1 Definition and classification
1.1 Definition
Chronic kidney disease is a persistent disorder in which kidney structure or function is abnormal for at least three months and the impairment has implications for health. The kidneys lose filtering capacity gradually, so waste products, salt, water, and other substances are not removed as efficiently. The condition may exist with or without a marked fall in filtration rate, especially when there are signs of kidney damage such as persistent protein in the urine, structural abnormalities, or pathologic findings.
1.2 Staging systems
Chronic kidney disease is classified by both the level of kidney filtration and the degree of kidney damage. This combined approach helps estimate prognosis, guide monitoring, and inform treatment choices. Staging is usually based on laboratory data rather than symptoms, because many people remain asymptomatic until later stages.
1.2.1 Estimated glomerular filtration rate
Estimated glomerular filtration rate is a calculated measure of how much blood the kidneys filter each minute. It is derived from serum creatinine and other variables such as age and sex. Lower values indicate reduced kidney function and are grouped into stages ranging from mildly decreased filtration to kidney failure. Repeated measurements are used because a single value can be affected by hydration, muscle mass, and temporary illness.
1.2.2 Albuminuria categories
Albuminuria refers to the abnormal loss of albumin in the urine, a sign of damage to the kidney’s filtering units. Categories are typically based on the urine albumin-to-creatinine ratio. Higher albumin levels generally indicate greater kidney injury and a higher risk of progression and cardiovascular complications. Albuminuria also provides information beyond filtration rate, since some people have substantial kidney damage despite only modestly reduced estimated glomerular filtration rate.
1.3 Acute kidney injury versus chronic kidney disease
Acute kidney injury develops over hours to days and is often caused by sudden illness, reduced blood flow, obstruction, or toxic exposure. Chronic kidney disease evolves over months to years and reflects lasting loss of kidney function or structure. The two conditions may overlap, and acute injury can occur on top of chronic disease. Distinguishing them is important because acute problems may be reversible, whereas chronic disease usually requires long-term management.
2 Causes and risk factors
Chronic kidney disease has many causes, but a few account for most cases worldwide. Long-standing metabolic and vascular conditions are especially important, although inherited disorders, inflammatory diseases, and medication-related injury can also contribute. Risk increases with older age, family history, obesity, smoking, and prior episodes of kidney injury.
2.1 Diabetes mellitus
Diabetes is a leading cause of chronic kidney disease. Persistently elevated blood glucose damages small blood vessels in the kidneys and alters the filtration barrier. Over time, this can lead to protein leakage, declining filtration, and progressive scarring. The risk rises with poor glycemic control and longer duration of disease.
2.2 Hypertension
High blood pressure both causes and worsens kidney disease. Elevated pressure injures renal blood vessels and accelerates scarring within the filtering units. As kidney function declines, blood pressure often becomes harder to control, creating a reinforcing cycle. This relationship makes blood pressure management central to prevention and treatment.
2.3 Glomerular diseases
Glomerular diseases are disorders that directly affect the glomeruli, the kidney’s filtration structures. They may be inflammatory, immune-mediated, or driven by abnormal deposits. Examples include various forms of glomerulonephritis and nephrotic syndromes. These disorders can cause blood or protein in the urine, reduced filtration, and eventual chronic impairment.
2.4 Tubulointerstitial diseases
Tubulointerstitial diseases primarily affect the kidney tubules and surrounding tissue. Causes include recurrent infection, obstruction, autoimmune disease, and chronic exposure to harmful agents. Because the tubules are responsible for concentrating urine and maintaining electrolyte balance, injury in this region can lead to impaired urine handling, salt wasting, or gradual loss of function.
2.5 Polycystic and inherited kidney disorders
Some kidney diseases are inherited and lead to structural abnormalities from birth or early adulthood. Polycystic kidney disease is a well-known example, characterized by the growth of fluid-filled cysts that enlarge the kidneys and displace normal tissue. Other genetic disorders may affect collagen, transport proteins, or other structural components needed for normal renal function.
2.6 Medication and toxin exposure
Certain medications and toxins can damage the kidneys when used repeatedly, in high doses, or in susceptible individuals. Nonsteroidal anti-inflammatory drugs, some antibiotics, contrast agents, and lithium are among the better-known contributors. Environmental toxins and herbal products may also play a role. The effect may be direct injury, altered blood flow, or chronic interstitial scarring.
3 Pathophysiology
The underlying biology of chronic kidney disease involves loss of functioning nephrons, compensatory changes in the remaining units, and gradual tissue scarring. These processes eventually impair filtration, hormone production, and regulation of fluids and electrolytes. As damage advances, kidney disease also affects the cardiovascular system and other organs.
3.1 Nephron loss and hyperfiltration
When nephrons are destroyed, the remaining units compensate by filtering more blood. This hyperfiltration helps preserve overall kidney function at first, but it also increases mechanical stress within the glomeruli. Over time, this adaptation can accelerate damage and promote further nephron loss.
3.2 Fibrosis and scarring
Persistent injury triggers inflammation and the deposition of fibrous tissue. Fibrosis replaces normal kidney architecture with scar tissue that cannot filter blood effectively. Because scarring is often irreversible, the process leads to a gradual and permanent decline in function.
3.3 Proteinuria and kidney damage progression
Protein in the urine is not only a marker of injury but also a contributor to progression. Filtered proteins can irritate tubular cells and amplify inflammatory pathways. The presence of proteinuria often signals more active disease and a greater risk of decline, making it an important therapeutic target.
3.4 Cardiovascular interactions
Kidney disease and cardiovascular disease are closely linked. Impaired kidney function promotes hypertension, fluid overload, vascular calcification, and metabolic disturbances, all of which strain the heart and blood vessels. In return, cardiovascular problems can reduce kidney perfusion and worsen renal injury. This bidirectional relationship is a major reason for the high complication burden associated with chronic kidney disease.
4 Signs and symptoms
Symptoms often develop slowly and may be absent until kidney function is significantly reduced. Many findings are nonspecific, which is why laboratory testing is essential for diagnosis. When symptoms do appear, they often reflect fluid imbalance, toxin buildup, or reduced production of erythropoietin and other kidney-related hormones.
4.1 Early-stage disease
Early chronic kidney disease is frequently silent. Some individuals may have mild fatigue, subtle urinary abnormalities, or elevated blood pressure, but many feel well. Because outward signs are limited, the condition is commonly found during routine screening or evaluation of another illness.
4.2 Fluid retention
As salt and water excretion decline, fluid can accumulate in the body. This may cause swelling in the ankles, puffiness around the eyes, weight gain, or shortness of breath if fluid builds in the lungs. Fluid retention often becomes more noticeable as the disease advances.
4.3 Urinary changes
Urine output may become foamy when protein is present, or it may change in quantity or frequency. Some people notice nocturia, meaning increased urination at night. In later stages, urine may be less concentrated, and the kidneys may have difficulty conserving water or electrolytes.
4.4 Fatigue and weakness
Fatigue is common and may result from anemia, toxin buildup, poor sleep, or metabolic imbalance. Weakness can accompany reduced oxygen delivery, electrolyte abnormalities, and general deconditioning. These symptoms are not specific but often become more prominent as disease progresses.
4.5 Advanced uremic symptoms
Advanced disease can produce uremic symptoms caused by the accumulation of metabolic waste. These may include nausea, poor appetite, metallic taste, itching, confusion, restlessness, and difficulty concentrating. In severe cases, the buildup of toxins affects multiple organ systems and requires urgent treatment.
5 Diagnosis
Diagnosis relies on evidence of reduced kidney function, kidney damage, or both, persisting over time. Clinicians typically combine history, physical examination, blood and urine testing, imaging, and sometimes biopsy. The goal is to identify the cause, determine severity, and assess complications.
5.1 Medical history and physical examination
History-taking focuses on diabetes, hypertension, urinary abnormalities, family history, medication use, prior kidney injury, and systemic disease. Physical examination may reveal edema, elevated blood pressure, signs of volume overload, or evidence of an underlying disorder. Because the findings can be subtle, the exam is often supplemented by laboratory evaluation.
5.2 Blood tests
Blood tests are central to assessing kidney function and related complications. They help estimate filtration, identify electrolyte abnormalities, and detect anemia or metabolic disturbances. Results are interpreted in context and often repeated to confirm chronicity.
5.2.1 Serum creatinine
Serum creatinine is a waste product from muscle metabolism that rises when filtration declines. Although useful, it is influenced by muscle mass, diet, and some medications. A normal creatinine value does not always exclude kidney disease, particularly in people with low muscle mass.
5.2.2 Estimated glomerular filtration rate
Estimated glomerular filtration rate is derived from serum creatinine and provides a more useful indicator of kidney function than creatinine alone. It is used to stage disease, monitor progression, and adjust medication dosing. Serial measurement helps show whether function is stable or declining.
5.3 Urine tests
Urine testing detects kidney damage that may not be evident in blood work. It can reveal protein, blood, casts, or other abnormalities suggesting specific patterns of injury. Persistent findings are especially informative when repeated over time.
5.3.1 Urine albumin-to-creatinine ratio
The urine albumin-to-creatinine ratio estimates how much albumin is lost in the urine while correcting for urine concentration. It is a practical screening and monitoring tool. Elevated values are associated with higher risk of progression and cardiovascular events.
5.3.2 Urinalysis and sediment examination
Urinalysis can show blood, protein, glucose, leukocytes, or crystals. Microscopic sediment examination may identify red blood cell casts, white blood cell casts, or other clues to the cause of disease. These findings help distinguish glomerular, tubular, infectious, or obstructive processes.
5.4 Imaging studies
Ultrasound is commonly used to assess kidney size, shape, and obstruction. Small kidneys often suggest chronic irreversible damage, while enlarged kidneys may point to specific disorders such as polycystic disease or infiltrative conditions. Other imaging studies may be used when structural detail is needed.
5.5 Kidney biopsy
Kidney biopsy involves obtaining a small sample of tissue for microscopic examination. It is performed when the cause is uncertain, when diagnosis will change treatment, or when unusual features are present. Biopsy can distinguish active inflammation from chronic scarring and may reveal specific diseases not identifiable by other tests.
5.6 Differential diagnosis
Other conditions can mimic chronic kidney disease or coexist with it. These include acute kidney injury, urinary obstruction, dehydration, heart failure, and disorders causing transient changes in creatinine. Distinguishing chronic disease from reversible causes is important for appropriate management.
6 Complications
As kidney function declines, complications extend beyond filtration failure. The kidneys also regulate red blood cell production, mineral metabolism, acid-base balance, and fluid status. These disturbances contribute to symptoms and increase long-term health risks.
6.1 Anemia
Anemia is common because diseased kidneys produce less erythropoietin, a hormone that stimulates red blood cell formation. Reduced iron availability and chronic inflammation can also contribute. Anemia may cause fatigue, reduced exercise tolerance, and shortness of breath.
6.2 Mineral and bone disorders
Chronic kidney disease disrupts calcium, phosphorus, vitamin D, and parathyroid hormone balance. This can weaken bones and promote abnormal mineral deposition in blood vessels and soft tissues. The resulting disorder is often referred to as chronic kidney disease–mineral and bone disorder.
6.3 Hyperkalemia
Hyperkalemia is an elevated potassium level in the blood. It can occur when the kidneys cannot excrete potassium efficiently, especially in advanced disease or during treatment with certain medications. Severe hyperkalemia can disturb cardiac rhythm and requires prompt attention.
6.4 Metabolic acidosis
When kidneys cannot remove acid effectively, the body may develop metabolic acidosis. This disturbance can contribute to bone loss, muscle wasting, and faster disease progression. It is more likely when filtration is substantially reduced.
6.5 Hypertension and volume overload
Fluid retention and vascular changes often make blood pressure difficult to control. Excess volume can worsen edema, raise cardiac workload, and intensify symptoms such as breathlessness. Hypertension then further injures the kidneys, reinforcing progression.
6.6 Cardiovascular disease
People with chronic kidney disease have a high risk of coronary disease, stroke, heart failure, and vascular calcification. Shared risk factors such as diabetes and hypertension play a role, but kidney-related metabolic changes also add risk. Cardiovascular disease is a leading cause of death in this population.
6.7 Uremia
Uremia refers to the clinical syndrome that results from severe accumulation of waste products and other metabolic derangements. It can affect the nervous system, digestive tract, skin, and heart. Severe uremia is a major indication for kidney replacement therapy.
7 Management
Management aims to slow loss of kidney function, control symptoms, and reduce the likelihood of complications. Treatment is tailored to the cause, stage, and comorbid conditions. Ongoing follow-up is important because needs change as disease advances.
7.1 General treatment goals
General goals include preserving kidney function, managing blood pressure, limiting proteinuria, correcting metabolic problems, and lowering cardiovascular risk. Treatment also focuses on avoiding nephrotoxic exposures and ensuring safe medication use. Patient education and regular monitoring are essential parts of care.
7.2 Blood pressure control
Blood pressure control is one of the most effective ways to slow progression. Targets depend on overall health, proteinuria, and tolerance of therapy. Monitoring at home or in clinic helps guide adjustments.
7.2.1 Renin-angiotensin system blockade
Angiotensin-converting enzyme inhibitors and angiotensin receptor blockers reduce intraglomerular pressure and proteinuria. They are often preferred when albuminuria is present. Kidney function and potassium must be monitored after starting or increasing these medications.
7.2.2 Lifestyle measures
Lifestyle measures include weight management, regular physical activity, smoking cessation, and limiting alcohol when appropriate. These steps can improve blood pressure and overall cardiovascular health. They are usually combined with medication rather than used alone.
7.3 Glycemic control in diabetes
For people with diabetes, careful glucose management helps reduce kidney injury and other vascular complications. Treatment is individualized to avoid both chronic hyperglycemia and dangerous hypoglycemia. Kidney function may affect the choice and dosing of glucose-lowering medications.
7.4 Dietary management
Dietary planning can reduce symptoms and help manage biochemical abnormalities. Recommendations vary by stage, laboratory findings, and nutritional status. Overly restrictive diets should be avoided if they lead to malnutrition.
7.4.1 Sodium restriction
Reducing sodium intake can help control blood pressure and edema. It may also improve the response to antihypertensive therapy and diuretics. Practical guidance usually focuses on limiting processed and packaged foods.
7.4.2 Protein intake
Moderate protein intake may reduce nitrogen waste and lessen kidney workload in some patients. However, excessive restriction can cause loss of muscle and poor nutrition. Dietary advice should be individualized, especially in advanced disease.
7.4.3 Potassium and phosphorus management
If potassium or phosphorus levels are elevated, intake may need to be adjusted. High-potassium foods and phosphorus-rich processed foods are common targets for modification. Diet changes should be based on laboratory results rather than broad restriction alone.
7.5 Diuretics and edema control
Diuretics help remove excess fluid and can relieve swelling and shortness of breath. They are often used when volume overload contributes to hypertension or symptoms. Response depends on kidney function, sodium intake, and the specific diuretic chosen.
7.6 Treatment of anemia
Anemia management may include iron replacement and, in selected cases, erythropoiesis-stimulating agents. The approach depends on the severity of anemia and the likely cause. Treatment aims to improve symptoms while avoiding excessive hemoglobin correction.
7.7 Management of mineral and bone disorder
This aspect of care may involve dietary phosphorus reduction, phosphate binders, vitamin D therapy, and control of parathyroid hormone abnormalities. The objective is to reduce bone disease and vascular complications. Monitoring calcium, phosphorus, and related hormones is important during treatment.
7.8 Management of metabolic complications
Metabolic issues such as acidosis, hyperkalemia, and dyslipidemia are treated according to severity and cause. Correcting these disturbances can improve well-being and reduce risk. Medication review is also essential, since some drugs worsen electrolyte or acid-base problems.
7.9 Slowing progression of kidney damage
Progression can be slowed by controlling blood pressure and glucose, reducing proteinuria, avoiding nephrotoxins, and treating underlying disease. Newer therapies have expanded the options for some patients, especially those with diabetes or albuminuria. Consistent follow-up and early intervention are key.
8 Kidney replacement therapy
Kidney replacement therapy is used when the kidneys can no longer maintain essential functions adequately. It includes dialysis and transplantation. The choice depends on medical suitability, patient preferences, and access to treatment.
8.1 Hemodialysis
Hemodialysis filters blood through a machine outside the body. It is typically performed several times per week in a center or sometimes at home. Vascular access, treatment time, and fluid removal are important practical considerations.
8.2 Peritoneal dialysis
Peritoneal dialysis uses the lining of the abdomen as a natural filter. A cleansing fluid is introduced into the abdominal cavity and then drained after waste products have moved into it. It can be done manually or with a machine, often allowing more flexibility in daily life.
8.3 Kidney transplantation
Kidney transplantation replaces a failed kidney with a healthy donor organ. It can offer better survival and quality of life than long-term dialysis for eligible patients. Lifelong follow-up and immunosuppressive medication are required to prevent rejection.
8.4 Indications for initiation
Kidney replacement therapy is started when symptoms or laboratory abnormalities indicate that kidney function is no longer sufficient. Common triggers include severe uremic symptoms, refractory hyperkalemia, persistent fluid overload, worsening acidosis, or profound decline in filtration. The decision is based on the overall clinical picture rather than a single laboratory value.
9 Prognosis
The outlook in chronic kidney disease varies widely. Some people remain stable for years, while others experience rapid decline. Prognosis depends on the cause, stage, rate of progression, and associated health conditions.
9.1 Disease progression
Progression is usually gradual but can accelerate after acute illness, uncontrolled blood pressure, recurrent proteinuria, or continued exposure to injury. Serial measurement of filtration and albuminuria is used to track change. Earlier stages often progress more slowly than advanced disease.
9.2 Predictors of outcome
Important predictors include estimated glomerular filtration rate, albuminuria, blood pressure control, diabetes status, and the presence of structural or genetic disease. Age, smoking, and prior cardiovascular disease also influence risk. Greater proteinuria and lower filtration generally indicate worse prognosis.
9.3 Mortality and cardiovascular risk
Cardiovascular complications account for a large share of adverse outcomes. Even moderate kidney impairment raises the likelihood of heart and vascular events. As kidney function declines, overall mortality rises, especially when diabetes, hypertension, and heart disease are also present.
10 Prevention
Prevention focuses on reducing the development of kidney injury and slowing worsening in people who already have early disease. Effective prevention requires attention to metabolic, vascular, and medication-related risks. Public health measures and clinical screening both contribute.
10.1 Primary prevention
Primary prevention includes control of diabetes and hypertension, healthy body weight, avoidance of smoking, and prudent use of nephrotoxic medications. Preventing acute kidney injury may also lower long-term risk. Good cardiovascular health supports kidney health as well.
10.2 Screening of at-risk groups
People with diabetes, hypertension, family history of kidney disease, cardiovascular disease, or prior kidney injury may benefit from routine testing. Screening generally includes serum creatinine, estimated glomerular filtration rate, and urine albumin measurement. Early detection makes intervention more effective.
10.3 Secondary prevention and follow-up
For established chronic kidney disease, regular follow-up aims to slow progression and catch complications early. This includes monitoring blood pressure, kidney function, urine protein, electrolytes, and anemia markers. Medication review and patient education are recurring parts of care.
11 Epidemiology
Chronic kidney disease is a major global health problem and a common cause of disability and premature death. Its burden is influenced by aging populations, diabetes, hypertension, and access to healthcare. Prevalence and outcomes vary by region and population group.
11.1 Global prevalence
The condition affects a substantial proportion of adults worldwide, with many cases remaining undiagnosed. Mild to moderate stages are much more common than kidney failure. Population studies often find higher prevalence in settings with increasing rates of diabetes and hypertension.
11.2 Age and sex distribution
Risk rises with age, partly because kidney reserve declines over time and chronic illnesses become more common. Men and women may show different patterns depending on cause, access to care, and comorbidity profiles. In many studies, older adults account for a large share of diagnosed cases.
11.3 Population risk patterns
Risk is higher in people with diabetes, hypertension, obesity, cardiovascular disease, and a family history of kidney disorders. Social and economic factors also influence exposure to risk and access to diagnosis. Occupational or environmental toxin exposure may contribute in some communities.
12 History
Understanding of chronic kidney disease evolved gradually as medicine advanced from symptom-based descriptions to laboratory-defined staging. Improvements in chemistry testing, imaging, and pathology made it possible to identify kidney impairment earlier and classify it more precisely. Treatment also changed from supportive care alone to targeted therapy and kidney replacement options.
12.1 Development of the concept
Early descriptions of kidney disease focused on obvious symptoms such as edema and urinary changes. As pathology and physiology developed, clinicians recognized that chronic loss of renal function could occur silently over time. The concept of long-standing kidney impairment became more clearly defined with the growth of laboratory medicine.
12.2 Advances in diagnosis and staging
The introduction of serum creatinine testing, urine protein measurement, and later estimated glomerular filtration rate transformed diagnosis. Standard staging systems allowed clinicians to compare patients and estimate risk more accurately. Albuminuria became recognized as a key marker of both kidney damage and prognosis.
12.3 Evolution of treatment approaches
Treatment initially centered on managing symptoms and preparing for dialysis when failure became severe. Later, blood pressure control, renin-angiotensin system blockade, and better diabetes management improved outcomes for many patients. Kidney transplantation and home-based dialysis expanded the range of long-term options.
13 Research directions
Current research aims to improve early detection, prevent progression, and replace lost kidney function more effectively. Studies include biomarker discovery, new drug development, and regenerative strategies. Better understanding of individual disease mechanisms may allow more personalized care.
13.1 Biomarkers
Researchers are seeking markers that detect kidney injury earlier than creatinine or albumin alone. Promising biomarkers may identify specific pathways such as inflammation, fibrosis, or tubular injury. Such tools could improve risk prediction and help match patients with targeted therapies.
13.2 Novel therapies
New treatments are being developed to slow progression, reduce proteinuria, and protect cardiovascular health. Some focus on metabolic pathways, inflammation, or fibrosis rather than only blood pressure control. The goal is to preserve kidney function more effectively and for longer periods.
13.3 Regenerative and transplant research
Regenerative medicine explores ways to repair damaged kidney tissue or grow replacement structures. Transplant research includes strategies to improve organ preservation, reduce rejection, and expand donor availability. These efforts aim to address the shortage of replacement kidneys and improve long-term outcomes.