Background Impaired renal ammonia production plays a significant role in the pathogenesis of metabolic acidosis in patients with chronic kidney disease (CKD), and may have prognostic value. Measurement of urinary ammonia, reported as urine ammonia-to-creatinine ratio (UACR) is the gold standard for evaluation. The biological variability of UACR and its impact on diagnostic utility is unknown in healthy dogs and those with CKD.
Hypothesis/Objectives The primary aim of this study was to determine intra-individual and between-subjectbiological variation of UACR within-day and week-to-week in healthy adult dogs.
Animals Twenty-eight adult, client-owned dogs considered healthy based on history, physical examination, serum chemistry, and urinalysis.
Methods Prospective observational cohort study. Daily collection of urine samples from each dog at 0, 4, and 8 hours, repeated once weekly for six weeks. Urinary ammonia and creatinine concentrations were measured using commercially available enzymatic assays and used to calculate UACR. Ammonia, creatinine and UACR were analyzed using linear hierarchical mixed-models. Repeatability was quantified by calculating intraclass correlation coefficient.
Results Average week to week values were relatively stable (ammonia p = 0.33, creatinine p = 0.85, UACR p = 0.42). Within-day repeatability was poor because of strong effects of time of day on creatinine. Conclusions and Clinical Importance Within-individual UACR in healthy dogs showed minimal variation week-to-week. Time of day in which samples are collected impacts UACR individual repeatability and should be standardized between measurements.
