPT) u-eNH4+/u-Cr is easily measured in clinical practice and would be more tightly linked with ammonium excretion than serum bicarbonate and other acid-base indicators.