Spot urinary electrolytes are associated with decongestion and duration of hospitalization in dogs with acute left-sided congestive heart failure secondary to myxomatous mitral valve disease.

OBJECTIVE

To determine whether urinary electrolyte indices measured after IV furosemide administration are associated with clinical outcomes in dogs with left-sided acute congestive heart failure (CHF) secondary to myxomatous mitral valve disease (MMVD).

METHODS

In this multicenter retrospective study, client-owned dogs with acute left-sided CHF caused by MMVD presenting to 3 referral hospitals between January 2024 and December 2025 were evaluated. All dogs received a single IV bolus of furosemide (2 mg/kg) at presentation. Urine samples were collected from the first spontaneous urination within 2 hours after furosemide administration. Urinary sodium concentration, urinary sodium-to-potassium ratio (uNa:K), and urinary sodium-to-chloride ratio were measured. Associations between urinary electrolyte indices and clinical variables were analyzed. Clinical outcomes included change in radiographic pulmonary congestion score, hospitalization duration, and survival to discharge.

RESULTS

50 dogs met the inclusion criteria. Higher urinary sodium concentration and uNa:K were associated with greater improvement in radiographic pulmonary congestion and shorter hospitalization. Dogs that survived to discharge had a higher uNa:K than those that died during hospitalization. Urinary electrolyte indices were not significantly correlated with echocardiographic or radiographic indices of left atrial size.

CONCLUSIONS

Urinary electrolyte indices measured after IV furosemide administration were associated with clinically relevant outcomes in dogs hospitalized with acute left-sided CHF secondary to MMVD.

CLINICAL RELEVANCE: Spot urinary electrolyte measurements may provide a simple and noninvasive tool for assessing diuretic response and clinical status in dogs with acute left-sided CHF.