What is chronic kidney disease?

Chronic kidney disease (CKD) is a long-term condition characterized by the gradual loss of kidney function over time. The kidneys, vital for filtering waste and excess fluids from the blood, play a critical role in maintaining the body’s balance. When kidney function diminishes, waste products and fluids build up in the body, leading to a wide array of health problems. CKD is classified into five stages based on the estimated glomerular filtration rate (eGFR), which measures how well the kidneys are functioning. Early stages may be asymptomatic, but symptoms become prominent as the disease progresses, particularly in stages 4 and 5.

The symptoms of CKD vary and often develop slowly, becoming more noticeable as kidney function worsens. Fatigue and weakness are common due to a buildup of toxins in the blood. Many individuals also experience changes in urination, such as increased or decreased frequency, or even the presence of foamy or discolored urine. Swelling in the legs, ankles, and face (edema) can occur due to fluid retention. In advanced stages, shortness of breath, high blood pressure, nausea, vomiting, and loss of appetite may be more pronounced, severely affecting daily life. A comprehensive list of symptoms include the following:

• Fatigue and weakness: Due to toxin buildup in the blood.
• Changes in urination: Includes increased or decreased urination, especially at night (nocturia), and foamy or dark-colored urine.
• Swelling (edema): Fluid retention in the legs, ankles, feet, or face.
• Shortness of breath: Caused by fluid retention in the lungs.
• High blood pressure (hypertension): Worsens over time due to kidney damage.
• Nausea and vomiting: Caused by the buildup of waste products in the blood (uremia).
• Loss of appetite and unintended weight loss.
• Itching (pruritus): Often due to toxin accumulation.
• Muscle cramps: Caused by electrolyte imbalances.
• Metallic taste in the mouth and bad breath (uremic odor).
• Difficulty concentrating or mental confusion.
• Chest pain: Resulting from fluid overload or inflammation around the heart (pericarditis).

Diagnosis of CKD involves several tests and evaluations which may reveal a problem even before any symptoms arise. The process usually starts with a medical history and physical examination, in which doctors assess risk factors such as diabetes or high blood pressure, common causes of CKD, as well as family history. Blood tests to measure serum creatinine and calculate the eGFR are essential for estimating kidney function. Urine tests detect abnormalities such as protein or blood, and are used to calculate the albumin-to-creatinine ratio (ACR). Imaging studies like ultrasound or CT scans can provide insight into kidney structure. In some cases, a kidney biopsy may be performed to assess the degree of damage and pinpoint the cause of CKD.

eGFR in particular is a crucial test to estimate how well your kidneys are filtering blood, and is used to stage CKD. The eGFR is calculated from a blood test that measures the level of creatinine, a waste product produced by muscle metabolism. The formula to estimate eGFR incorporates several variables, including age, sex, and race. eGFR is typically expressed in milliliters per minute per 1.73 square meters of body surface area (mL/min/1.73 m²) representing kidney filtration function. It can be influenced by factors such as muscle mass, diet, and hydration status.

The ACR is a urine test used to assess the amount of albumin (a protein) relative to creatinine. Elevated ACR values are a key indicator of kidney damage, particularly in the context of diseases like diabetes and hypertension. Both eGFR and ACR are used together to monitor the progression of CKD and to guide treatment decisions.

The prognosis of CKD depends on the stage at which it is diagnosed and how well it is managed. In the early stages (1-3), progression can often be slowed with effective management of underlying conditions such as diabetes and hypertension. However, in the later stages (4-5), kidney function declines significantly, often leading to end-stage renal disease (ESRD), which requires dialysis or a kidney transplant for survival (Figure 1). Complications such as cardiovascular disease, electrolyte imbalances, and anemia also play a role in determining the overall prognosis, as these conditions are common in individuals with advanced CKD.

Chronic kidney disease (CKD) is a relatively common condition globally, affecting approximately 8-16% of the adult population worldwide. People with diabetes and hypertension are particularly vulnerable, as these conditions are leading causes of kidney damage. Older adults, especially those over 60, are also more prone to CKD due to natural age-related declines in kidney function. Additionally, individuals with a family history of kidney disease, cardiovascular disease, or autoimmune disorders like lupus are at increased risk. Certain racial and ethnic minorities, such as African Americans, Hispanics, and Native Americans, also face a higher incidence of CKD due to genetic and socioeconomic factors.

Among risk factors that contribute to the development of CKD, age, diabetes and hypertension are the most significant. Cardiovascular disease also plays a key role, as the heart and kidneys are closely linked in maintaining overall health. Other risk factors include obesity, smoking, and a sedentary lifestyle, all of which can lead to metabolic imbalances that strain the kidneys. A comprehensive list of risk factors include:

• Diabetes and hypertension, which account for the majority of CKD cases.
• Cardiovascular disease, closely linked to kidney health.
• Family history of kidney disease or inherited kidney conditions like polycystic kidney disease (PKD).
• Age, as kidney function naturally declines with age.
• Obesity, which increases the risk of developing diabetes and hypertension.
• Smoking, which damages blood vessels and impairs kidney function.
• Ethnicity, as certain racial groups face a higher risk of CKD.
• Autoimmune diseases, chronic kidney infections, or **urinary tract obstructions** can also increase the risk.

Treatment for CKD focuses on slowing disease progression, managing symptoms, and preventing complications; CKD cannot be reversed. Addressing the underlying cause, such as controlling blood sugar in diabetic patients or lowering blood pressure in hypertensive patients, is essential. Medications like ACE inhibitors and ARBs are commonly prescribed to protect kidney function and manage blood pressure. Lifestyle changes, including a low-sodium diet, regular physical activity, and avoiding smoking, play an important role in maintaining kidney health.

For those in the advanced stages of CKD, managing complications becomes a critical aspect of treatment. Anemia, bone disease, and electrolyte imbalances are common and require specific interventions such as erythropoietin injections, phosphate binders, and vitamin D supplements. In cases of end-stage renal disease (ESRD), dialysis or kidney transplantation is necessary. Dialysis uses a machine to filter waste products and fluids when the kidneys are no longer capable, while transplantation offers the best long-term outcome, though it requires finding a suitable donor and lifelong immunosuppressive therapy to prevent rejection. Early diagnosis and proactive management are key to slowing CKD’s progression and improving quality of life for affected individuals.

In conclusion, chronic kidney disease is a significant public health concern that affects millions of people worldwide. It can lead to severe complications, especially in its later stages, but early detection and proper management of underlying causes such as diabetes and hypertension can significantly improve outcomes. By addressing risk factors, implementing lifestyle changes, and adhering to medical treatments, individuals with CKD can manage their condition and improve their quality of life, even in the face of this chronic, progressive disease.

Figure 1. The five stages of chronic kidney disease.