What Is Kidney Disease?

Kidney disease refers to any condition that damages the kidneys, the two bean-shaped organs located on each side of the spine that filter blood, produce urine, and regulate fluid and acid levels in the body. Kidney disease can be acute, meaning fast developing and severe, or chronic, meaning persistent and progressive.

Acute kidney injury (AKI) is a form of kidney disease that can be serious but is usually reversible. Chronic kidney disease (CKD) is typically nonreversible and often asymptomatic (without symptoms) for years until the kidneys start to fail and eventually stop working altogether.

This article describes the differences between acute and chronic kidney diseases, including their causes and how they are diagnosed. It also takes an in-depth look at CKD, including how it progresses and is treated at different stages.

Types and Causes of Kidney Disease: Acute vs. Chronic

With acute kidney injury, kidney damage occurs suddenly but can usually be reversed once the underlying cause is treated. With chronic kidney disease, the damage develops gradually and is most often incurable.

The underlying causes tend to be distinct and affect the kidneys differently.

Acute Kidney Injury

Acute kidney injury, formerly called acute renal failure, is a sudden decrease in kidney function that occurs within seven days. The injury can be prerenal (due to decreased blood flow to the kidneys), intrarenal (due to damage to the kidneys themselves), or postrenal (due to blockage of urine flow from the kidneys).

Some of the most common of AKI include:

Chronic Kidney Disease

Chronic kidney disease is the gradual loss of kidney function over months or years. CKD is characterized by changes to structures of the kidneys—including blood vessels and filtering units called nephrons—that tend to get worse over time.

In the United States, the following two diseases account for more than two-thirds of CKD diagnoses:

• Diabetes: High blood sugar from diabetes can damage blood vessels servicing the kidneys, causing progressive damage as the blood supply decreases. It can also directly damage nephrons and the tiny capillaries inside nephrons (called glomeruli) that filter blood.
• High blood pressure (hypertension): High blood pressure causes the walls of blood vessels to harden and narrow, depriving the kidneys of the blood, oxygen, and nutrients they need to function and survive.

Other causes of CKD include glomerulonephritis, (a group of diseases that cause inflammatory damage to glomeruli) and polycystic kidney disease (an inherited disorder that causes fluid-filled cysts in or on the kidneys).

Kidney Disease Symptoms: Can You Tell Which Type You Have by the Signs?

One of the main differences between AKI and CKD is the timing and severity of symptoms. With AKI, the symptoms will develop rapidly and are usually pronounced. With CKD, the disease is often asymptomatic and, even when signs appear, they are frequently non-specific and easily mistaken for other conditions.

Common signs and symptoms of AKI and CKD include:

As CKD edges closer to kidney failure, the symptoms will start to echo those of AKI and be harder to miss.

When to See a Healthcare Provider for Kidney Problems

You should see a healthcare provider if you have any signs of kidney disease but may need to do so urgently if the symptoms develop suddenly and severely.

Call 911 or go to your nearest emergency room if you develop the following signs and symptoms of acute kidney injury:

• Severe shortness of breath
• Blood in your urine
• Nausea and vomiting
• Inability to urinate
• Severe flank pain
• Changes in consciousness or alertness
• Seizures
  

CKD Symptom Progression and Stages

Chronic kidney disease progresses in five distinct stages. The stages are based on how well your kidneys function as measured by a test known as the estimated glomerular filtration rate (eGFR).

As the eGFR declines from normal values of 90 and over, the risk and severity of symptoms increase. When the eGFR drops below 15, the kidneys are no longer functional, and the condition is known as end-stage renal disease (ESRD).

Complications of Chronic Kidney Disease

As CKD progresses and the kidneys start to fail, other organ systems can become affected and require medical treatment.

The seven most common complications of CKD include:

• High blood pressure: In the same way that high blood pressure can cause CKD, CKD can cause high blood pressure by making it harder for the heart to pump blood to the major arteries of the kidneys.
• Coronary artery disease: In tandem with hypertension, CKD can give rise to atherosclerosis (hardening of the arteries) and coronary artery disease (CAD), both of which contribute to an increased risk of heart attacks and heart failure.
• Mineral and bone disease: The inability to maintain the normal balance of calcium and phosphorus can cause numerous health problems, including bone pain, brittle bones, heart and nerve dysfunction, blocked blood vessels, and delayed growth in children.
• Chronic anemia: When CKD damages kidneys, they produce less of a hormone called erythropoietin (EPO) that stimulates the production of red blood cells in the bone marrow. This leads to a type of anemia known as anemia of chronic disease.
• Edema: The inability of the kidneys to balance sodium and water can lead to the swelling of tissues, known as edema. The overload of fluid, in turn, contributes to high blood pressure.
• Metabolic acidosis: The inability of the kidneys to filter acids can lead to the buildup of acids, known as metabolic acidosis. This causes bone and lean muscle loss and speeds the progression of CKD.

Who Is at Risk of Kidney Disease?

Some people are at greater risk of kidney disease than others. Although there is some overlap in the risk factors of AKI and CKD, they tend to develop independently of each other. With AKI, the injury is usually the result of an acute episode of a chronic or severe illness, while CKD is usually the result of progressive damage from a chronic illness.

CKD is diagnosed more often in people who are Black, Latinx, Asian, or Native American than in White people in the United States.

Kidney Disease Testing: How to Diagnose Kidney Disease

Kidney disease is diagnosed with blood and urine tests. The tests evaluate the function of the kidneys in different ways and are collectively referred to as renal function tests.

The tests include:

• Serum creatinine: This blood test measures a waste byproduct called creatinine, which is produced steadily as muscles are broken down. High creatinine levels mean the kidneys are clearing the byproduct as they should.
• Estimated glomerular filtration rate (eGFR): This blood test calculates how well the kidneys are working based on your serum creatinine levels and the expected values for your age, body size, and biological sex.
• Urine albumin-to-creatinine ratio (UACR): This urine test can detect albuminuria, a condition in which damaged kidneys release too much protein (called albumin) into your urine. Kidney function is measured by comparing albumin levels with creatinine levels.

The underlying cause of kidney disease can be diagnosed with imaging tests (such as an abdominal ultrasound) or by obtaining a sample of kidney tissue with a biopsy.

Chronic Kidney Disease Treatment 

The treatment of CKD varies by the stage of the disease, the underlying causes, and other factors.

Lifestyle

Lifestyle changes are recommended at every stage of CKD to keep you healthy and slow the progression of the disease.

These include:

• Limiting salt intake: People with CKD and hypertension should consume no more than 2,400 milligrams (mg) of sodium from all sources daily.
• Limiting protein intake: Talk to your healthcare provider about the appropriate amount of protein for your stage of CKD and how to balance your diet.
• Quitting cigarettes: Cigarette smoking causes the narrowing of arteries and veins, further restricting blood flow to the kidneys. Smokers with diabetes also have a harder time controlling their blood sugar, even with insulin injections.
• Maintaining a healthy weight: This includes eating a balanced diet and exercising at least 150 minutes weekly. Shedding excess pounds helps lower blood pressure and blood sugar.

Medications

Different medications may be prescribed to manage the underlying causes and complications of CKD, including:

• ACE (angiotensin-converting enzyme) inhibitors like Altace (ramipril) and Vasotec (enalapril) that reduce blood pressure
• Antidiabetic drugs like Farxiga (dapagliflozin) that reduce blood sugar
• Loop diuretics like Lasix (furosemide) that treat fluid overload
• Statin drugs like Lipitor (atorvastatin) and Zocor (simvastatin) that lower cholesterol
• Potassium binders like Lokelma (sodium zirconium cyclosilicate) that treat high potassium
• Iron supplements or erythropoietin infections that treat anemia
• Calcium supplements that replace lost calcium and protect bones

Dialysis

For the small proportion of people who progress to ESRD, dialysis may be needed to remove waste from your body when the kidneys can no longer do so.

There are two types commonly used:

• Hemodialysis involves a machine that removes wastes and fluids from your blood. It is performed in a center three times weekly, with each treatment lasting four hours. There are also home units you can connect yourself to four to five times weekly.
• Peritoneal dialysis is a procedure performed at home using the lining of the abdomen as a filter. Fluids are manually pumped into and suctioned out of the abdomen several times a day to remove waste. Newer continuous cycling machines allow you to do so while you are asleep.

Kidney Transplant

A kidney transplant is another treatment option for ESRD. Typically, when a person with CKD has an eGFR of 20, they are assessed to determine if they are a candidate for a transplant and placed on a waiting list.

The kidney may come from a deceased or living donor. The donor is "matched" so that their blood and tissue types are compatible, minimizing the risk of organ rejection.

A transplant can be performed without dialysis if the kidney failure is progressing slowly and the symptoms can be controlled with diet and medications. If not, a person may be placed on dialysis until a donor kidney is received.

Daily CKD Management

Managing CKD requires a commitment to good health. In addition to making lifestyle changes, the National Institutes of Health recommend that you aim for the following goals in your daily life:

• Control your blood pressure: The blood pressure goal is less than 140/90 millimeters of mercury (mm Hg) for most people. If you cannot do so with diet and exercise, speak with your healthcare provider about ACE inhibitors and other drugs that can help.
• Meet your blood sugar goals: You must regularly check your blood glucose (sugar) levels and A1C (the average blood glucose levels over the past three months). The A1C goal for many people with diabetes is under 7%.
• Build a sustainable diet: Building a healthy, balanced diet when foods are restricted is important. To better meet your daily nutritional needs, ask your healthcare provider for a referral to a dietitian certified in managing CKD.
  
• Manage your stress: Depression is common among people with CKD and can make the disease harder to manage. If you have trouble coping, speak with a mental health professional, connect with a support group, or reach out to friends or family members. Avoid drugs and alcohol, and try to get at least seven to eight hours of sleep per night.

It is also important to stay in touch with your care team. Your kidney specialist (nephrologist) monitors your lab results and adjusts treatment if there are changes in your kidney function. Let your nephrologist and care team know about any changes in your health or treatment, including those unrelated to your kidneys.

Outlook

The prognosis (outlook) of acute kidney injury is generally good if treated appropriately. In some cases, AKI may be a one-off event without impacting your long-term health or life expectancy.

The prognosis of chronic kidney disease can vary by the individual. With that said, most people with CKD do not progress to ESRD because symptoms tend to develop in later life and can usually be managed with medications and diet. The most common cause of death in people with CKD is heart disease rather than kidney failure.

The risk of death is largely influenced by the stage of CKD. According to a 2017 study in Pediatric Nephrology, a 30-year-old male with an eGFR of 60 and over can expect to live to 79, while a counterpart with an eGFR under 15 may only live to 45.

Prognosis for End-Stage Renal Failure

For those who progress to ESRD, dialysis and kidney transplantation are the only options for survival. If neither is pursued, death usually occurs within several days or weeks.

Those pursuing dialysis have a far better outlook, with an average life expectancy of five to 10 years.

Success rates for kidney transplants are equally optimistic, with 78.2% of those who received a kidney from a deceased donor living for at least five years. Around 88.1% of those who received a kidney from a living donor surviving for a least five years.

Even recipients in their 60s can expect to live anywhere from 11 to 15 years after a transplant.