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  • Acceptability: Ability to generate enthusiasm and willingness to participate in the system.
  • Acute: Referring to a health effect, usually of rapid onset, brief, not prolonged.1
  • Acute coronary syndrome: Chest pain and other symptoms that happen because the heart does not get enough blood.3
  • Acute Kidney Injury (AKI): Formerly known as acute renal failure, AKI is characterized by a sudden decline in kidney function leading to buildup of waste products and disturbances in electrolytes and fluid balance. Common causes of AKI include sudden drop in blood flow to the kidneys (such as in severe infections called sepsis or in heavy blood loss), dehydration, toxicity from medications (such as certain antibiotics or pain medications), and blockage of urine outflow. In its most severe form, AKI requires the use of acute dialysis. AKI is recognized to be associated with greater risk of short-term and long-term death and adverse kidney outcomes.
  • Age-adjusted: With regard to an estimate, adjusted by age of the patient or participant. Age-adjusted estimates present the prevalence or risk independent of the effect of age.
  • Albumin: Any of numerous simple heat-coagulable water-soluble proteins that occur in blood plasma or serum, muscle, the whites of eggs, milk, and other animal substances, and in many plant tissues and fluids.2
  • Albuminuria: The presence of albumin in the urine often symptomatic of kidney disease.2

    Note: There are different thresholds and categories in defining albuminuria (see table below). Therefore, variability exists in how health care providers and researchers define, assess, and report albuminuria levels.

    Typical thresholds for defining proteinuria and albuminuria.

    Adapted from the National Kidney Foundation’s KDOQI guidelines for evaluation and stratification of chronic kidney disease (

    Typical thresholds for defining proteinuria and albuminuria

    Urine collection method



    Proteinuria or Macroalbuminuria

    Total Protein
    24-hour excretion <300 mg/dayN/A≥300 mg/day
    Spot urine dipstick<30 mg/dlN/A≥30 mg/dl
    Spot urine protein:creatinine ratio<200 mg/gN/A≥200 mg/g
    24-hour excretion<30 mg/day30-299 mg/day≥300 mg/day
    Spot urine albumin-specific dipstick<3 mg/dl≥3 mg/dlN/A
    Spot urine albumin:creatinine ratio
    Overall*<30 mg/g30-299 mg/g≥300 mg/g
    Men**<17 mg/g17-249 mg/g≥250 mg/g
    Women**<25 mg/g25-354 mg/g≥355 mg/g

    N/A, not applicable.

    *Use of the same cutoff for men and women is recommended by the American Diabetes Association guidelines but can result in higher prevalence in women.

    **Gender-specific cutoffs are from a single study (Mattix et al., 2002).

  • Allograft:

    A graft transplanted between genetically nonidentical individuals; synonymous with transplant.1

  • Analytic cohort: A sample of individuals used in an analysis.
  • Anemia: A condition that develops when your blood lacks enough healthy red blood cells which are the main transporters of oxygen to organs causing symptoms like fatigue.3
  • Angiotensin - converting enzyme inhibitors: Also known as ACE inhibitors; heart medications that widen or dilate your blood vessels to improve the amount of blood your heart pumps and lower blood pressure. ACE inhibitors also increase blood flow, which helps to decrease the amount of work your heart has to do. Some ACE inhibitors have been found to slow the process that leads to kidney damage in many people with type 2 diabetes.3
  • Angiotensin II Receptor Blockers (ARBs): Also known as ARBs, these are heart medications that block the angiotensin II hormone and widen or dilate blood vessels to improve blood flow. ARBs work very similarly to ACE inhibitors. 
  • APOL1: Studies have identified a gene on chromosome 22 encoding for apolipoprotein L1 (APOL1) which has been associated with a variety of nephropathies. Two variants of the gene, G1 and G2, are considered risk alleles and are associated with increased risk of CKD; these variants are common in people of African ancestry but have not been found in people with European ancestry.10
  • Atherosclerosis: Hardening of the arteries. Atherosclerosis occurs when plaque builds up inside the arteries, the blood vessels that carry oxygen-rich blood throughout your body. When atherosclerosis occurs in the arteries that supply blood to the heart, it is called coronary artery disease.3
  • Awareness: Having or showing realization, perception, or knowledge.2
  • Body Mass Index (BMI): An individual's weight in kilograms divided by his or her height in meters squared. It is a measureme of body fat.
  • Bone and mineral metabolism disorders: Disorders involving problems with hormonal regulation of the formation and turnover of bone in the body; broadly, these disorders may be grouped as osteoporosis, osteomalacia, hyperparathyroidism, Paget disease of bone, and developmental disorders of bone.
  • Burden: Load.2 In this report, referring to the amount of disease in a population, as measured by prevalence or incidence.
  • Cadaveric donor: Deceased donor of organs.
  • Cardiovascular: Relating to the heart and the blood vessels or the circulation.1
  • Cerebrovascular disease: Disease of the blood vessels, especially the arteries that supply the brain; usually caused by atherosclerosis and can lead to stroke.7
  • Chronic: Referring to a health-related state, lasting a long time; The U.S. National Center for Health Statistics defines a chronic condition as one of 3 months' duration or longer.1
  • Chronic kidney disease (CKD): Kidneys have the important job of filtering blood. They remove waste products and extra fluid and flush them from the body as urine. When the kidneys do not work properly, wastes build up in the blood and make people sick. Chronic kidney disease is caused by damage to the kidneys. There are a variety of causes of damage, in particular high blood pressure and high blood sugar (diabetes).3
  • CKD-EPI 2009 Formula:

    The 2009 CKD-EPI equation was a new glomerular filtration rate estimating equation, improving upon the MDRD equation. CKD-EPI stands for Chronic Kidney Disease Epidemiology Collaboration, a research group focused on developing glomerular filtration rate (GFR) estimating equations. The 2009 CKD EPI equation is as follows:

    Male: 141 * min(Scr/0.9, 1)-0.411 * max(Scr /0.9, 1)-1.209 * 0.993Age
    Female: 141 * min(Scr /0.7, 1)-0.329 * max(Scr /0.7, 1)-1.209 * 0.993Age * 1.018

    Male: 141 * min(Scr/0.9, 1)-0.411 * max(Scr /0.9, 1)-1.209 * 0.993Age * 1.159
    Female: 141 * min(Scr /0.7, 1)-0.329 * max(Scr /0.7, 1)-1.209 * 0.993Age * 1.018 * 1.159

    Scr is serum creatinine
    Min is the minimum of SCR/k and 1
    Max is the maximum of SCR/k and 1
    k=0.7 for females or 0.9 for males
    α=-0.241 for females or -0.302 for males

  • CKD-EPI 2021 Formula:

    The 2021 CKD-EPI formula is a new estimate of glomerular filtration rate that does not include race. 

    CKD-EPI stands for Chronic Kidney Disease Epidemiology Collaboration, a research group focused on developing glomerular filtration rate (GFR) estimating equations.The 2021 CKD EPI equation is as follows:

    Male: 142 * min(Scr/0.9, 1)-0.302 * max(Scr /0.9, 1)-1.209 * 0.9938Age
    Female: 142 * min(Scr /0.7, 1)-0.241 * max(Scr /0.7, 1)-1.209 * 0.9938Age * 1.012

    Scr is serum creatinine

  • Cohort: A group of individuals having a statistical factor (as age or class membership) in common in a demographic study.2
  • Comorbid: Existing simultaneously with and usually independently of another medical condition.2
  • Confidence interval: An interval within which the true value is expected to lie with a specified probability; e.g., a 95% confidence interval indicates that the true value lies within the interval specified with 95% probability.
  • Cost-effective: Economical in terms of tangible benefits produced by money spent.2
  • Covariate: Secondary variable that varies with the primary outcome and/or predictor in an analysis.
  • Creatinine: Creatinine is a waste product formed by the breakdown of a substance (creatine) important for converting food into energy (metabolism). The creatinine is filtered out of the blood by the kidneys and then passed out of the body in urine. Creatinine is produced at a steady rate and is affected very little by diet or normal physical activities. If the kidneys are damaged and cannot function normally, the amount of creatinine in the blood increases.3
  • Cross-sectional study: A study design where both exposure and disease outcome are determined simultaneously for each subject. (Gordis, 2009)
  • Crude: With regard to an estimate, not adjusted for any secondary variable.
  • Data quality: Degree to which data are complete and valid.
  • Defined denominator: Degree to which the target population can be clearly identified.
  • Denominator: The part of a fraction that is below the line and that functions as the divisor of the numerator.2
  • Diabetes mellitus: Diabetes is a chronic, lifelong condition that affects the body's ability to use the energy found in food. There are three major types of diabetes: type 1 diabetes, type 2 diabetes, and gestational diabetes. All types of diabetes mellitus have something in common. Normally, the body breaks down the sugars and carbohydrates you eat into a special sugar called glucose. Cells need insulin, a hormone, in your bloodstream in order to take in the glucose and use it for energy. With diabetes mellitus, either the body does not make enough insulin, or it cannot use the insulin it does produce. Since the cells cannot take in the glucose, it builds up in the blood. High levels of blood glucose can damage the tiny blood vessels in your kidneys, heart, eyes, or nervous system, increasing the risk of heart disease, stroke, kidney disease, blindness, and nerve damage to nerves in the feet.3

    Note: Unless otherwise specified, ‘diabetes’ refers to diabetes mellitus throughout the CKD Surveillance Report. In general, type 1 and type 2 diabetes were not distinguished in this report.

  • Diabetic nephropathy: Kidney disease that results from diabetes. Diabetic nephropathy is the number one cause of kidney failure. Almost one third of people with diabetes develop diabetic nephropathy.3
  • Dialysis: A process that does the work for the kidneys when a person has kidney failure. There are two types of dialysis: hemodialysis and peritoneal dialysis. Hemodialysis uses a man-made membrane called a dialyzer to clean the blood.  Peritoneal dialysis uses the lining of the belly, which is called the peritoneal membrane, to filter the blood.3
  • Dietary acid load (DAL):

    The metabolism of food in the body produces acids and bases of varying levels based on diet. The difference between the acids and bases is called the dietary acid load (DAL) or formally, net endogenous acid production (NEAP) and must be buffered or excreted by the body through respiration or urination in order to maintain an acid-base balance. 

  • Dyslipidemia: A condition marked by abnormal concentrations of lipids or lipoproteins (e.g. cholesterol) in the blood.2
  • Dysrhythmia: An abnormal rhythm, especially a disordered rhythm exhibited in a record of electrical activity of the brain or heart.2
  • End-stage renal disease (ESRD): The final stage of kidney failure (as that resulting from diabetes, chronic hypertension, or glomerulonephritis) that is marked by the complete or nearly complete irreversible loss of renal function.2
  • Enumerate: To ascertain the number of something, i.e.count.2
  • Epidemiology: The study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to control of health problems.1
  • Etiology: The cause or causes of a disease or abnormal condition.2
  • Expanded criteria donor (ECD): A donor that is not considered to be ideal or standard. Characteristics may include advanced donor age, prior infection with hepatitis B or hepatitis C, hypertension or diabetes mellitus, abnormal donor organ function, and non-heart-beating status of a deceased donor.4
  • Flexibility: Ability to look at new questions posed by research and accommodate changes in technology and reporting definitions.
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  • Glomerular filtration rate (GFR): Glomerular filtration is the process by which the kidneys filter the blood, removing excess wastes and fluids. GFR is a calculation that determines how well the blood is filtered by the kidneys, which is one way to measure remaining kidney function. GFR is usually estimated (estimated GFR or eGFR) using a mathematical formula that compares a person's size, age, sex, and race to serum creatinine levels. A GFR under 60 ml/min/1.73 m² may indicate kidney disease; the lower the GFR number, the worse the kidney function.3
  • Glomerulonephritis: A kidney disorder that causes inflammation in the small blood vessels of the kidney, which interferes with the kidney's ability to remove waste products from the blood. Glomerulonephritis can be caused by an infection, such as strep throat, or may be a complication of an autoimmune disease, such as lupus or rheumatoid arthritis. Untreated glomerulonephritis can cause severe chronic kidney disease.3
  • Glucose: A sugar found in the blood which is used by cells for energy.
  • Glycemia: The presence of glucose in the blood.2
  • Glycemic control: For people with diabetes, glycemic control refers to the maintenance of acceptable levels of blood sugar over a prolonged period, usually measured by hemoglobin A1c or fasting blood glucose.
  • Health care system: Complex of facilities, organizations, and trained personnel engaged in providing health care within a geographical area.
  • Health disparity: Refers to gaps in the quality of health and health care across racial, ethnic, and socioeconomic groups.5
  • Hemoglobin A1c (HbA1c) test: The hemoglobin A1c test, also called HbA1c, glycated hemoglobin test, or glycohemoglobin, is an important blood test used to determine how well diabetes is being controlled. Hemoglobin A1c provides an average of blood glucose control over a 6 to 12 week period and is used in conjunction with home blood glucose monitoring to appropriately treat diabetes.3
  • Hyperkalemia: An abnormally elevated level of potassium in the blood.7
  • Hypertension: High blood pressure, also called hypertension, is dangerous because it makes the heart work harder to pump blood to the body and it contributes to hardening of the arteries or atherosclerosis and the development of heart failure. There are usually no symptoms or signs of hypertension.3
  • Incidence: The rate of occurrence of new cases of a particular disease in a population being studied.2
  • Indicator: Precise measure specification; actual data elements that provide information about measures (e.g., eGFR or number of cigarettes smoked per day). Indicators within this report can be expressed as counts or means but are more often expressed as proportions or rates, which require specified numerators and denominators.
  • Inpatient: A patient who is hospitalized at least overnight for treatment.2
  • Interquartile Range (IQR): A measure of variability; the difference between the first quartile (25th percentile) and the third quartile (75th percentile) of an ordered dataset. 
  • Living donor: Living donor of organs.
  • Longitudinal: Involving the repeated observation or examination of a set of subjects over time with respect to one or more study variables.2
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  • Macroalbuminuria: Albuminuria characterized by a relatively high rate of urinary excretion of albumin, typically greater than 300 milligrams per 24-hour period (see Table 13.1 under definition of albuminuria).2
  • Managed care plan: A system that controls the financing and delivery of health services to members who are enrolled in a specific type of health care plan.6
  • Measure: A concept within a topic that addresses a broader topic of interest in quantifiable terms (e.g., prevalence of decreased kidney function to address CKD prevalence, or prevalence of current smoking to address CKD risk factors).
  • Microalbuminuria: Albuminuria characterized by a relatively low rate of urinary excretion of albumin, typically between 30 and 300 milligrams per 24-hour period (see Table 13.1 under definition of albuminuria).2
  • Modification of Diet in Renal Disease (MDRD) estimating equation:

    An equation used to estimate glomerular filtration rate (GFR) using serum creatinine and variables including age, gender, and race. Estimating equations are used to identify the stage of chronic kidney disease because serum creatinine levels alone cannot accurately reflect kidney function.

    MDRD equation: 

    GFR (mL/min/1.73 m2) = 175 × (calibrated serum creatinine in mg/dl)-1.154 × (age)-0.203 × (0.742 if female) × (1.212 if African American)

  • Morbidity: A diseased state or symptom; or the incidence of disease, the rate of sickness.2
  • Mortality: The number of deaths in a given time or place; or the proportion of deaths to population.2
  • Nephrologist: Medical doctors who specialize in the diagnosis and treatment of diseases of the kidney and urinary system, such as inflammation of the kidneys, chronic kidney disease, or cancer.3
  • Nephrology: A branch of medicine concerned with the kidneys.2
  • Nephrotic: Relating to, caused by, or consistent with kidney disease.1
  • Nephrotoxic drugs: Drugs that are poisonous to the kidney.2
  • Net endogenous acid production (NEAP): The metabolism of food in the body produces acids and bases of varying levels based on diet. The difference between the acids and bases is called the dietary acid load (DAL) or formally, net endogenous acid production (NEAP) and must be buffered or excreted by the body through respiration or urination in order to maintain an acid-base balance.

    See Dietary acid load

  • Numerator: The part of a fraction that is above the line and signifies the number to be divided by the denominator.2
  • Outcome: Something that follows as a result or consequence.2
  • Outpatient: A patient who is not hospitalized overnight but who visits a hospital, clinic, or associated facility for diagnosis or treatment.2
  • Parameter: A term used to define a characteristic of a population, in contrast to a sample from that population; e.g., the mean and standard deviation of a total population.1
  • Pathogenic : Causing disease or abnormality.1
  • Peripheral arterial disease: Narrowing or blockage of arteries that results in poor blood flow to the arms and legs; also known as PAD or peripheral vascular disease, PVD.
  • Population-based: The term population-based is defined as representative of a reference population for the topic of interest (e.g., for prevalence of CKD in the general U.S. population, representative of all individuals living in the United States; for prevalence of CKD in U.S. children, representative of all individuals <18 years of age in the United States).
  • Potassium-sparing diuretic: Diuretics that stimulate the kidneys to remove more water and salt (sodium) from the body without removing potassium; diuretics may also slightly dilate or widen blood vessels.3
  • Prevalence: The number of cases of a disease existing in a given population at a specific period of time (period prevalence) or at a particular moment in time (point prevalence).1
  • Prospective: Relating to or being a study (as of the incidence of disease) that starts with the present condition of a population of individuals and follows them into the future.2
  • Proteinuria: The presence of excess protein in the urine.2

    Note: There are different thresholds and categories in defining proteinuria (see table under definition of albuminuria). Therefore, variability exists in how health care providers and researchers define, assess, and report proteinuria levels.

  • Renal: Relating to, involving, affecting, or located in the region of the kidneys.2
  • Renal insufficiency: Reduced kidney function.
  • Representativeness: Degree to which information pertains to the general population; in this report the United States.
  • Restless Legs Syndrome (RLS): A neurological disorder that causes an individaul to feel an uncomfortable sensation in his/her legs leading to an urge to move them. Symptoms occur primarily at night, since lying down tends to activate the symptoms. The disorder affects both males and females, although the incidence is twice as high in females. Symptoms tend to worsen with age.
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  • Screen: To test or examine for the presence of something (as a disease).2
  • Sensitivity: Degree of capture of all events to monitor trends.
  • Serum: The fluid portion of the blood obtained after removal of the fibrin clot and blood cells, distinguished from the plasma in circulating blood.1
  • Serum Creatinine: A product of creatinine phosphate that is filtered from blood by the kidneys. Serum creatinine levels rise with decreased renal function
  • Simplicity: Ease of obtaining and working with data source system structure and operation.
  • Socioeconomic: Of, relating to, or involving a combination of social and economic factors (e.g., income or health insurance status).2
  • Special population: Population of interest that differs substantially in age, etiology, or other individual factor from the average CKD population and thus warrants independent surveillance.
  • Specificity: In clinical pathology and medical screening, the proportion of individuals with negative test results for the disease that the test is intended to reveal, i.e., true negative results as a proportion of the total of true negative and false-positive results.1
  • Stability: Ability to reliably operate and provide information when called upon.
  • Stages of Chronic Kidney Disease:

    Chronic Kidney Disease Stages8
    CKD Stage Description eGFR levels for ≥3 months
    Stage 1 Kidney damage with normal or increasing GFR eGFR ≥90 ml/min/1.73 m2
    Stage 2 Kidney damage with mild reduction in kidney function eGFR 60-89 ml/min/1.73 m2
    Stage 3 Moderate reduction in kidney function eGFR 30-59 ml/min/1.73 m2
    Stage 4 Severe reduction in kidney function eGFR 15-29 ml/min/1.73 m2
    Stage 5 Kidney Failure eGFR <15 ml/min/1.73 m2 (or dialysis)
    Chronic kidney disease is caused by damage to the kidneys. It is defined as either kidney damage or glomerular filtration rate (GFR) less than 60 mL/min/1.73 m2 for 3 months or greater. Kidney damage is defined by pathologic abnormalities or markers including abnormalities in imaging or urine or blood tests.

  • Standard Deviation Score (SDS): Indicate the number of standard deviations a data point is from the expected mean values. A postive SDS indicates that the data point is above the expected mean, while a negative SDS indicates that the data point is below the expected mean. 
  • Standard error: A measurement of the variance that is standardized to the size of the sample population.
  • Surveillance: The collection, collation, analysis, and dissemination of data; a type of observational study that involves continuous monitoring of disease occurrence within a population.1
  • Therapeutic: Relating to therapeutics or to the treatment, remediating, or curing of a disorder or disease.1
  • Timeliness: Duration of process from collecting information to delivering it to make health care changes.
  • Topic: A topic is defined as one of six broad areas important to capture in the CKD surveillance system (prevalence/incidence of CKD; awareness of CKD; burden of risk factors for CKD; health consequences of CKD; process and quality of care in CKD; and health care system capacity for CKD).
  • Transplant: To transfer (an organ or tissue) from one part or individual to another.2
  • Urine protein to creatinine ratio (UPCR): Ratio of urinary protein to creatinine used to quantify the amount of protein being excreted through urine and used to calculate proteinuria.

    See Albuminuria

  • Variance: A measure of the variation shown by a set of observations, defined as the sum of squares of deviations from the mean, divided by the number of degrees of freedom in the set of observations.1
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Definitions adapted in part or in full from the following sources:

1 Stedman’s Online Medical Dictionary:

2 Merriam-Webster Online Dictionary:

3 WedMD:

4 Scientific Registry of Transplant Recipients Online Glossary:

5 U.S. Department of Health and Human Services (HHS), Healthy People 2010: National Health Promotion and Disease Prevention Objectives, conference ed. in two vols (Washington, D.C., January 2000).

6 American Heart Association:

7 MedicineNet:

8 KDOQI Clinical Practice Guidelines for Chronic Kidney Disease: Evaluation, Classification, and Stratification:

9 Poupin N, Calvex J, Lassale C, et al. Impact of the diet on net endogenous acid production and acid–base balance. Clinical Nutrition. 2012;31: 313-321.

10 Parsa A, Kao WL, Xie D et al. APOL1 risk variants, race, and progression of chronic kidney disease. N Engl J Med. 2013; 369(23), 2183-2196.