Dialysis is a treatment that takes over the filtering work your kidneys can no longer do. When kidney function drops below about 15% of normal, your body can’t adequately remove waste products, excess fluid, and toxins from your blood on its own. Dialysis steps in to handle that job, keeping the chemical balance in your blood stable enough to sustain life.
How Dialysis Filters Your Blood
Healthy kidneys filter your entire blood supply dozens of times a day, pulling out waste and extra water while keeping blood cells and proteins where they belong. Dialysis mimics this process using three physical principles: diffusion, convection, and osmotic pressure.
In diffusion, your blood is brought close to a clean fluid called dialysate, separated only by a thin wall known as a semipermeable membrane. Waste particles naturally drift from the blood (where they’re concentrated) across the membrane into the dialysate (where they’re scarce), the same way a tea bag colors the water around it. The membrane’s tiny pores block blood cells and other essential components from crossing over.
Convection uses pressure to push water out of the blood, carrying dissolved waste along with it. Some methods also rely on osmotic pressure, where sugar in the dialysate draws excess water out of the blood. Together, these mechanisms clear toxins and regulate fluid levels, though they replace only a fraction of what healthy kidneys accomplish around the clock.
The Two Main Types
Hemodialysis
Hemodialysis routes your blood through an external machine that acts as an artificial kidney. Blood leaves your body through a needle, passes through a filter containing that semipermeable membrane, and returns cleaned. Most people receive hemodialysis three times a week at a clinic, with each session lasting 3 to 5 hours. Home hemodialysis is also an option for some patients, sometimes on a more frequent schedule.
To connect you to the machine, you need a reliable access point in your bloodstream. There are three types. An arteriovenous (AV) fistula is a surgical connection between an artery and a vein, usually in the forearm. It takes weeks to months to mature before it can be used, and sometimes requires additional procedures, but it carries the lowest infection risk. An AV graft uses a synthetic tube to make the same connection and is an alternative when a fistula isn’t possible. Catheters, placed in a large vein in the neck or chest, are used when neither a fistula nor graft is ready. Catheters carry the highest infection risk. Compared to fistulas, catheters roughly double the risk of fatal infection and raise the risk of nonfatal infection nearly fivefold.
Peritoneal Dialysis
Peritoneal dialysis uses the lining of your abdomen (the peritoneum) as the natural filter instead of an external machine. A permanent catheter placed in your abdomen allows dialysate to flow in and sit there for several hours, absorbing waste through the blood vessels in the peritoneal lining. Then the fluid drains out, and fresh dialysate goes in.
There are two approaches. Continuous ambulatory peritoneal dialysis (CAPD) is done manually throughout the day, typically exchanging about 2 to 2.5 liters of fluid at a time, with each fill sitting for 4 to 10 hours. You do the exchanges yourself, no machine required. Automated peritoneal dialysis (APD) uses a machine called a cycler that performs faster exchanges overnight while you sleep. Both approaches offer more flexibility than in-center hemodialysis, and many people prefer them for the independence they allow.
When Dialysis Becomes Necessary
Most guidelines recommend starting dialysis before kidney filtration rate drops below 6 milliliters per minute, a level considered potentially dangerous. Broader guidelines suggest planning for dialysis when filtration falls below 15 mL/min, especially if symptoms are present. But the decision isn’t based on a single number alone.
Certain symptoms push the timeline forward regardless of lab values: fluid buildup that causes swelling or breathing problems, persistent nausea and vomiting that don’t respond to medication, confusion or declining mental sharpness, uncontrolled high blood pressure, or a general and severe drop in quality of life. Some people with conditions like diabetes may need to start sooner. The goal is to begin before these complications become life-threatening, not to wait for a crisis.
What a Session Feels Like
Dialysis sessions aren’t painful in themselves, but they do come with side effects. The most common issues during or shortly after hemodialysis include drops in blood pressure, muscle cramps, and dizziness, particularly toward the end of a session. A condition called disequilibrium syndrome can cause headaches, nausea, blurred vision, restlessness, or confusion, usually starting soon after treatment begins. These symptoms happen because waste is removed from the blood faster than it can shift out of brain tissue, creating a temporary fluid imbalance. In most cases, symptoms are mild and resolve within hours. Severe reactions like seizures are rare.
Fatigue is the side effect people notice most in their daily lives. Many hemodialysis patients feel washed out for hours after a session, and the three-times-a-week schedule structures much of the week around treatment. Peritoneal dialysis tends to cause fewer dramatic swings in how you feel, since it runs more continuously, but it carries its own risk of abdominal infections at the catheter site.
Dietary Changes on Dialysis
Your kidneys normally regulate potassium, phosphorus, sodium, and fluid balance automatically. On dialysis, that regulation only happens intermittently, so what you eat and drink between sessions matters significantly. Most people on hemodialysis work with a renal dietitian to set individualized daily limits on fluid intake and specific nutrients. Dairy is typically limited to about half a cup of milk per day because of its phosphorus content. Potassium-rich foods like bananas, oranges, and potatoes often need to be reduced. Sodium restriction helps control thirst and fluid retention between sessions.
These restrictions feel burdensome at first, but they directly affect how you feel. Too much fluid between sessions means more has to be removed during treatment, which increases the likelihood of blood pressure drops and cramping. Excess potassium can cause dangerous heart rhythm problems. A dietitian tailors these limits to your specific lab results and treatment schedule.
Life Expectancy and Outcomes
Dialysis sustains life, but it doesn’t restore full health. According to 2022 data from the U.S. Renal Data System, a 45- to 49-year-old woman on dialysis has about 8.1 expected remaining years of life, compared to 35.1 years for a woman the same age in the general population. A man aged 65 to 69 on dialysis has roughly 4.5 remaining years, compared to 15.9 for the general population. Five-year survival after starting hemodialysis is about 41%, a figure that has remained essentially unchanged between 2008 and 2018 cohorts.
Kidney transplantation dramatically improves these numbers. For a woman aged 55 to 59, transplantation is associated with a survival advantage of about 10 years compared to remaining on dialysis. For a similarly aged man, the advantage is roughly 8.7 years. Not everyone is a candidate for transplant, and wait times for a donor kidney can stretch for years, but it remains the treatment most likely to restore something close to normal life expectancy.
One pattern in the data is striking: five-year survival rates differ significantly by race. Among people on peritoneal dialysis, Black individuals in the 2018 cohort had a five-year survival rate of 48.4%, compared to 36.0% for White individuals. The reasons for this gap are still being studied, but it appears consistently across multiple datasets.
Living on Dialysis Day to Day
People on in-center hemodialysis typically spend 9 to 15 hours per week in a dialysis chair, plus travel time. Many continue to work, though scheduling around sessions requires flexibility. Peritoneal dialysis allows more freedom during the day, especially the automated overnight version, but it requires a clean space at home and the discipline to manage supplies and exchanges consistently.
Travel is possible on both types of dialysis, though it requires planning. Hemodialysis patients can arrange sessions at clinics in other cities, and peritoneal dialysis supplies can be shipped to a destination ahead of time. Exercise is encouraged and generally safe. Physical activity on dialysis has been linked to better energy levels, appetite, and sleep, though the intensity needs to match how you’re feeling on any given day.