The dynamic relationship between serum chloride and cardiorenal syndrome.

Low serum sodium concentration has long been recognized as an established marker of short- and long-term morbidity and mortality in patients with heart failure (HF), and is commonly included in various risk prediction models. Mechanisms leading to hyponatremia (e.g. maladaptive neurohormonal activation) could also lead to concurrent decline in serum chloride levels. Besides, chloride has distinct biological roles (e.g. modulation of renal tubular sodium transporters) that are relevant to the pathophysiology and therapy of HF, making it a potent cardiorenal connector. Several clinical studies have recently reported on a potentially overlooked link between low serum chloride levels and adverse outcomes in patients with a wide variety of HF syndromes, which could indeed be stronger than that of sodium. While evidence on predictive value of chloride is accumulating in various patient populations and settings, the limited available interventional studies have so far yielded conflicting results. It remains to be elucidated whether hypochloremia represents a marker of disease severity and prognosis, or it is an actual pathogenetic mechanism, hence being a potential novel target of therapy. Current ongoing studies are designed to better understand the mechanistic aspects of the role of hypochloremia in HF and shed light on its clinical applicability.