Renal failure means your kidneys can no longer filter waste and excess fluid from your blood effectively. “Renal” simply means “related to the kidneys,” so renal failure and kidney failure are the same thing. The condition ranges from a sudden, temporary loss of kidney function to a slow, permanent decline that develops over months or years.
What Your Kidneys Normally Do
Your kidneys filter your entire blood supply dozens of times a day, pulling out waste products and extra fluid that leave your body as urine. But filtration is only part of the job. Kidneys also balance minerals like calcium and phosphorus in your blood, activate vitamin D so your bones can use it, and help regulate blood pressure. When kidney function drops significantly, all of these processes are disrupted, which is why kidney failure affects far more than just urination.
Acute vs. Chronic Kidney Failure
There are two fundamentally different types. Acute kidney injury comes on suddenly, often within hours or days, and is potentially reversible. It can be triggered by a severe infection (sepsis), a drop in blood flow to the kidneys, or exposure to substances that are toxic to kidney tissue. The other type, chronic kidney disease, progresses slowly over at least three months and can lead to permanent kidney failure.
The distinction matters because the outlook is very different. With acute injury, recovery depends heavily on how well your kidneys were working before the problem started. Research published in the American Journal of Kidney Diseases found that among people whose kidneys were healthy beforehand, more than half recovered enough function to stop dialysis. For those who already had moderate kidney disease, only 17% recovered. Most recovery happens within the first three months, and after six months on dialysis, only about 6% of people regain enough function to come off it.
Leading Causes
Diabetes and high blood pressure are the two most common causes of chronic kidney disease by a wide margin. About 1 in 3 people with diabetes and 1 in 5 people with high blood pressure develop some degree of kidney disease. Both conditions damage the tiny blood vessels inside the kidneys that do the actual filtering work. Over years, that damage accumulates until the kidneys can no longer keep up.
Other causes include autoimmune diseases like lupus, inherited conditions like polycystic kidney disease, repeated kidney infections, and prolonged obstruction of the urinary tract. For acute kidney injury, the triggers tend to be more immediate: major surgery, serious infections, severe dehydration, or medications that are hard on the kidneys.
How Kidney Failure Is Staged
Doctors measure kidney function using a blood test that estimates how efficiently your kidneys filter waste. The result is called your estimated glomerular filtration rate, or eGFR, measured in milliliters per minute. A normal eGFR is above 90. The five stages of chronic kidney disease break down like this:
- Stage 1: eGFR above 90, but other tests show signs of kidney damage
- Stage 2: eGFR of 60 to 89, with signs of damage
- Stage 3a: eGFR of 45 to 59
- Stage 3b: eGFR of 30 to 44
- Stage 4: eGFR of 15 to 29
- Stage 5: eGFR below 15, meaning the kidneys have lost almost all function
Stages 1 and 2 rarely cause noticeable symptoms. Most people don’t feel anything wrong until stage 3 or later, which is why kidney disease is often caught through routine blood work rather than because someone felt sick.
Symptoms to Recognize
Early kidney disease is typically silent. Symptoms tend to appear once function has declined significantly, and they can be easy to mistake for other problems. Common signs include persistent fatigue, nausea, swelling in the hands, ankles, or face, peeing less than usual, dry or itchy skin, muscle cramps, confusion or difficulty concentrating, and a metallic taste that makes food unappealing.
Swelling happens because your kidneys can’t remove enough fluid. Fatigue and confusion set in because waste products build up in your blood. The itchiness comes from mineral imbalances that healthy kidneys would normally correct. None of these symptoms on their own confirms kidney failure, but several of them together, especially reduced urination combined with swelling, should prompt a blood test to check kidney function.
What Happens to the Rest of Your Body
Because kidneys do so much more than make urine, their failure creates a ripple effect across other systems. One of the most significant complications involves your bones. Healthy kidneys convert vitamin D into a form your body can actually use and keep calcium and phosphorus levels balanced. When they stop doing this, your body compensates by pulling calcium out of your bones, weakening them over time. Excess phosphorus that the kidneys can no longer remove can harden blood vessels, raising the risk of heart problems.
The parathyroid glands, small glands in your neck that regulate calcium, go into overdrive trying to compensate. They flood your blood with extra hormone to move calcium from bones into the bloodstream, which restores blood calcium levels but starves the bones. This cycle of mineral imbalance, bone loss, and blood vessel calcification is a major reason why advanced kidney disease carries such a high risk of fractures and cardiovascular disease.
Treatment: Dialysis and Transplant
When kidneys fail completely (stage 5), the two main options are dialysis or a kidney transplant. Dialysis takes over the kidney’s filtering job mechanically, removing waste and excess fluid from your blood.
The most common form is in-center hemodialysis: you go to a clinic three times a week for about four hours each session. Staff handle most of the work, but the time commitment is significant. Home hemodialysis offers more scheduling flexibility, though you and a partner need to complete training and handle equipment setup and monitoring yourselves.
Peritoneal dialysis uses the lining of your abdomen as a natural filter instead of a machine. One version requires you to do four to six fluid exchanges throughout the day, every day. An automated version runs overnight while you sleep, using a machine called a cycler, with one additional exchange in the morning. Peritoneal dialysis gives more independence from a clinic but demands daily consistency.
Kidney transplant is generally the preferred long-term solution when it’s an option. About 36% of people placed on the transplant waitlist receive a kidney within one year, and by three years, just over half have been transplanted. Wait times vary enormously by age: children and adolescents typically receive a transplant within about 16 months, while adults aged 18 to 44 wait a median of nearly five years. For people over 65, fewer than half receive a transplant within five years of being listed.
Dietary Changes
What you eat plays a real role in managing kidney failure. The kidneys normally handle excess sodium, potassium, phosphorus, and the byproducts of protein digestion. When they can’t, those substances build up and cause problems. Federal dietary guidelines recommend no more than 2,300 milligrams of sodium per day for adults, but many people with kidney disease need to go lower than that.
There’s no single kidney diet that works for everyone. The right balance of protein, potassium, and phosphorus depends on your stage of kidney disease, whether you’re on dialysis, and what other conditions you have. Too much protein generates waste your kidneys struggle to clear, but too little leads to muscle loss, especially on dialysis. A dietitian who specializes in kidney disease can tailor recommendations to your specific numbers and situation.