Renal impairment, also known as kidney disease, occurs when the kidneys lose their ability to filter waste and excess fluid from the blood effectively. This condition can develop gradually over time or appear suddenly, affecting millions of people worldwide and leading to serious health complications if left unmanaged.
Understanding Renal Impairment
Renal impairment describes a condition where the kidneys cannot perform their essential functions as well as they should. Your kidneys are bean-shaped organs, each about the size of your fist, located under your ribcage toward your back. Their primary job is to clean your blood by filtering out toxins, waste products, and excess water, which then leave your body as urine. When the kidneys are damaged and cannot filter blood properly, waste and fluid begin to build up in your body, potentially causing serious health problems.[1]
The term renal impairment can describe different patterns of kidney problems. Sometimes kidney function declines quickly over hours or days, a situation called acute kidney injury. In other cases, damage develops slowly over months or years, leading to chronic kidney disease. Chronic kidney disease represents a long-term condition where kidney damage cannot be reversed, though its progression can often be slowed with proper treatment.[3]
Renal impairment is classified into stages based on how well the kidneys filter substances. Healthcare providers use a measurement called the estimated glomerular filtration rate, or eGFR, which is calculated from a blood test. A normal eGFR is above 90, while the lowest is 0, meaning no remaining kidney function. The five stages range from mild damage with near-normal function in Stage 1, to kidney failure in Stage 5, where the eGFR drops below 15.[1]
How Common Is Renal Impairment?
Renal impairment affects a substantial portion of the population. In the United States alone, more than 35.5 million adults are estimated to have chronic kidney disease, and most remain undiagnosed. The condition affects over 750,000 people each year when considering all forms of kidney failure, and approximately 2 million people worldwide live with end-stage kidney disease requiring dialysis or transplantation.[1][8]
One of the most concerning statistics is that more than one in seven American adults has chronic kidney disease, yet as many as nine in ten do not know they have it. This means that approximately 90 percent of people with the condition remain unaware until it progresses to more advanced stages. Additionally, about 40 percent of people with severely reduced kidney function who are not yet on dialysis are unaware of having the disease.[8]
Chronic kidney disease is more common in certain populations. It affects people who are Black or of South Asian origin at higher rates than others. The condition also becomes more prevalent as people age, making it particularly common among older adults.[7]
What Causes Renal Impairment?
The causes of renal impairment vary depending on whether the condition develops suddenly or gradually. For chronic kidney disease, which develops slowly over time, the condition is usually caused by other health problems that put strain on the kidneys. Often, it results from a combination of different underlying issues working together to damage kidney tissue.[7]
Diabetes and high blood pressure are the two most common causes of chronic kidney disease and kidney failure. Unmanaged diabetes leads to high blood sugar levels that can damage the small blood vessels in the kidneys. Over time, this damage prevents the kidneys from filtering blood effectively. Similarly, high blood pressure over extended periods puts strain on the small blood vessels in the kidneys, eventually causing them to stop working properly. In fact, approximately one in three adults with diabetes and one in five adults with high blood pressure may develop chronic kidney disease.[1][8]
High cholesterol can cause fatty deposits to build up in the blood vessels that supply the kidneys, making it harder for these organs to work properly. Repeated kidney infections can also lead to permanent damage. A condition called glomerulonephritis, which involves inflammation of the kidney’s filtering units, is another cause of kidney damage.[7]
Some people develop kidney disease due to inherited conditions. Autosomal dominant polycystic kidney disease is an inherited condition where fluid-filled growths called cysts develop in the kidneys, gradually destroying healthy tissue. Blockages in urine flow, such as from recurring kidney stones or an enlarged prostate, can also damage the kidneys over time.[7]
Long-term, regular use of certain medications can harm the kidneys as well. These include lithium, used for mental health conditions, and non-steroidal anti-inflammatory drugs (NSAIDs), commonly used pain relievers like ibuprofen. When used frequently over long periods, these substances can impair kidney function.[7]
Risk Factors for Developing Renal Impairment
Several factors increase the likelihood of developing renal impairment. Some of these factors cannot be changed, while others can be managed through lifestyle adjustments and medical care. Understanding your personal risk can help you take steps to protect your kidney health.
Having diabetes is one of the strongest risk factors for kidney disease. When blood sugar levels remain high over time, they damage the delicate filtering structures inside the kidneys. Similarly, having high blood pressure significantly increases your risk because the constant pressure damages the blood vessels in the kidneys, reducing their ability to function.[8]
A family history of kidney failure puts you at higher risk of developing kidney disease yourself. If a parent or sibling has had kidney failure, your chances of developing the condition increase. Heart disease is another important risk factor, as the kidneys and heart are closely connected in maintaining overall cardiovascular health.[8]
When renal impairment is caused by problems with blood flow to the kidneys, additional risk factors come into play. These are similar to risk factors for atherosclerosis, the buildup of fatty deposits in arteries. They include older age, gender, race or ethnicity, genetic factors, elevated fats in the blood (hyperlipidemia), smoking, and obesity. People who have been diagnosed with coronary artery disease or peripheral artery disease face greater risk for developing reduced blood flow to the kidneys.[9][16]
Recognizing the Symptoms of Renal Impairment
In the early stages of chronic kidney disease, most people experience few or no symptoms. The condition may only be discovered through routine blood or urine tests performed for another reason. This silent progression makes kidney disease particularly dangerous, as significant damage can occur before a person realizes anything is wrong.[7]
When symptoms do appear, they typically indicate that kidney disease has progressed to more advanced stages. If your kidneys are not working properly, you may notice extreme tiredness or fatigue that does not improve with rest. This happens because damaged kidneys cannot produce enough of a hormone that signals the body to make red blood cells, leading to anemia.[1]
Nausea and vomiting are common symptoms as waste products build up in the blood. You might also experience confusion or trouble concentrating, sometimes described as brain fog. This occurs because toxins that would normally be filtered out by healthy kidneys remain in your bloodstream and affect brain function.[1]
Swelling, medically called edema, often appears around the hands, ankles, or feet. This happens because damaged kidneys cannot remove excess fluid from the body effectively. You may notice changes in how often you urinate, including waking up at night to pass urine, or seeing blood in your urine.[1][3]
Other symptoms include muscle cramps, dry or itchy skin, poor appetite, and food tasting metallic. Shortness of breath may develop as fluid builds up in the lungs, and restless legs can interfere with sleep. As kidney failure develops further, you may experience worsening swelling, including fluid accumulation in the lungs and abdomen, along with increasing confusion and problems with memory.[1][3]
For acute kidney injury, which develops rapidly, the first symptom is usually a decreased amount of urine. Early symptoms may include swelling, weight gain, and changes in blood test results. Late symptoms can include tiredness, trouble concentrating, confusion, changes in breathing, and seizures. Once recovery begins, you will start producing a lot of urine before returning to normal levels.[3]
Preventing Renal Impairment
While some risk factors for kidney disease cannot be changed, many preventive measures can protect your kidneys and reduce your risk of developing renal impairment. Taking action early, especially if you have risk factors like diabetes or high blood pressure, can make a significant difference in maintaining kidney health.
Keeping your blood pressure under control is vital to protect your kidneys. Healthcare providers generally recommend keeping blood pressure below 140/90 mm Hg, though if you have diabetes, the target is usually lower, below 130/80 mm Hg. Several types of blood pressure medications exist, but medicines called angiotensin converting enzyme (ACE) inhibitors and angiotensin-II receptor blockers (ARBs) are particularly effective because they not only lower blood pressure but also provide additional kidney protection.[7][8]
If you have diabetes, staying within your target blood sugar range as much as possible is crucial. Good control of blood sugar levels helps prevent damage to the small blood vessels in your kidneys. Healthcare providers recommend aiming for a hemoglobin A1c level below 7 percent.[8]
Eating a healthy, balanced diet benefits your kidneys and overall health. Your diet should include plenty of fresh fruits and vegetables, aiming for at least five portions daily. Include meals with starchy foods like potatoes, whole grain bread, rice, or pasta. Choose lean proteins such as fish, poultry, eggs, beans, or pulses. Limit saturated fats, salt, and added sugars. Reducing salt intake to less than 2,300 milligrams per day, roughly one teaspoon, helps protect your kidneys and control blood pressure.[7][8]
Regular physical activity strengthens your entire body, including your cardiovascular system, which supports kidney health. Aim for at least 150 minutes of moderate exercise each week. Exercise boosts energy, helps you sleep, strengthens bones, wards off depression, and may reduce your risk of heart disease, which is closely linked to kidney health.[7][8]
If you smoke, stopping is one of the best things you can do for your kidneys. Smoking worsens kidney disease and interferes with blood pressure medications. Managing your alcohol intake is also important; limit consumption to no more than 14 units per week. Losing weight if you are overweight or obese reduces strain on your kidneys and helps control blood pressure and blood sugar.[7][8]
Avoid over-the-counter non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen unless advised by a medical professional, as these can harm your kidneys, especially if you already have kidney disease. Check with your doctor or pharmacist before taking any over-the-counter medicines or nutritional supplements, as some can affect kidney function or interfere with prescribed medications.[7]
If you are at high risk for kidney disease due to diabetes, high blood pressure, or family history, regular testing is essential. Early detection through routine blood and urine tests allows for earlier intervention, which can slow or prevent progression of kidney damage. Getting annual flu shots and the pneumococcal vaccination is also recommended, as kidney disease can weaken your immune system and make you more vulnerable to infections.[8]
How Renal Impairment Affects Your Body
Understanding what happens inside your body when your kidneys are not working properly helps explain why the symptoms occur and why treatment is so important. The kidneys perform several critical jobs beyond filtering waste, and when they fail, multiple body systems are affected.
Healthy kidneys filter all the blood in your body approximately every 30 minutes. They remove wastes, toxins, and excess fluid, sending these out of your body as urine. They also help control blood pressure, signal the body to make red blood cells, keep bones healthy, and regulate blood chemicals that are essential to life.[8]
When the kidneys are damaged and cannot filter blood as well as they should, waste products and excess fluid remain in the body instead of being removed. This buildup of waste in the blood causes many of the symptoms associated with kidney disease. Toxins accumulating in the bloodstream can affect brain function, leading to confusion and difficulty concentrating. They also cause nausea, vomiting, and poor appetite.[8]
Because damaged kidneys cannot remove excess fluid effectively, water accumulates in tissues throughout the body, causing swelling in the hands, ankles, and feet. Fluid can also build up in the lungs, leading to shortness of breath. The inability to properly balance electrolytes like potassium and sodium can cause dangerous changes in heart rhythm, muscle weakness, and other serious complications.[8]
Renal impairment affects red blood cell production because the kidneys normally produce a hormone called erythropoietin, which signals the body to make these cells. When kidney function declines, less of this hormone is produced, leading to anemia. This explains the extreme fatigue and weakness that many people with kidney disease experience.[8]
The kidneys also play a crucial role in bone health by activating vitamin D, which helps the body absorb calcium. When kidney function is impaired, this process is disrupted, potentially leading to weak bones and an increased risk of fractures. Additionally, imbalances in calcium and phosphorus levels can cause the parathyroid glands to become overactive, a condition called secondary hyperparathyroidism.[8]
Chronic kidney disease significantly increases the risk of cardiovascular problems, including heart disease and stroke. This happens partly because some causes of kidney disease, like high blood pressure and high cholesterol, are also risk factors for heart disease. The buildup of waste products in the blood and changes in fluid balance also put additional strain on the heart.[8]
For renal impairment caused by reduced blood flow to the kidneys due to narrowed arteries (renal artery stenosis), the lack of adequate blood supply prevents the kidneys from functioning properly. This condition may cause no symptoms in some patients, while others develop dangerously high blood pressure or progress to kidney failure requiring dialysis.[9][16]
