Appropriate interpretation of changes in markers of kidney function is essential during the treatment of acute and chronic heart failure. Historically, kidney function was primarily assessed by serum creatinine and the calculation of estimated glomerular filtration rate. An increase in serum creatinine, also termed worsening renal function, commonly occurs in patients with heart failure, especially during acute heart failure episodes. Even though worsening renal function is associated with worse outcome on a population level, the interpretation of such changes within the appropriate clinical context helps to correctly assess risk and determine further treatment strategies. Additionally, it is becoming increasingly recognized that assessment of kidney function is more than just glomerular filtration rate alone. As such, a better evaluation of sodium and water handling by the renal tubules allows to determine the efficiency of loop diuretics (loop diuretic response and efficiency). Also, though neurohumoral blockers may induce modest deteriorations in glomerular filtration rate, their use is associated with improved long‐term outcome. Therefore, a better understanding of the role of cardio–renal interactions in heart failure in symptom development, disease progression and prognosis is essential. Indeed, perhaps even misinterpretation of kidney function is a leading cause of not attaining decongestion in acute heart failure and insufficient dosing of guideline‐directed medical therapy in general. This position paper of the Heart Failure Association Working Group on Cardio‐Renal Dysfunction aims at improving insights into the interpretation of renal function assessment in the different heart failure states, with the goal of improving heart failure care.

Current pathophysiological models of congestive heart failure unsatisfactorily explain the detrimental link between congestion and cardiorenal function. Abdominal congestion (i.e., splanchnic venous and interstitial congestion) manifests in a substantial number of patients with advanced congestive heart failure, yet is poorly defined. Compromised capacitance function of the splanchnic vasculature and deficient abdominal lymph flow resulting in interstitial edema might both be implied in the occurrence of increased cardiac filling pressures and renal dysfunction. Indeed, increased intra-abdominal pressure, as an extreme marker of abdominal congestion, is correlated with renal dysfunction in advanced congestive heart failure. Intriguing findings provide preliminary evidence that alterations in the liver and spleen contribute to systemic congestion in heart failure. Finally, gut-derived hormones might influence sodium homeostasis, whereas entrance of bowel toxins into the circulatory system, as a result of impaired intestinal barrier function secondary to congestion, might further depress cardiac as well as renal function. Those toxins are mainly produced by micro-organisms in the gut lumen, with presumably important alterations in advanced heart failure, especially when renal function is depressed. Therefore, in this state-of-the-art review, we explore the crosstalk between the abdomen, heart, and kidneys in congestive heart failure. This might offer new diagnostic opportunities as well as treatment strategies to achieve decongestion in heart failure, especially when abdominal congestion is present. Among those currently under investigation are paracentesis, ultrafiltration, peritoneal dialysis, oral sodium binders, vasodilator therapy, renal sympathetic denervation and agents targeting the gut microbiota.

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