OVERVIEW

What is kidney disease?

The kidneys are the urinary organs of the human body. Kidney disease refers to conditions where the filtration, reabsorption, excretion, and endocrine functions of the kidneys are impaired due to various causes.

Generally, kidney diseases include disorders of the glomeruli, renal tubules, and renal blood vessels caused by various factors. When kidney function declines significantly within a short period, it is termed acute kidney injury. If chronic kidney disease is not effectively controlled, it may progress to chronic kidney failure.

The kidneys produce urine, so kidney diseases often manifest as urinary abnormalities, such as hematuria, foamy urine, or reduced urine output. Other common symptoms include swelling of the eyelids and legs, anemia, and high blood pressure. In severe cases, the disease may affect other systems, leading to additional related symptoms.

Kidney diseases can result from many causes, including immune, infectious, and genetic factors. Patients with underlying conditions like hypertension or diabetes should manage their blood pressure and blood sugar levels carefully to protect kidney function and slow disease progression.

Is kidney disease common?

Kidney disease is a common condition. There are many types of kidney diseases, and their causes vary, including infections, immune disorders, and genetic factors.

Notably, with the rising prevalence of conditions like hypertension and diabetes, hypertensive kidney damage and diabetic nephropathy have become increasingly common.

What are the main structures of the kidney?

The primary functions of the kidneys are filtration and reabsorption, carried out by the basic functional unit called the nephron.

The nephron consists of the renal corpuscle and renal tubules. The renal corpuscle includes the glomerular capillaries and Bowman's capsule, while the renal tubules comprise the proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct.

In addition to nephrons, the kidneys contain the juxtaglomerular apparatus and renal interstitium. The former secretes substances like renin to regulate glomerular filtration rate.

What are the common types of kidney diseases?

Based on their causes, kidney diseases can be classified as primary, secondary, or hereditary.

Secondary kidney diseases refer to kidney damage caused by non-renal conditions, such as lupus nephritis, diabetic nephropathy, vasculitis-related kidney damage, hyperuricemic nephropathy, hepatitis B virus-associated nephritis, and myeloma kidney.

Primary kidney diseases are categorized by the affected site, including glomerular diseases, tubular diseases, and renal vascular diseases. Glomerular diseases can be further classified into various pathological types based on biopsy results.

Depending on the duration of kidney dysfunction, kidney diseases can be acute kidney injury (a rapid decline in kidney function with uremic symptoms) or chronic kidney failure (the end-stage outcome of progressive chronic kidney disease).

SYMPTOMS

What are the classifications of kidney diseases? What are their characteristics?

Kidney diseases encompass various types with different causes and clinical manifestations.

• Primary glomerular diseases primarily present with hematuria, proteinuria, edema, hypertension, and abnormal renal function. They can be classified into acute glomerulonephritis, rapidly progressive glomerulonephritis, IgA nephropathy, nephrotic syndrome, asymptomatic hematuria and/or proteinuria, and chronic glomerulonephritis.

• Secondary nephropathy generally refers to diseases affecting the kidneys due to other systemic conditions. Common examples include systemic lupus erythematosus, diabetes, vasculitis, gout-related kidney damage (commonly known as gout), and hypertension, all of which can lead to kidney impairment.

• Interstitial nephritis (tubulointerstitial nephritis) involves damage to renal tubules caused by various factors. It can be acute or chronic, with common causes including infections and medications with nephrotoxic side effects.

• Tubular diseases include renal tubular acidosis and Fanconi syndrome. The former can be further divided into proximal renal tubular acidosis, distal renal tubular acidosis, mixed renal tubular acidosis, and hyperkalemic renal tubular acidosis. These conditions typically result from genetic or toxic factors impairing tubular acidification function.

• Renal vascular diseases include renal artery stenosis, renal artery embolism and thrombosis, arteriolar nephrosclerosis, and renal vein thrombosis. Common clinical manifestations include hypertension, changes in urine, and back pain. Laboratory tests often reveal abnormal urine findings such as hematuria, proteinuria, and elevated creatinine. Imaging studies like ultrasound, CT, and magnetic resonance angiography often provide diagnostic clues.

• Acute kidney injury, previously termed acute renal failure, can be classified into prerenal, intrinsic renal, and postrenal acute kidney injury based on etiology. Common symptoms include signs of toxin and fluid accumulation in the body, such as nausea, vomiting, fatigue, and reduced urine output.

• Chronic kidney failure may present with a wide range of symptoms affecting multiple systems, including:

  • Fluid and electrolyte imbalances, leading to localized or generalized edema, pleural or peritoneal effusions, acidosis, hyperkalemia, and abnormal calcium-phosphorus metabolism.
  • Lipid and protein metabolism disorders, resulting in increased protein breakdown, decreased synthesis, and hyperlipidemia.
  • Cardiovascular symptoms: Renal hypertension, heart failure, pericardial effusion, uremic cardiomyopathy, and atherosclerosis may occur.
  • Respiratory symptoms: Acidosis may cause deep breathing, while uremic pulmonary edema can lead to dyspnea and wheezing.
  • Digestive symptoms: Nausea, vomiting, loss of appetite, and gastrointestinal bleeding may occur.
  • Hematologic symptoms: Primarily renal anemia and reduced platelet function, leading to prolonged bleeding.
  • Neurologic symptoms: Early signs may include fatigue and insomnia, followed by personality changes, depression, and memory impairment. In advanced uremia, seizures, delirium, coma, and hallucinations may develop.
  • Musculoskeletal symptoms: Bone pain, fractures, skeletal deformities, muscle weakness, atrophy, and peripheral sensory abnormalities may occur.
  • Endocrine dysfunction: Possible deficiencies in erythropoietin and 1,25-(OH)2D3, increased renin, glucose metabolism abnormalities, hypothalamic-pituitary hormone imbalances (e.g., prolactin, melanocyte-stimulating hormone, luteinizing hormone, follicle-stimulating hormone, adrenocorticotropic hormone), and peripheral endocrine disorders such as secondary hyperparathyroidism (causing fibrocystic osteitis and fractures), hypothyroidism, and hypogonadism.

CAUSES

What are the common causes of kidney disease?

Kidney diseases can be classified as primary, secondary, or hereditary based on their causes.

• Hereditary diseases: Common examples include polycystic kidney disease, Fanconi syndrome, and Alport syndrome, as well as thin basement membrane nephropathy, Fabry disease, cystinuria, etc. The inheritance patterns vary, including autosomal dominant inheritance (e.g., polycystic kidney disease) and X-linked dominant inheritance (e.g., Alport syndrome).

• Secondary kidney diseases: These refer to kidney damage caused by systemic diseases with clear underlying causes, such as systemic lupus erythematosus, diabetes, hypertension, vasculitis, and myeloma. The focus of treatment for these conditions lies in managing the primary disease to slow the progression of kidney failure.

• Primary kidney diseases have diverse causes, with different diseases having distinct predisposing factors:

  • Glomerular diseases are often related to immune responses. For example, acute glomerulonephritis is primarily associated with an immune reaction triggered by β-hemolytic streptococcal infections, typically occurring 1–3 weeks after conditions like tonsillitis, scarlet fever, or skin infections. Chronic glomerulonephritis is often linked to immune-mediated inflammation.
  • Interstitial nephritis and acute renal failure are frequently associated with nephrotoxic drugs and toxins, such as certain antibiotics, sulfonamides, anticonvulsants, contrast agents, and endogenous substances (e.g., hemoglobin, myoglobin).
  • Renovascular diseases are generally related to the narrowing of renal arteries or veins, caused by conditions like atherosclerosis, Takayasu arteritis, or renal vein thrombosis. Among these, atherosclerosis is the most common cause of renal artery stenosis in China.
  • Acute renal failure may occur when patients experience insufficient renal blood flow due to massive blood loss, dehydration, shock, or heart failure, or when severe urinary tract obstruction (commonly caused by stones or tumors) occurs. In such cases, the underlying cause must be addressed promptly. Patients with blood loss or dehydration require immediate blood transfusion or fluid replacement to restore blood volume and maintain kidney perfusion, while those with urinary obstruction need prompt relief of the blockage to prevent ongoing kidney damage.

Additionally, the causes of many kidney diseases remain incompletely understood, with only speculative links to infections or immune factors.

DIAGNOSIS

What tests are mainly used to diagnose kidney diseases?

• Urine tests: Since the kidneys are the organs that produce urine, urine tests play a crucial role. Routine urinalysis, 24-hour urine protein, urine bacterial culture, and urine smear for acid-fast bacilli can detect red blood cells, white blood cells, casts, urinary protein, and bacteria in the urine. These tests can provide a preliminary diagnosis of kidney disease.

• Hematological tests: The glomerular filtration rate can be calculated based on serum creatinine levels. Additionally, indicators such as hemoglobin, folic acid, ferritin, and erythropoietin can be measured to determine the presence of anemia and whether it is renal anemia.

• Imaging tests: Ultrasound can preliminarily assess kidney size and detect urinary tract stones. Urography and CT scans can identify urinary tract obstructions. Radionuclide tests are often used to evaluate glomerular function in various chronic kidney diseases.

• Kidney biopsy: A kidney biopsy can clarify renal pathology and is highly significant for diagnosing, classifying, and staging various glomerular diseases.

Currently, MRI is less commonly used in nephrology, primarily for assessing renal ischemia. Radionuclide tests are frequently employed to evaluate glomerular function in chronic kidney diseases.

For patients with secondary kidney diseases, the diagnostic tests for their primary conditions are not discussed in detail here.

TREATMENT

Which department should I visit for kidney disease?

Various primary kidney diseases should be treated in the nephrology department.

If the kidney disease is identified as secondary, patients should visit the corresponding department. For example, patients with systemic lupus erythematosus should receive standardized diagnosis and treatment in the rheumatology and immunology department, while myeloma patients should go to the hematology department.

How should kidney disease be treated?

• For patients with clear causes or triggers, the primary disease should be properly treated, and triggers should be promptly eliminated. Meanwhile, maintaining a healthy lifestyle and a reasonable diet is essential, with specific dietary plans varying based on the condition.

• Most primary glomerular diseases involve immune-related pathophysiological processes. Therefore, treatments such as glucocorticoids and immunosuppressants (e.g., cyclophosphamide) play a significant role in nephrology. Specific treatment plans depend on the pathological type of the disease.

• When kidney disease progresses to the uremic stage, renal replacement therapy becomes the only effective treatment. Options include peritoneal dialysis, hemodialysis, and kidney transplantation. Each has its pros and cons, and patients can choose based on their individual circumstances.

• Additionally, kidney diseases, especially chronic renal failure, often lead to complications in other systems. Early detection and correction of these complications can improve quality of life and slow disease progression.

DIET & LIFESTYLE

What should patients with kidney disease pay attention to in their daily lives?

Patients with kidney disease should pay attention to rest, avoid smoking and drinking, exercise moderately, control their emotions, and carefully manage their underlying diseases.

In terms of diet, they should consume more high-quality animal protein rich in essential amino acids, but the amount of protein intake should be controlled to avoid putting excessive pressure on the remaining nephrons.

PREVENTION

Can Kidney Disease Be Prevented? How to Prevent It?

The human kidneys have strong compensatory functions, but we should still raise awareness of kidney protection, avoid exposure to nephrotoxic substances and medications, maintain a healthy lifestyle, undergo regular check-ups, and seek timely treatment if issues arise.

For patients already diagnosed with kidney disease, controlling underlying conditions such as hypertension and diabetes, as well as promptly treating diseases like glomerulonephritis, is crucial to slowing disease progression and preventing chronic kidney failure.