Abstract
Hyponatremia is the most common electrolyte abnormality. Its diagnostic and therapeutic approaches are in a state of flux. It is evident that hyponatremic patients are symptomatic with a potential for serious consequences at sodium levels that were once considered trivial. The recommendation to treat virtually all hyponatremics exposes the need to resolve the diagnostic and therapeutic dilemma of deciding whether to water restrict a patient with the syndrome of inappropriate antidiuretic hormone secretion (SIADH) or administer salt and water to a renal salt waster. In this review, we briefly discuss the pathophysiology of SIADH and renal salt wasting (RSW), and the difficulty in differentiating SIADH from RSW, and review the origin of the perceived rarity of RSW, as well as the value of determining fractional excretion of urate (FEurate) in differentiating both syndromes, the high prevalence of RSW which highlights the inadequacy of the volume approach to hyponatremia, the importance of changing cerebral salt wasting to RSW, and the proposal to eliminate reset osmostat as a subtype of SIADH, and finally propose a new algorithm to replace the outmoded volume approach by highlighting FEurate. This algorithm eliminates the need to assess the volume status with less reliance on determining urine sodium concentration, plasma renin, aldosterone and atrial/brain natriuretic peptide or the BUN to creatinine ratio.
Highlights
Hyponatremia, defined as serum sodium
It is extremely difficult to differentiate SIADH from renal salt wasting (RSW) largely because of significant overlapping of clinical and laboratory findings and the perception that RSW is a rare clinical entity. This differentiation is extremely important because of divergent therapeutic goals of appropriately water restricting those with SIADH and increasing salt and water with RSW to avoid iatrogenic increases in morbidity and mortality
The volume approach to hyponatremia and perception that RSW is a rare clinical entity should be abandoned in favor of a more open-minded approach that will lead to better diagnosis and treatment of hyponatremic conditions
Summary
Hyponatremia, defined as serum sodium
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