Dialysis is a medical treatment that does the work of your kidneys when they can no longer filter waste and excess fluid from your blood on their own. Healthy kidneys clean about 200 liters of blood every day, but when kidney function drops to roughly 15% or less of normal, toxins build up in the bloodstream and the body can’t maintain its chemical balance. Dialysis steps in to remove those waste products, restore safe levels of key minerals, and pull out extra fluid that would otherwise cause dangerous swelling and high blood pressure.
How Dialysis Filters Your Blood
Your kidneys filter blood through millions of tiny structures that sort waste from the things your body needs. Dialysis mimics this process using a semipermeable membrane, a thin barrier full of microscopic pores that lets small molecules pass through while blocking larger ones like blood cells and proteins.
Two physical forces do the heavy lifting. The first is diffusion: waste molecules in your blood are at a higher concentration than in the clean dialysis fluid on the other side of the membrane, so they naturally drift across to the cleaner side. Small molecules like urea move fastest. The second force is convective clearance, where water pushed through the membrane drags dissolved waste products along with it, much like a current carrying debris downstream.
The dialysis fluid itself is carefully designed to make this work. It contains sodium, potassium, calcium, magnesium, bicarbonate, and glucose at concentrations close to what healthy blood should have, but it contains none of the waste products that accumulate when kidneys fail. That concentration difference is what drives toxins out of the blood and into the fluid for disposal.
When Dialysis Becomes Necessary
Kidney function is measured by the glomerular filtration rate (GFR), a number that reflects how efficiently your kidneys clean your blood each minute. A GFR of 60 or higher is normal. Below 60 signals kidney disease. A GFR of 15 or lower indicates kidney failure, the point at which dialysis or a transplant typically becomes necessary.
What makes kidney disease tricky is that most people have no symptoms until their kidneys are close to failing. By the time you notice fatigue, nausea, swelling in your legs, or difficulty concentrating, a large portion of kidney function is already gone. That’s why routine blood and urine tests matter, especially if you have diabetes, high blood pressure, or a family history of kidney problems.
The Two Main Types of Dialysis
Hemodialysis
Hemodialysis routes your blood through a machine that contains the filtering membrane. Blood leaves your body through a special access point, passes through the filter where waste and fluid are removed, and returns cleaned. Most people who do in-center hemodialysis go three times per week, with each session lasting three to five hours.
Before hemodialysis can begin, you need a reliable way to move blood in and out of your body quickly. The preferred option is an arteriovenous fistula, a surgical connection between an artery and a vein (usually in the arm) that causes the vein to enlarge and strengthen. A fistula needs about six to eight weeks to mature before it can be used. If a fistula isn’t possible, a synthetic graft serves a similar purpose. As a last resort, a catheter placed in a large vein in the neck or chest provides immediate access but carries a higher infection risk.
Peritoneal Dialysis
Peritoneal dialysis uses the lining of your abdominal cavity as the filter instead of an external machine. A permanent catheter is placed in your abdomen, and sterile dialysis fluid flows in through it. The fluid sits inside for several hours (called a dwell), during which waste and extra water cross from the blood vessels in your abdominal lining into the fluid. Then the fluid is drained and replaced.
There are two approaches. Continuous ambulatory peritoneal dialysis (CAPD) is done manually: you fill your abdomen, go about your day for several hours, then drain and refill. You repeat this cycle multiple times throughout the day. Automated peritoneal dialysis (APD) uses a programmable machine called a cycler that performs the exchanges automatically while you sleep, sometimes with one longer daytime dwell. Many people prefer APD because it frees up daytime hours for work and normal activities.
Home Dialysis vs. In-Center Treatment
Most hemodialysis patients receive treatment at a dialysis center, where nurses and technicians manage the equipment. But home hemodialysis is a growing option that allows for longer, gentler sessions. In one large multicenter study, home hemodialysis patients averaged about seven hours per session compared to roughly four hours in-center, and that slower filtration made a meaningful difference in outcomes.
Home hemodialysis was associated with a 40% lower risk of death compared to conventional in-center treatment. Patients also had better blood pressure control, lower phosphorus levels, improved nutrition markers, fewer days in the hospital, and needed fewer medications. After five years, 86.5% of home patients were still successfully managing their treatment at home. Home dialysis isn’t right for everyone, as it requires training, space, and a degree of comfort with the equipment, but for those who can manage it, the benefits are substantial.
What Life on Dialysis Looks Like
Dialysis replaces kidney function, but it doesn’t do so perfectly. Your diet will need to change. Most dialysis patients are advised to keep phosphorus intake below 800 milligrams per day and potassium below 3,000 milligrams per day, since the kidneys normally regulate both. High-phosphorus foods include dairy, processed meats, and colas. High-potassium foods include bananas, oranges, potatoes, and tomatoes. Fluid intake is also restricted because the kidneys can no longer remove excess water between sessions.
The most common short-term side effect of hemodialysis is a drop in blood pressure during treatment, which can cause dizziness, nausea, or cramping. This happens because fluid is being removed from the bloodstream faster than the body can compensate. Adjusting the rate of fluid removal or changing the dialysis fluid composition usually helps.
Long-Term Complications
Over years of treatment, dialysis can trigger a condition where a specific protein accumulates in joints and bones. This primarily affects the shoulders, wrists, and cervical spine. Carpal tunnel syndrome is one of the most recognizable early signs: pain, numbness, and tingling in the thumb and first three fingers. Over time, bone cysts can form in the wrists, hips, and shoulders, and some patients develop destructive changes in the spinal discs of the neck. These complications become more common the longer someone remains on dialysis, particularly beyond 10 to 20 years.
Survival and Outlook
Dialysis is a life-sustaining treatment, but it does not restore full health. According to data from the U.S. Renal Data System, about 41% of hemodialysis patients survive five years after starting treatment. For peritoneal dialysis, the five-year survival rate is roughly 42.5%. These numbers have remained relatively stable over the past decade, with modest improvements in older patients but little change overall.
Age, diabetes, heart disease, and overall health at the time dialysis begins all heavily influence individual outcomes. Younger patients and those without significant cardiovascular disease tend to fare much better than the averages suggest. A kidney transplant, when available, generally offers better long-term survival and quality of life than continued dialysis, which is why many dialysis patients are simultaneously on a transplant waiting list.