The recent research findings concerning syndromes of muscle wasting, malnutrition, and inflammation in individuals with chronic kidney disease (CKD) or acute kidney injury (AKI) have led to a need for new terminology. To address this need, the International Society of Renal Nutrition and Metabolism (ISRNM) convened an expert panel to review and develop standard terminologies and definitions related to wasting, cachexia, malnutrition, and inflammation in CKD and AKI. The ISRNM expert panel recommends the term ‘protein–energy wasting’ for loss of body protein mass and fuel reserves. ‘Kidney disease wasting’ refers to the occurrence of protein–energy wasting in CKD or AKI regardless of the cause. Cachexia is a severe form of protein–energy wasting that occurs infrequently in kidney disease. Protein–energy wasting is diagnosed if three characteristics are present (low serum levels of albumin, transthyretin, or cholesterol), reduced body mass (low or reduced body or fat mass or weight loss with reduced intake of protein and energy), and reduced muscle mass (muscle wasting or sarcopenia, reduced mid-arm muscle circumference). The kidney disease wasting is divided into two main categories of CKD- and AKI-associated protein–energy wasting. Measures of chronic inflammation or other developing tests can be useful clues for the existence of protein–energy wasting but do not define protein–energy wasting. Clinical staging and potential treatment strategies for protein–energy wasting are to be developed in the future.

The broad clinical syndrome of acute kidney injury (AKI) encompasses various aetiologies, including specific kidney diseases (e.g. acute interstitial nephritis), non-specific conditions (e.g. renal ischaemia) as well as extrarenal pathology (e.g. post-renal obstruction). AKI is a serious condition that affects kidney structure and function acutely, but also in the long term. Recent epidemiological evidence supports the notion that even mild, reversible AKI conveys the risk of persistent tissue damage, and severe AKI can be accompanied by an irreversible decline of kidney function and progression to end-stage kidney failure [ 1–3].