Urine sodium concentration and diuretic responsiveness in dogs receiving orally administered loop diuretics for chronic congestive heart failure.

Urine sodium concentration identifies poor diuretic responsiveness in dogs with chronic CHF regardless of diuretic dose.

This prospective longitudinal observational study investigated urine sodium concentration (uNa) as a marker of diuretic responsiveness (DR) in 11 client-owned dogs receiving oral loop diuretics for chronic congestive heart failure (CHF). Owners collected 189 convenience urine samples over 5 days, which were analyzed for electrolyte, creatinine, and loop diuretic concentrations. The median uNa was 27 mmol/L (IQR 10–61 mmol/L), reflecting considerable individual variability. Notably, 5 of 11 dogs (45%) consistently demonstrated uNa below 70 mmol/L, a threshold indicative of low diuretic responsiveness. Neither diuretic dose, duration of oral diuretic treatment, time since last diuretic administration, nor time since last feeding were significantly associated with uNa. Urine diuretic concentration also failed to reach statistical significance in predicting uNa (β = 0.29; 95% CI, −0.03 to 0.61; P = .08). Despite small sample size, observed patterns of uNa alongside diuretic dose and urine diuretic concentration suggested mechanistic hypotheses for low DR, including inadequate diuretic absorption, diuretic resistance, or pathophysiologic adaptations. The authors conclude that uNa measurement in conjunction with urine diuretic concentration can identify dogs with suboptimal natriuresis that cannot be predicted by dose or treatment duration alone. These findings parallel human chronic CHF literature linking low uNa to adverse outcomes and support further investigation of uNa-guided diuretic management in canine cardiology, pending validation in larger cohorts.

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