Spot Urinary Electrolytes and Creatinine for Guiding Loop Diuretic Therapy in Acute Heart Failure: Pathophysiologic Rationale, Evidence, and Practical Implementation.

Congestion is the dominant driver of hospitalization in acute heart failure and relief of congestion remains a central therapeutic target. Loop diuretics are first-line therapy for decongestion, yet their dosing and escalation in routine practice often rely on subjective bedside assessment, variable urine output thresholds, weight change, and delayed laboratory trends approaches that incompletely capture the primary pharmacodynamic goal of diuretic therapy: natriuresis. Neurohormonal activation and renal sodium avidity in heart failure can lead to poor diuretic response despite apparently adequate diuretic dosing, and persistent congestion is consistently associated with adverse outcomes. In this context, early measurement of spot urinary electrolytes especially urinary sodium, and potentially urinary chloride and urinary creatinine offers an objective, rapid method to quantify natriuretic response and identify inadequate decongestion early enough to adjust therapy. This review summarizes the pathophysiologic basis linking renal sodium handling to congestion, critiques traditional metrics used to titrate diuretics, synthesizes the clinical evidence supporting spot urinary sodium-based assessment (observational cohorts and emerging randomized/protocolized strategies), and outlines pragmatic implementation considerations, including confounders such as chronic kidney disease, concomitant SGLT2 inhibitors, and timing of sampling. While natriuresis-guided strategies reliably improve natriuresis and process-of-care metrics, definitive evidence for improved hard outcomes remains evolving, underscoring the need for standardized protocols and larger outcomes trials.