Dialysis is a medical treatment that takes over the essential filtering work of your kidneys when they can no longer do it themselves. Its primary use is treating advanced kidney failure, where it removes waste products, excess fluid, and toxic substances from the blood. Most people who need dialysis have Stage 5 chronic kidney disease, meaning their kidneys are functioning at less than 15% of normal capacity. In some cases, dialysis is also used in emergencies like poisoning or drug overdose to pull dangerous substances out of the bloodstream.
How Dialysis Replaces Kidney Function
Healthy kidneys filter about 50 gallons of blood every day, pulling out waste, balancing minerals, and removing extra fluid. When kidney function drops low enough, these waste products build up in your blood and start causing symptoms: nausea, fatigue, swelling, confusion, and eventually life-threatening complications. Dialysis steps in by running your blood past a special membrane that mimics what your kidneys do naturally.
The core process relies on two physical principles. The first is diffusion: waste molecules in your blood naturally move across the membrane toward cleaner fluid (called dialysate) on the other side, the same way a tea bag releases flavor into hot water. The second is ultrafiltration, where pressure differences across the membrane push excess water out of your blood. Together, these two processes clean your blood and reduce fluid buildup that would otherwise strain your heart and lungs.
Conditions That Require Dialysis
The vast majority of people on dialysis have chronic kidney disease that has progressed to its most advanced stage. At this point, the kidneys can no longer keep up with the body’s needs, and waste products accumulate to dangerous levels. Doctors don’t start dialysis based on a single lab number alone. The decision depends on whether you’re experiencing symptoms of kidney failure and whether dialysis can relieve them.
Those symptoms can include persistent nausea, severe fatigue, mental fogginess, swelling in the legs and feet, and difficulty breathing. Some people develop dangerous shifts in blood chemistry: potassium levels that climb high enough to cause heart rhythm problems, acid buildup that weakens bones and muscles, or phosphorus levels that pull calcium out of bones and deposit it in blood vessels. When dietary changes and medications can no longer control these problems, dialysis becomes necessary.
Dialysis is also used in acute situations. In emergency rooms, it can remove certain poisons and drug overdoses from the bloodstream. The most common toxins treated this way are lithium and ethylene glycol (antifreeze). It has also been used for overdoses of certain seizure medications and mood stabilizers, though it isn’t effective for every type of poisoning.
The Two Main Types
Hemodialysis
Hemodialysis is the most common form. Your blood is drawn out through a needle, passed through an external filtering machine, and returned to your body. The conventional schedule is three sessions per week, each lasting three to five hours. Most people receive treatment at a dialysis center, where trained staff handle every aspect of the process and other patients are dialyzing at the same time.
Home hemodialysis is another option, typically done five to seven times per week in shorter sessions. You and a trained partner learn to operate the equipment yourselves. This requires dedicated space in your home for the machine and supplies, and may need modifications to your plumbing or electrical system. The tradeoff is greater flexibility and the comfort of being at home.
Peritoneal Dialysis
Peritoneal dialysis uses the lining of your abdomen as the filter instead of an external machine. A sugar-based solution is pumped into your abdominal cavity through a small permanent catheter. The sugar draws waste and excess fluid across the abdominal lining and into the solution, which is then drained out. No needles or machines are required, and you do it every day at home. Different concentrations of sugar in the solution (1.5%, 2.5%, or 4.25%) control how much fluid gets removed. Many people find peritoneal dialysis allows more mobility and makes travel easier, though you’ll need storage space at home for supplies.
What Dialysis Manages in Your Blood
Beyond filtering waste, dialysis helps regulate several critical minerals that your kidneys would normally control.
- Potassium: When potassium levels swing too high or too low, your heart can develop dangerous rhythm problems. The dialysis solution can be adjusted to bring potassium into a safe range, and some people also take medications between sessions to keep levels stable.
- Sodium and fluid: Excess sodium causes your body to hold onto water, raising blood pressure and putting stress on your heart. Dialysis removes this extra fluid, but patients are also advised to keep sodium intake below 2,300 milligrams per day between treatments to prevent fluid from accumulating too quickly.
- Phosphorus: Hemodialysis does not remove phosphorus effectively. High phosphorus weakens bones and can combine with calcium to form deposits in blood vessels and the heart. Most dialysis patients take phosphorus-binding medications with meals to compensate.
- Acid balance: Failing kidneys allow acid to build up in the body, which damages bones, muscles, and any remaining kidney function. The dialysis solution contains bicarbonate to neutralize this excess acid.
What Dialysis Cannot Do
Your kidneys are not just filters. They also produce hormones, and dialysis cannot replicate that function. The most significant gap is a hormone that signals your bone marrow to produce red blood cells. As kidney function declines, production of this hormone drops, leading to anemia. This is common in dialysis patients and contributes to the fatigue and weakness many people feel. It’s typically treated with injections that stimulate red blood cell production, but it’s an ongoing problem that dialysis itself doesn’t solve.
Kidneys also play roles in regulating blood pressure, activating vitamin D for bone health, and fine-tuning other hormonal signals. Dialysis addresses none of these, which is why people on dialysis often take multiple medications to fill the gaps. A kidney transplant, when available, is the only treatment that fully restores all kidney functions.
Life on Dialysis
Dialysis is a lifelong commitment unless you receive a kidney transplant. The time investment is significant: in-center hemodialysis requires traveling to a clinic three days a week and spending several hours connected to a machine each visit, with your schedule set by the center. Peritoneal dialysis offers more daily flexibility but never gives you a day off.
Survival rates have improved over the past two decades. Median survival for people starting hemodialysis rose from about 37 months in 2003 to 47 months by 2013. Mortality rates for people on peritoneal dialysis are somewhat lower than for those on hemodialysis. Between 2009 and 2018, the annual death rate for peritoneal dialysis patients dropped from about 164 to 132 per thousand patients, compared to a decrease from 193 to 165 per thousand for hemodialysis patients.
Still, the health impact is substantial. Among people in their early 40s on dialysis, life expectancy is more than 25 years shorter for men and more than 30 years shorter for women compared to the general population. The first year after starting dialysis carries the highest risk, though that risk has also been declining over time. These numbers reflect the severity of kidney failure itself, not just the treatment. Dialysis keeps people alive and functioning, but it replaces only a fraction of what healthy kidneys provide.