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.

Chronic kidney disease (CKD) is a worldwide public health problem, with increasing prevalence, poor outcomes, and high treatment costs.¹ Yet despite the availability of simple laboratory tests to identify people with earlier stages of CKD, there are fewer clinical trials for kidney disease than for other common diseases.² One contributing reason may be that the established end point (ie, a doubling of serum creatinine concentration from baseline, corresponding to a 57% reduction in estimated glomerular filtration rate [GFR]) used to document CKD progression is a late event, requiring long follow-up periods and large sample sizes.^2-4 Improved methods for GFR estimation may allow for use of smaller reductions in estimated GFR (vs a doubling of serum creatinine concentration) as alternative end points to assess CKD progression.^4,5 Evaluation of such alternative end points should include their enumeration and quantification of their relationship with future progression to end-stage renal disease (ESRD) across a wide range of settings. Standardized definitions of CKD progression outcomes would also benefit observational studies and clinical practice.