Kidneys fail when something damages their filtering units badly enough that they can no longer clean waste from your blood. The two most common causes are diabetes and high blood pressure, which together account for the majority of chronic kidney disease cases in the United States. But kidneys can also fail suddenly from infections, blockages, or toxic medications. About 1 in 7 U.S. adults, roughly 35.5 million people, already have some degree of chronic kidney disease.
How Healthy Kidneys Work
Each kidney contains roughly one million tiny filtering units called nephrons. Blood flows into each nephron at high pressure, passing through a cluster of microscopic blood vessels that act as a sieve. Waste products and excess fluid get pushed through this sieve into a tube where urine forms, while useful proteins and blood cells stay behind in the bloodstream. Your kidneys process about 50 gallons of blood per day, producing one to two quarts of urine.
When these filters get damaged, they start leaking protein into the urine and lose their ability to remove waste. If enough nephrons are destroyed, the kidneys can no longer keep up, and toxins build in the blood. This is kidney failure.
Diabetes: The Leading Cause
About 1 in 3 people with diabetes develop kidney disease. Persistently high blood sugar damages the delicate cells that line the kidney’s filtering units. The cells most vulnerable are called podocytes, specialized cells that wrap around the blood vessels in each filter and control what passes through.
When blood sugar stays elevated, podocytes begin to change shape and die off. They lose the proteins that hold them in place, causing gaps in the filter. Those gaps allow protein to leak from the blood into the urine, one of the earliest measurable signs of kidney damage. Over time, this process triggers scarring. Scar tissue replaces healthy kidney tissue, and since the body cannot regenerate podocytes, the damage compounds. Years of poorly controlled blood sugar can progressively shut down enough nephrons to cause kidney failure.
High Blood Pressure and Blood Vessel Damage
About 1 in 5 people with high blood pressure develop kidney disease. The mechanism is more straightforward than diabetes: excess pressure physically damages the small blood vessels inside the kidneys. When those vessels stiffen or narrow, less blood reaches the nephrons, and the filtering units slowly starve for oxygen. The kidneys respond by signaling the body to raise blood pressure further, creating a destructive cycle where kidney damage worsens hypertension and hypertension worsens kidney damage.
This progression is typically slow, unfolding over years or decades. Many people with hypertension-related kidney damage have no symptoms until the disease is well advanced.
Medications That Harm the Kidneys
Some of the most commonly used pain relievers can damage kidneys, especially with long-term use. Non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen (Advil, Motrin), naproxen (Aleve), and high-dose aspirin (above 325 mg per day) reduce blood flow to the kidneys. At higher doses or with prolonged use, this reduced flow can cause acute kidney injury or accelerate existing kidney disease.
Prescription corticosteroids like prednisone and dexamethasone stress the kidneys indirectly by causing fluid retention, raising blood pressure, and increasing blood sugar. If you already have reduced kidney function, even topical NSAID gels can contribute to further decline. The risk is highest for people whose kidney filtration rate has already dropped below 60, roughly the threshold where kidneys are working at less than two-thirds capacity.
Sudden Kidney Failure From Sepsis or Dehydration
Kidney failure isn’t always a slow process. Acute kidney injury can develop within hours or days, most commonly in people who are critically ill. Sepsis, the body’s overwhelming response to infection, is the single most common trigger for acute kidney failure in hospital settings. During sepsis, blood pressure drops and inflammatory signals flood the body, cutting off oxygen to kidney cells. The filtering tubes inside the kidneys can die from this oxygen starvation, a condition called acute tubular necrosis.
Severe dehydration, major surgery, and heart failure can cause similar damage by drastically reducing blood flow to the kidneys. Unlike chronic kidney disease, acute kidney injury is sometimes reversible if the underlying cause is treated quickly. But severe or repeated episodes of acute injury can leave permanent scarring that leads to chronic kidney disease down the road.
Physical Blockages in the Urinary Tract
When urine can’t drain properly, pressure backs up into the kidneys and begins destroying tissue. The most common cause of this obstruction is an enlarged prostate in men, followed by kidney stones in middle-aged adults and pelvic masses in women.
The damage starts fast. Within two hours of a complete blockage, rising pressure inside the kidney reduces its ability to filter blood and begins triggering inflammation, tissue death, and scarring. The kidney also loses its ability to concentrate urine or balance electrolytes properly. If the obstruction isn’t relieved, progressive scarring can lead to permanent kidney failure over days to months. This type of kidney damage is often reversible if caught early, which is why sudden difficulty urinating or severe flank pain warrants prompt attention.
Autoimmune and Genetic Conditions
Lupus is one of the most significant autoimmune causes of kidney failure. In lupus, the immune system produces antibodies that attack the body’s own tissues, including the kidneys. These antibodies bind to cells inside the kidney’s filters, triggering inflammation and activating a cascade of scarring. If the inflammation persists, normal kidney tissue gets replaced by dense scar tissue in a process called glomerulosclerosis. Without treatment, lupus nephritis can progress to end-stage kidney failure.
Polycystic kidney disease, the most common genetic cause, produces fluid-filled cysts that grow inside the kidneys over decades. As the cysts enlarge, they compress and destroy surrounding healthy tissue. Other inherited conditions affect the kidney’s structure or its ability to handle certain proteins, but polycystic kidney disease is by far the most prevalent.
How Kidney Function Is Measured
Doctors track kidney health using a blood test that estimates how well your kidneys filter, expressed as a number called eGFR (estimated glomerular filtration rate). A normal eGFR is 90 or above. The stages of kidney disease break down like this:
- Stage 1 (eGFR 90+): Normal filtration rate, but other signs of kidney damage like protein in the urine are present.
- Stage 2 (eGFR 60-89): Mildly decreased function. Usually no symptoms.
- Stage 3 (eGFR 30-59): Moderate loss of function. Waste products may start building up in the blood.
- Stage 4 (eGFR 15-29): Severe loss. Symptoms become more noticeable, and planning for dialysis or transplant often begins.
- Stage 5 (eGFR below 15): Kidney failure. The kidneys can no longer sustain life without dialysis or a transplant.
The tricky part is that stages 1 through 3 rarely produce obvious symptoms. Most people feel fine until they’ve lost more than half their kidney function.
Warning Signs to Recognize
Early kidney disease is sometimes called a “silent” condition because it produces no pain and few noticeable changes. The first detectable sign is often protein leaking into the urine, which shows up on a routine lab test before you notice anything wrong. Protein in the urine also signals increased risk of heart disease, so doctors screen for it regularly in people with diabetes.
As kidney function declines further, waste products accumulate in the blood. This can cause fluid retention (swelling in the ankles, feet, or hands), persistent fatigue, nausea, and vomiting. Changes in urination are also common: cloudy or reddish urine, a frequent urge to urinate, or pain during urination. Pain in the back or side below the ribs can signal a kidney infection or stones rather than chronic kidney disease, but either way it points to a kidney problem worth investigating.
Because the early stages are silent, the people at highest risk (those with diabetes, high blood pressure, or a family history of kidney disease) benefit most from regular blood and urine testing. Kidney damage caught at stage 1 or 2 can often be slowed or stabilized. By stage 4 or 5, the options narrow considerably.