Nomenclature for kidney function and disease: Executive summary and glossary from a Kidney Disease: Improving Global Outcomes (KDIGO) consensus conference

Abstract

A primary obligation of medical journals is the responsible, professional, and expeditious delivery of knowledge from researchers and practitioners to the wider community [[1]Levey A.S. Weiner D.E. editorial team. Staying put, but not standing still.Am J Kidney Dis. 2012; 59: 1-3Abstract Full Text Full Text PDF PubMed Scopus (21) Google Scholar]. The task of journal editors, therefore, rests not merely in selecting what to publish, but in large measure judging how it can best be communicated. The challenge of improving descriptions of kidney function and disease in medical publishing was the impetus for a Kidney Disease: Improving Global Outcomes (KDIGO) Consensus Conference held in June 2019. The conference goals included standardizing and refining kidney-related nomenclature used in English-language scientific articles and developing a glossary that can be used by journals [[2]Kidney Disease: International Global Outcomes. Consensus conference on nomenclature for kidney function & disease. Available at: https://kdigo.org/conferences/nomenclature/ [accessed April 24, 2020].Google Scholar]. The rationale for the conference was that the worldwide burden of kidney disease is rising, but public awareness remains limited, underscoring the need for effective communication by stakeholders in the kidney health community [3Plantinga L.C. Boulware L.E. Coresh J. et al.Patient awareness of chronic kidney disease: trends and predictors.Arch Intern Med. 2008; 168: 2268-2275Crossref PubMed Scopus (210) Google Scholar, 4James S.L. Global, regional, and national incidence, prevalence, and years lived with disability for 354 diseases and injuries for 195 countries and territories, 1990–2017: a systematic analysis for the Global Burden of Disease Study 2017.Lancet. 2018; 392: 1789-1858Abstract Full Text Full Text PDF PubMed Scopus (3675) Google Scholar, 5GBD Chronic Kidney Disease Collaboration Global, regional, and national burden of chronic kidney disease, 1990–2017: a systematic analysis for the Global Burden of Disease Study 2017.Lancet. 2020; 395: 709-733Abstract Full Text Full Text PDF PubMed Scopus (770) Google Scholar, 6Saran R. Robinson B. Abbott K.C. et al.US Renal Data System 2017 annual data report: epidemiology of kidney disease in the United States.Am J Kidney Dis. 2018; 71: S1-S676PubMed Google Scholar]. Despite this need, the nomenclature for describing kidney function and disease lacks uniformity and clarity. Two decades ago, a survey of hundreds of published articles and meeting abstracts reported a broad array of overlapping, confusing terms for chronic kidney disease (CKD) and advocated adoption of unambiguous terminology [[7]Hsu C.Y. Chertow G.M. Chronic renal confusion: insufficiency, failure, dysfunction, or disease.Am J Kidney Dis. 2000; 36: 415-418Abstract Full Text Full Text PDF PubMed Scopus (105) Google Scholar]. Nevertheless, terms flagged by that analysis as problematic, such as “chronic renal failure” and “pre-dialysis,” still appear in current-day publications. A coherent, shared nomenclature could improve communication at all levels, to not only foster better appreciation of the burden of disease but also aid understanding of how patients feel about their disease, allow more effective communication between kidney disease specialists and other clinicians, advance more straightforward comparison and integration of datasets, enable better recognition of gaps in knowledge for future research, and facilitate more comprehensive public health policies for acute and chronic kidney disease. Developing consistent, patient-centered, and precise descriptions of kidney function and disease in the scientific literature is an important objective to align communication in clinical practice, research, and public health. Although some terms have been in use for decades, the increased exchange of information among stakeholders makes it timely to revisit nomenclature in order to ensure consistency. The goal is to facilitate communication within and across disciplines and between practitioners and patients, with the ultimate hope of improving outcomes through consistency and precision. Attendees at the conference included editors of kidney subspecialty journals, kidney subspecialty editors at general medical journals and journals from other subspecialties, experienced authors of clinical kidney health research, and patients. Guiding principles of the conference were that the revised nomenclature should be patient-centered, precise, and consistent with nomenclature used in the KDIGO guidelines. The discussion focused on general description of acute and chronic kidney disease and kidney measures, rather than specific kidney diseases and particular measures of function and structure. Classifications of causes of kidney disease and procedures, performance measures, and outcome metrics for dialysis and transplantation were considered beyond the scope of discussion. As described in detail in the conference report [[8]Levey AS, Eckardt K-U, Dorman NM, et al. Nomenclature for kidney function and disease: report of a Kidney Disease: Improving Global Outcomes (KDIGO) Consensus Conference. Kidney Int. 2020; 97: 1117-1129.Google Scholar], the meeting attendees reached general consensus on the following recommendations: (i) to use “kidney” rather than “renal” or “nephro-” when referring to kidney disease and kidney function; (ii) to use “kidney failure” with appropriate descriptions of presence or absence of symptoms, signs, and treatment rather than “end-stage kidney disease”; (iii) to use the KDIGO definition and classification of acute kidney diseases and disorders (AKD) and acute kidney injury (AKI) rather than alternative descriptions to define and classify the severity of these; (iv) to use the KDIGO definition and classification of CKD rather than alternative descriptions to define and classify it; and (v) to use specific kidney measures, such as albuminuria or decreased glomerular filtration rate, rather than “abnormal” or “reduced” kidney function to describe alterations in kidney structure and function (Table 1). Accordingly, the proposed glossary contains 5 corresponding sections, and comprises specific items for which there was general agreement among the conference participants (https://kdigo.org/conferences/nomenclature/; Table 2) [[8]Levey AS, Eckardt K-U, Dorman NM, et al. Nomenclature for kidney function and disease: report of a Kidney Disease: Improving Global Outcomes (KDIGO) Consensus Conference. Kidney Int. 2020; 97: 1117-1129.Google Scholar]. For each section, the glossary includes preferred terms, abbreviations, descriptions, and terms to avoid, with the acknowledgment that journals may choose which of the recommendations to implement, and that journal style will dictate when and how to abbreviate terms to be consistent with nomenclature for other diseases.Table 1Key takeaways from the conference.•Use the term “kidney” rather than “renal” to describe kidney function and kidney disease. In English, the terms renal and kidney are still used interchangeably, resulting in different acronyms describing the same condition or status (e.g., ESRD/ESKD and RRT/KRT). It is more likely that patients and the public would understand the terms incorporating the more familiar noun “kidney,” rather than the less familiar adjective “renal,” which is derived from Latin and is labeled as technical in some dictionaries. Although writing guides may generally favor using an appropriate adjective over a noun as a modifier, there are high-profile precedents for the use of kidney as a modifier, such as AKI, CKD, and NIDDK (National Institute of Diabetes and Digestive and Kidney Diseases).•Avoid the term “end-stage.” Although rooted in US law, the term is not patient sensitive, may connote a stigma, and may discourage advocacy. In the US, ESRD (ESKD) is a synonym for receipt of KRT. However, KRT is a treatment rather than a disease. The term “kidney failure,” which is defined as GFR < 15 ml/min per 1.73 m2 or treatment by dialysis, is as comprehensive as “ESRD/ESKD,” without suffering from its limitations.•Improve characterization of the full spectrum of kidney failure. Although all patients with kidney failure have GFR < 15 ml/min per 1.73 m2 or are undergoing treatment by dialysis, the severity of symptoms varies greatly. We lack terms to describe the severity of symptoms and signs, and yet they are indications for initiating KRT. There are also no common patient-reported outcome measures to describe severity. The term “kidney failure” in a chronic setting is defined as >3 months, whereas in an acute setting (i.e., AKI stage 3), it is reserved for a duration of ≤ 3 months. Kidney failure could be further classified according to patient-reported outcomes (symptoms).•Use more-descriptive terms for treatments for kidney failure. Many patients with kidney failure do not undergo KRT. The terms “treated” vs. “untreated” have been used, but this is not consistent with the idea that supportive care is indeed treatment. Furthermore, in some cases, patients choose supportive care rather than KRT; in other cases, they do not have a choice because of lack of insurance or lack of availability. Finally, some patients may not be under the care of a physician at all.•Avoid the use of “chronic kidney disease (CKD)” as a synonym for “GFR < 60 ml/min per 1.73 m2.” CKD includes markers of kidney damage or GFR < 60 ml/min per 1.73 m2 for >3 months, so ascertainment of GFR without assessment for markers of kidney damage is insufficient for classification of CKD status when GFR > 60 ml/min per 1.73 m2. If chronicity is not documented, it can be inferred on the basis of corroborative clinical data or presumed in the absence of clinical data to the contrary.•Avoid the use of “acute kidney injury (AKI)” as a synonym for “acute kidney diseases and disorders (AKD).” AKD refers to kidney diseases and disorders with a duration of ≤3 months, whereas AKI refers to kidney diseases and disorders with onset within 1 week.•Use “CKD GFR and albuminuria categories” and “AKI stages” to describe disease severity, rather than employing ill-defined terms such as “mild,” “moderate,” “severe,” and “advanced.”•Use the terms “GFR categories” and “albuminuria categories” rather than “CKD stages” when describing the level of GFR and albuminuria in populations either without CKD or without ascertainment of both GFR and albuminuria.•Use the term “risk categories” to describe combinations of the G (GFR) and A (albuminuria) categories from the KDIGO heat map (see Supplementary Fig. S1).•Use specific terms, such as “GFR,” “tubular secretion,” “tubular reabsorption,” “albuminuria,” and “proteinuria,” rather than general terms, such as “abnormal” or “reduced” kidney function, damage, or injury, when possible. Because kidney function comprises several functional categories, including excretory, endocrine, and metabolic functions, it should be described as specifically as possible. GFR is closely linked with the excretory function, but it should not be used as a synonym, because tubular reabsorption and excretion also contribute to excretory function.•When referring to “decreased or decreasing GFR,” avoid the use of different, poorly defined terms such as “impaired kidney function,” “renal insufficiency,” “renal dysfunction,” “renal impairment,” “worsening kidney function,” and “kidney function decline.”•When referring to GFR, use descriptive abbreviations (mGFR for measured GFR and eGFR for estimated GFR, with specific notation based on the endogenous filtration markers used (e.g., eGFRcr, eGFRcys, and eGFRcr-cys). Additional detail can be given in the methods. For mGFR, the methods should describe the exogenous filtration marker (e.g., inulin, iothalamate, iohexol) and clearance method (urinary clearance, plasma clearance). For eGFR, the methods should describe the estimating equation used (CKD-EPI; MDRD Study).•Avoid referring to “albuminuria” or “proteinuria” as “decreased kidney function.” Albuminuria and proteinuria are markers of kidney damage, rather than measures of kidney function.•When referring to albuminuria or proteinuria, avoid the terms “microalbuminuria” and “macroalbuminuria/clinical proteinuria.” Use the terms “moderately increased” or “severely increased” instead.•When referring to albuminuria and proteinuria, use descriptive abbreviations, such as “urine albumin or protein excretion rates (AER and PER)” and “urine albumin–creatinine or protein–creatinine ratios (ACR and PCR).”ACR, albumin-creatinine ratio; AER, albumin excretion rate; AKD, acute kidney diseases and disorders; AKI, acute kidney injury; CKD, chronic kidney disease; CKD-EPI, CKD Epidemiology Collaboration; eGFR, estimated glomerular filtration rate; eGFRcr, estimated glomerular filtration rate derived from creatinine; eGFRcr-cys, estimated glomerular filtration rate derived from creatinine and cystatin C; eGFRcys, estimated glomerular filtration rate derived from cystatin C; ESKD, end-stage kidney disease; ESRD, end-stage renal disease; GFR, glomerular filtration rate; KDIGO, Kidney Disease: Improving Global Outcomes; KRT, kidney replacement of in Renal mGFR, measured glomerular filtration rate; Institute of Diabetes and Digestive and Kidney ratio; protein excretion rate; renal replacement US, United in a Table Kidney and Disease terms to describe kidney function and kidney disease, and and measures style will dictate and when to abbreviate to Kidney and term “kidney” should be used when describing kidney disease and kidney function, with the “nephro-” in the setting of specific functions, or the of acute kidney diseases and disorders and chronic kidney disease, in the setting of specific the of different and of the should not be with glomerular filtration rate (GFR) function when describing specific functions, renal renal kidney term to of kidney function that should be kidney term to of kidney function that should be insufficiency, kidney function in with kidney failure KRT; further is rate, Although it is used in the setting of dialysis, this term could be used to to kidney function in kidney renal function the of different and of the by and markers of injury and structure when describing specific within the such as kidney term to of kidney structure that should be kidney term to of kidney structure that should be of kidney of AKI, AKD, and CKD should be possible. may be or for ascertainment and of should be should not be inferred only from presence of condition as Kidney < 15 ml/min per 1.73 m2 or treatment by further is failure end-stage renal disease end-stage kidney disease renal disease; insufficiency, kidney injury stage may be revised by KDIGO AKI stage duration ≤ 3 renal renal disease; insufficiency, Kidney duration > 3 renal chronic renal disease; chronic chronic insufficiency, kidney and preferred or symptoms and with symptoms and would be with of symptoms and with kidney failure not a for Kidney replacement may be revised by KDIGO AKD consensus is includes dialysis and replacement stage stage 3 by by ESRD, CKD vs. refers to dialysis for CKD, and may also be to as refers to dialysis for dialysis, acute dialysis terms acute and chronic to duration of kidney disease rather than duration of dialysis and dialysis or or Kidney ESRD, kidney or kidney Kidney failure with replacement by dialysis or CKD for both should be ESRD, Kidney failure without replacement without is KRT is not vs. not ESRD, kidney failure comprehensive is definition is comprehensive is comprehensive care is not vs. not Kidney and (AKD) and Kidney duration ≤ 3 different from recognition of renal failure acute renal kidney may be revised by KDIGO AKD consensus AKI, or GFR < 60 ml/min per 1.73 or markers of kidney damage for ≤ 3 months, or in GFR by or in by for ≤3 kidney definition is a of for > in by in or by in 1 classification by and stage preferred rather than stage a patient with AKI stage 3 to classification to all AKI including and KDIGO classification definition only to with stage creatinine stage creatinine stage creatinine Chronic Kidney Disease duration >3 renal failure insufficiency, GFR < 60 ml/min per 1.73 m2 or markers of kidney damage for >3 insufficiency, classification by GFR and albuminuria for of G and A For a patient with CKD to or a with CKD of that CKD classification is only to with CKD, so a patient could not be classified as “CKD there was no other of kidney CKD stage description preferred rather than G CKD without without of not dialysis or CKD, to heat map in Supplementary Fig. on the outcome CKD CKD to CKD to CKD to CKD to to GFR or not There is not yet consensus on use of specific terms to describe the (e.g., or rate of Use of specific terms should be defined in may be GFR may for other which may not be considered as CKD to improving GFR or on disease. Use of specific terms should be defined in Kidney to with or without kidney disease; and measures may improve filtration rate and and creatinine clearance are not filtration be per 1.73 m2 or glomerular filtration methods and exogenous filtration markers should be in methods glomerular filtration (e.g., and MDRD and filtration markers (e.g., creatinine and cystatin should be in methods glomerular filtration rate; using using cystatin using creatinine and cystatin be be per 1.73 m2 or methods and markers should be in methods using using using and creatinine (e.g., and markers should be in methods using use in describing GFR level of the presence or absence of kidney disease; GFR are ml/min per 1.73 m2 for categories can be (e.g., to increased ml/min per 1.73 ml/min per 1.73 m2 ml/min per 1.73 ml/min per 1.73 m2 ml/min per 1.73 m2 Kidney < 15 ml/min per 1.73 m2 or by dialysis of is generally but not If this term is used as an or the GFR be defined (e.g., ml/min per 1.73 GFR of GFR is generally as the between and function and vs. vs. as albumin albumin excretion for should be in of may or albumin-creatinine or for or of for should be in proteinuria, proteinuria protein protein excretion for should be in of may or or for or of for should be in and proteinuria use in describing albuminuria or proteinuria level of the presence or absence of kidney disease < < increased to increased to < < < < increased increased > > > > clinical proteinuria, proteinuria may be revised by KDIGO > > > > with or without as by the presence of and in function is to rate, clearance, or to is to rate, clearance, or to of of albumin-creatinine ratio; AER, albumin excretion rate; AKD, acute kidney diseases and disorders; AKI, acute kidney injury; Kidney acute renal acute renal acute tubular GFR and albuminuria CKD, chronic kidney disease; CKD-EPI, CKD Epidemiology Collaboration; kidney eGFR, estimated glomerular filtration rate; ESKD, end-stage kidney disease; end-stage kidney ESRD, end-stage renal disease; end-stage renal GFR, glomerular filtration rate; KDIGO, Kidney Disease: Improving Global Outcomes; kidney failure with replacement KRT, kidney replacement kidney of in Renal mGFR, measured ratio; protein excretion rate; renal disease; renal of kidney function, and kidney disease; renal replacement creatinine; tubular tubular style will dictate and when to abbreviate may be revised by KDIGO AKI may be revised by KDIGO AKD consensus may be revised by KDIGO in a albumin-creatinine ratio; AER, albumin excretion rate; AKD, acute kidney diseases and disorders; AKI, acute kidney injury; CKD, chronic kidney disease; CKD-EPI, CKD Epidemiology Collaboration; eGFR, estimated glomerular filtration rate; eGFRcr, estimated glomerular filtration rate derived from creatinine; eGFRcr-cys, estimated glomerular filtration rate derived from creatinine and cystatin C; eGFRcys, estimated glomerular filtration rate derived from cystatin C; ESKD, end-stage kidney disease; ESRD, end-stage renal disease; GFR, glomerular filtration rate; KDIGO, Kidney Disease: Improving Global Outcomes; KRT, kidney replacement of in Renal mGFR, measured glomerular filtration rate; Institute of Diabetes and Digestive and Kidney ratio; protein excretion rate; renal replacement US, United albumin-creatinine ratio; AER, albumin excretion rate; AKD, acute kidney diseases and disorders; AKI, acute kidney injury; Kidney acute renal acute renal acute tubular GFR and albuminuria CKD, chronic kidney disease; CKD-EPI, CKD Epidemiology Collaboration; kidney eGFR, estimated glomerular filtration rate; ESKD, end-stage kidney disease; end-stage kidney ESRD, end-stage renal disease; end-stage renal GFR, glomerular filtration rate; 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