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 Figure 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)” |
Preferred term | Suggested abbreviationsa | Rationale/explanation | Terms to avoid |
---|---|---|---|
Part 1. Kidney function and disease | The term “kidney” should be used preferentially when describing kidney disease and kidney function, with exceptions | “Renal,” the prefix “nephro-” (except in the setting of specific functions, diseases, or syndromes; see below) | |
Kidney disease | Reflects the entirety of acute kidney diseases and disorders and chronic kidney disease | Renal disease, nephropathy (except in the setting of specific diseases, e.g., membranous nephropathy) | |
Kidney function | Reflects the entirety of different and complex physiological functions of the kidney; should not be equated with glomerular filtration rate (GFR) only | Renal function (except when describing specific functions, e.g., renal acidification, renal concentrating mechanism) | |
Normal kidney function | General term applicable to various aspects of kidney function that should be specified | ||
Abnormal kidney function | General term applicable to various aspects of kidney function that should be specified | Renal/kidney impairment, insufficiency, dysfunction; azotemia | |
Residual kidney function | RKF | Kidney function in people with kidney failure receiving KRT; further specification is required, e.g., urine flow rate, solute clearance. Although it is usually used in the setting of dialysis, this term could be used to refer to native kidney function in kidney transplant recipients | Residual renal function (RRF) |
Kidney structure | Reflects the entirety of different and complex structures of the kidney, ascertained by imaging and markers of injury and damage | Renal structure (except when describing specific structures within the kidney, such as artery, vein, capsule, parenchyma, cortex, medulla, glomeruli, tubules, interstitium, cysts, tumors) | |
Normal kidney structure | General term applicable to various aspects of kidney structure that should be specified | ||
Abnormal kidney structure | General term applicable to various aspects of kidney structure that should be specified | ||
Causes of kidney disease | Cause of AKI, AKD, and CKD should be indicated whenever possible. Cause may be known, presumed, or unknown. Method for ascertainment and attribution of cause should be specified | Cause should not be inferred only from presence of comorbid condition (such as diabetes) | |
Part 2. Kidney failure | GFR < 15 ml/min per 1.73 m2 or treatment by dialysis; further specification is required; see below | Renal failure (RF); end-stage renal disease (ESRD); end-stage kidney disease (ESKD); renal disease; nephropathy; renal/kidney impairment, insufficiency, dysfunction; azotemia | |
Duration | Specification preferred | ||
Acute kidney injury stage 3b | AKI stage 3 | Disease duration ≤ 3 months | Acute renal failure; renal disease; nephropathy; renal/kidney impairment, insufficiency, dysfunction; azotemia; uremia |
Kidney failure | KF | Disease duration > 3 months | Chronic renal failure; chronic renal disease; chronic nephropathy; chronic renal/kidney impairment, insufficiency, dysfunction; azotemia; uremia; irreversible kidney failure |
Symptoms and signs | Specification preferred (with, without, or unknown symptoms and signs); with symptoms and signs would be synonymous with uremia | ||
Uremia/uremic syndrome | A syndrome consisting of symptoms and signs associated with kidney failure (does not indicate a causal role for urea) | ||
Treatment | Specification required | ||
Kidney replacement therapyc | KRT | Further specification is required; includes dialysis and transplantation | Renal replacement therapy (RRT) |
Dialysis | AKI stage 3D | AKI stage 3 treated by dialysis | AKI-D, dialysis-dependent AKI |
CKD G5D | CKD G5 treated by dialysis | ESKD, ESKF, ESRD, ESRF, dialysis-dependent CKD | |
Duration | Long-term vs. short-term: long-term refers to dialysis for CKD, and may also be referred to as maintenance dialysis; short-term refers to dialysis for AKD | Chronic dialysis, acute dialysis (the terms acute and chronic refer to duration of kidney disease rather than duration of dialysis treatment) | |
Modality and frequency | Modalities - Hemodialysis (HD) - Hemofiltration (HF) - Hemodiafiltration (HDF) - Peritoneal dialysis (PD, ambulatory or automated) Frequency - Continuous - Intermittent (short or prolonged) | ||
Kidney transplantation | CKD G1T–G5T | CKD G1–G5 after transplantation | ESKD, ESKF, ESRD, ESRF |
Donor source | Specify living donor kidney transplant/transplantation (LDKT) or deceased donor kidney transplant/transplantation (DDKT) | ||
Kidney failure with replacement therapy | KFRT | CKD G5 treated by dialysis or CKD G1–G5 after transplantation; for epidemiologic studies, both should be included | ESKD, ESKF, ESRD, ESRF |
Kidney failure without replacement therapy | CKD G5 without KRT | Further specification is preferred: specify whether KRT is not chosen vs. not available | ESKD, ESKF, ESRD, ESRF, untreated kidney failure |
With comprehensive conservative care | Further specification is preferred; definition is evolving | ||
Without comprehensive conservative care | Further specification is preferred: specify whether comprehensive conservative care is not chosen vs. not available | ||
Part 3. Acute Kidney Diseases and Disorders (AKD) and Acute Kidney Injury (AKI) | Disease duration ≤ 3 months; conceptually different from initial recognition of CKD | Acute renal failure (ARF); acute renal insufficiency (ARI) | |
Acute kidney diseases | AKDc | KDIGO definition: AKI, or GFR < 60 ml/min per 1.73 m2, or markers of kidney damage for ≤ 3 months, or decrease in GFR by ≥ 35% or increase in SCr by > 50% for ≤ 3 months | ARF, ARI |
Acute kidney injury | AKI | KDIGO definition (AKI is a subcategory of AKD): oliguria for > 6 h, rise in SCr by > 0.3 mg/dl in 2 days or by > 50% in 1 week | ARF, ARI |
AKI classification | KDIGO classification by cause and stage preferred rather than stage alone; e.g., a patient with AKI stage 3 due to ATN; classification applies to all AKI stages | Previous classifications, including RIFLE and AKIN (the KDIGO classification harmonized these prior definitions) | |
AKI stages | KDIGO definition (applicable only to people with AKI) | ||
AKI stage 1 | Serum creatinine and/or urine output criteria | ||
AKI stage 2 | Serum creatinine and/or urine output criteria | ||
AKI stage 3 | Serum creatinine and/or urine output criteria | ||
Part 4. Chronic Kidney Disease (CKD) | Disease duration > 3 months | Chronic renal failure (CRF); ESRD; renal/kidney impairment, insufficiency, dysfunction | |
CKD | KDIGO definition: GFR < 60 ml/min per 1.73 m2 or markers of kidney damage for > 3 months | CRF; ESRD; renal/kidney impairment, insufficiency, dysfunction | |
CKD classification | KDIGO CGA classification by cause, GFR category (G1–G5), and albuminuria category (A1–A3); see below for definitions of G and A categories. For example, a patient with CKD G1, A3 due to diabetes, or a cohort with CKD G4–G5, A1–A3 of any cause. Note that CKD classification is only applicable to people with CKD, so a patient could not be classified as “CKD G2, A1” if there was no other evidence of kidney damage | Mild, moderate, severe, early, advanced CKD; CKD stage 1–5 (complete description preferred rather than G category alone) | |
CKD without KRT | CKD without KRT | CKD G1–G5, A1–A3 of any cause, not receiving dialysis or transplantation | ND-CKD (non-dialysis CKD), NDD-CKD (non–dialysis-dependent CKD), predialysis CKD, pre-ESRD CKD |
CKD risk categories | KDIGO definitions (colors refer to heat map in Supplementary Figure S1) unless otherwise defined; risk depends on the outcome being considered | Mild, moderate, severe, early, advanced CKD | |
CKD risk category—low | Low risk | Refers to G1A1, G2A1 (green) | |
CKD risk category—moderately high | Moderate risk | Refers to G1A2, G2A2, G3aA1 (yellow) | |
CKD risk category—high | High risk | Refers to G1A3, G2A3, G3aA2, G3bA1 (orange) | |
CKD risk category—very high | Very high risk | Refers to G3aA3, G3bA2, G3bA3, G4A1, G4A2, G4A3, G5A1, G5A2, G5A3 (red) | |
CKD progression | Refers to worsening GFR or albuminuria. Other biomarkers not included. There is not yet consensus on use of specific terms to describe the timing (e.g., early, late) or rate (fast, slow) of progression. Use of specific terms should be defined in methods Further specification may be required: GFR decline may occur during therapy for other conditions, which may not be considered as CKD progression | ||
CKD remission | Refers to improving GFR or albuminuria. Criteria depend on disease. Use of specific terms should be defined in methods | ||
Part 5. Kidney Measures | Applies to people with or without kidney disease; consider measurement issues (methods) and variability (multiple measures may improve classification) | ||
Glomerular filtration rate and clearance | GFR and creatinine clearance are not synonymous | ||
Glomerular filtration rate | GFR | Units must be specified (ml/min per 1.73 m2 or ml/min) | |
Measured glomerular filtration rate | mGFR | Clearance methods and exogenous filtration markers should be noted separately in methods | |
Estimated glomerular filtration rate | eGFR | Estimating equations (e.g., CKD-EPI and MDRD Study) and filtration markers (e.g., creatinine and cystatin C) should be noted separately in methods | |
Estimated glomerular filtration rate; marker | eGFRcr | eGFR using creatinine | |
eGFRcys | eGFR using cystatin C | ||
eGFRcr-cys | eGFR using creatinine and cystatin C | ||
Clearance | Cl | Solute must be specified; units must be specified (ml/min per 1.73 m2 or ml/min) | |
Measured clearance | mCl | Clearance methods and markers should be noted separately in methods | |
Measured clearance; marker | mClUN | mCl using urea nitrogen | |
mClcr | mCl using creatinine | ||
mClUN-cr | mCl using urea nitrogen and creatinine | ||
Estimated clearance | eCl | Estimating equations (e.g., Cockcroft-Gault) and markers should be noted separately in methods | |
Estimated clearance; marker | eClcr | eCl using creatinine | |
GFR categories | For use in describing GFR level irrespective of the presence or absence of kidney disease; GFR units are ml/min per 1.73 m2 for these categories; multiple categories can be collapsed (e.g., G3–G5) | ||
Normal to increased GFR | G1 | GFR ≥ 90 ml/min per 1.73 m2 | |
Mildly reduced GFR | G2 | GFR 60–89 ml/min per 1.73 m2 | |
Moderately reduced GFR | G3a | GFR 45–59 ml/min per 1.73 m2 | |
G3b | GFR 30–44 ml/min per 1.73 m2 | ||
Severely reduced GFR | G4 | GFR 15–29 ml/min per 1.73 m2 | |
Kidney failure | G5 | GFR < 15 ml/min per 1.73 m2 or treated by dialysis | |
Hyperfiltration | The concept of hyperfiltration is generally accepted but not consistently defined. If this term is used as an exposure, outcome, or covariate, the GFR threshold must be defined (e.g., > 120 ml/min per 1.73 m2) | Renal hyperfiltration | |
GFR reserve | The concept of GFR reserve is generally accepted as the difference between stimulated and basal GFR | Renal function reserve | |
Albuminuria and proteinuria | Specify measurement conditions (spot vs. timed samples; quantitative vs. dipstick); differentiate non-albumin proteins as clinically indicated | ||
Albuminuria | Microalbuminuria, macroalbuminuria | ||
Urinary albumin concentration | |||
Urinary albumin excretion rate | AER | Requires timed urine collection; interval for urine collection should be noted separately in methods; unit of time may vary (hour or day) | |
Urinary albumin-creatinine ratio | ACR | From timed urine collection or spot urine collection; interval for timed urine collection, or time of day for spot urine collection, should be noted separately in methods | |
Proteinuria | Clinical proteinuria, overt proteinuria | ||
Urinary protein concentration | |||
Urinary protein excretion rate | PER | Requires timed urine collection; interval for urine collection should be noted separately in methods; unit of time may vary (hour or day) | |
Urinary protein-creatinine ratio | PCR | From timed urine collection or spot urine collection; interval for timed urine collection, or time of day for spot urine collection, should be noted separately in methods | |
Albuminuria and proteinuria categories | For use in describing albuminuria or proteinuria level irrespective of the presence or absence of kidney disease | ||
Normal | AER < 10 mg/day; ACR < 10 mg/g (< 1 mg/mmol) | Normoalbuminuria | |
Mildly increased (mild) | AER 10–29 mg/day; ACR 10–29 mg/g (1.0–2.9 mg/mmol) | ||
Normal to mildly increased (normal to mild) | A1 | AER < 30 mg/day; ACR < 30 mg/g (< 3 mg/mmol) PER < 150 mg/day; PCR < 150 mg/g (< 15 mg/mmol) | |
Moderately increased (moderate) | A2 | AER 30–300 mg/day; ACR 30–300 mg/g (3–30 mg/mmol) PER 150–500 mg/day; PCR 150–500 mg/g (15–50 mg/mmol) | Microalbuminuria |
Severely increased (severe) | A3 | AER > 300 mg/day; ACR > 300 mg/g (> 30 mg/mmol) PER > 500 mg/day; PCR > 500 mg/g (> 50 mg/mmol) | Macroalbuminuria, clinical proteinuria, overt proteinuria |
Nephrotic-range/syndromed | AER > 2200 mg/day; ACR > 2200 mg/g (> 220 mg/mmol) PER > 3500 mg/day; PCR > 3500 mg/g (> 350 mg/mmol) Specify with or without nephrotic syndrome, as noted by the presence of hypoalbuminemia (with edema and hyperlipidemia in most cases) | ||
Tubular function | |||
Tubular secretion | TS | Further specification is required to distinguish rate, clearance, or fraction (compared to filtered load) | |
Tubular reabsorption | TR | Further specification is required to distinguish rate, clearance, or fraction (compared to filtered load) | |
Fractional excretion, marker | FENa | FE of sodium | |
Fractional reabsorption, marker | FRNa | FR of sodium |