People need dialysis when their kidneys can no longer filter waste and excess fluid from the blood on their own. Healthy kidneys clean about half a cup of blood every minute, but when they lose 85% or more of that capacity, toxic byproducts build up to dangerous levels. At that point, dialysis takes over the job to keep you alive. Roughly 5 million people worldwide are currently on some form of kidney replacement therapy.
What Healthy Kidneys Actually Do
Your kidneys do far more than make urine. They remove waste products generated by your cells, pull excess water from your blood, and maintain a precise balance of sodium, potassium, calcium, and phosphorus. They also neutralize acid your body produces constantly through normal metabolism. On top of all that, kidneys produce hormones that regulate blood pressure, signal your bone marrow to make red blood cells, and keep your bones strong.
When kidneys start to fail, every one of these functions degrades. Waste accumulates, fluid builds up, minerals swing out of balance, and hormone production drops. The body has no backup system for this work, which is why kidney failure is life-threatening without intervention.
The Main Causes of Kidney Failure
Diabetes and high blood pressure are the two leading causes of chronic kidney disease. Diabetes damages the tiny blood vessels inside the kidneys over years, gradually reducing their filtering power. High blood pressure does something similar, putting constant strain on those same delicate vessels until they scar and stiffen. Together, these two conditions account for the majority of people who eventually need dialysis.
Other paths to kidney failure include autoimmune diseases like lupus, inherited conditions like polycystic kidney disease, recurring kidney infections, and prolonged obstruction of the urinary tract. Acute kidney injury from severe dehydration, major surgery, sepsis, or certain medications can also shut kidneys down suddenly, though in these cases dialysis is often temporary while the kidneys recover.
How the Body Signals Kidney Failure
As waste products pile up in the blood, a condition called uremia develops. Early signs are easy to dismiss: fatigue, poor appetite, nausea, trouble concentrating, and a persistent bad taste in the mouth. You might notice muscle cramps, restless legs, or itchy skin that doesn’t respond to lotion. Swelling in the ankles, feet, or face is common as the kidneys lose the ability to remove extra fluid.
Left untreated, uremia gets worse. Confusion, memory problems, drowsiness, and emotional instability can set in as toxins affect the brain. In severe cases, this progresses to seizures, stupor, or coma. Other late-stage signs include a urine-like odor on the breath, whitish crystals of urea deposited on the skin, bleeding gums, fluid backing up into the lungs, and dangerous spikes in potassium that can cause fatal heart rhythms. At this stage, dialysis becomes an emergency.
When Dialysis Becomes Necessary
Kidney function is measured by how efficiently the kidneys filter blood, expressed as an estimated glomerular filtration rate (eGFR). A healthy eGFR is above 90. Kidney disease is classified in five stages, with stage 5 defined as an eGFR below 15, meaning the kidneys are working at less than 15% capacity. Dialysis is typically needed at or near this threshold, though the exact timing depends on symptoms rather than a single number.
Current clinical guidelines emphasize starting dialysis based on how a person feels and how well their body is managing, not just their lab results. Doctors also use risk prediction tools that estimate the probability of needing treatment within two years. If that risk exceeds 40%, planning for dialysis or a kidney transplant usually begins. For older patients or those with other serious illnesses, the decision may also weigh quality of life, since dialysis is a significant commitment.
How Hemodialysis Works
Hemodialysis routes your blood through a machine containing a filter called a dialyzer. Inside, blood flows on one side of a thin membrane while a special cleaning solution flows on the other side. Waste molecules in the blood naturally move across the membrane toward the cleaner solution, driven by the concentration difference between the two liquids. At the same time, the machine pulls excess fluid out of the blood.
Most people on hemodialysis go to a clinic three times a week for sessions lasting about four hours each. A surgically created connection in the arm, called a fistula, provides reliable access to the bloodstream. Some people do hemodialysis at home, either on the same schedule or more frequently with shorter sessions. Home treatments can offer more flexibility, but they require training and the right setup.
How Peritoneal Dialysis Works
Peritoneal dialysis uses the lining of your abdomen as a natural filter instead of an external machine. A permanent catheter placed in the belly allows you to fill the abdominal cavity with a sterile cleaning solution. The fluid sits there for a few hours while the membrane lining your organs absorbs waste and excess water from the surrounding blood vessels. You then drain the used fluid and replace it with a fresh batch.
There are two main approaches. With the manual method, you perform exchanges yourself about four times a day, each taking around 30 to 90 minutes. With the automated method, a small bedside machine cycles fluid in and out roughly six times over eight hours while you sleep. Peritoneal dialysis happens at home, which appeals to people who want more independence and fewer clinic visits.
Temporary vs. Lifelong Dialysis
Not everyone who starts dialysis stays on it permanently. Acute kidney injury, caused by things like severe infection, a reaction to medication, or major blood loss during surgery, can temporarily shut the kidneys down. In these situations, dialysis supports the body while the kidneys heal, and many patients recover enough function to stop treatment within days or weeks.
Chronic kidney disease is different. The damage accumulates over years and is not reversible. Once someone with chronic kidney disease reaches the point of needing dialysis, the only way off it is a kidney transplant. Without either dialysis or a transplant, dangerous levels of fluid, potassium, and waste products build up, eventually leading to heart failure, coma, and death. Dialysis is not a cure; it replaces about 10 to 15% of normal kidney function, enough to keep you alive but not enough to make you feel entirely well.
What Life on Dialysis Looks Like
Dialysis keeps you alive, but it reshapes daily life. Hemodialysis patients spend 12 or more hours a week connected to a machine, plus travel time to and from a clinic. Fatigue after sessions is common, and many people describe feeling “washed out” for hours afterward. Diet restrictions are significant: you’ll need to limit potassium, phosphorus, sodium, and fluid intake carefully, since dialysis only partially compensates for what healthy kidneys do continuously.
Peritoneal dialysis offers more day-to-day flexibility but requires strict hygiene to prevent infection around the catheter. Both types carry risks including infection, blood pressure drops during treatment, and long-term cardiovascular strain. Despite these challenges, many people work, travel, and maintain active lives on dialysis. The treatment has kept millions of people alive who would have had no options a few decades ago.