Yes, dialysis removes sodium from your body, and it’s one of the treatment’s most important jobs. Healthy kidneys constantly filter excess sodium out through urine, so when they stop working, sodium builds up in your blood, pulls in extra fluid, and raises blood pressure. Dialysis steps in to restore that balance, though how well it works depends on the type of dialysis, the machine settings, and how much sodium you take in between sessions.
How Hemodialysis Removes Sodium
During hemodialysis, your blood flows through a filter (the dialyzer) while a cleansing fluid called dialysate runs alongside it, separated by a thin membrane. Sodium crosses that membrane through two processes: convection and, to a lesser degree, diffusion.
Convection is the bigger contributor. When the machine pulls excess fluid out of your blood (a process called ultrafiltration), sodium dissolved in that fluid gets dragged along with it. Think of it like water flowing through a coffee filter and carrying dissolved particles with it. Diffusion works differently: if your blood sodium level is higher than the sodium level in the dialysate, sodium naturally drifts across the membrane from the more concentrated side to the less concentrated side, evening things out.
The net amount of sodium removed in a session depends on the interplay between these two forces and, critically, on how the dialysate is formulated.
Why the Dialysate Sodium Setting Matters
Dialysate fluid is not pure water. It contains sodium and other electrolytes at carefully chosen concentrations. In standard practice, dialysate sodium is set somewhere in the range of 136 to 140 mmol/L, with the goal of roughly matching your blood sodium level. This approach, sometimes called isonatric dialysis, removes sodium primarily through convection as fluid is pulled off, without creating a large push or pull of sodium through diffusion.
When the dialysate sodium is set lower than your blood sodium, the gradient favors more sodium removal through diffusion on top of what convection already pulls out. That sounds like a good thing, but it comes with trade-offs. A clinical trial comparing dialysate sodium of 135 versus 138 mEq/L found that the lower setting increased symptoms like headache, nausea, drowsiness, muscle twitching, and blurred vision. About 7 to 10 percent of patients in the lower-sodium groups across studies couldn’t tolerate it and had to stop. Raising dialysate sodium from 135 to 140 mEq/L reduced episodes of low blood pressure during treatment by roughly 34 percent.
On the flip side, when dialysate sodium is set higher than your blood sodium, sodium actually diffuses into your body during the session. This increases the concentration of dissolved particles in your blood, which triggers thirst. You drink more between sessions, gain more fluid weight, and may end up with higher blood pressure. It essentially trades a more comfortable session for worse outcomes between treatments.
The Thirst and Weight Gain Cycle
One of the most practical things to understand about sodium and dialysis is the cycle it creates between sessions. If dialysis doesn’t remove enough sodium, or if you eat a lot of salty food between treatments, your blood becomes more concentrated. Your body responds the only way it can: making you thirsty so you’ll drink water and dilute things back to normal. But without working kidneys, that extra fluid has nowhere to go. It accumulates, causing swelling, weight gain, and strain on your heart.
Research shows that the gap between your blood sodium level and the dialysate sodium level before a session (called the pre-dialysis sodium gradient) is one of the strongest predictors of how much fluid weight you gain between treatments. People with diabetes on hemodialysis are especially vulnerable because high blood sugar compounds the thirst effect, and less effective sodium clearance during their sessions makes the cycle worse. In studies of this group, the pre-dialysis sodium gradient and saliva flow rate were the only two independent predictors of excessive weight gain between sessions.
Chronic fluid overload from this cycle is not just uncomfortable. It’s a major driver of cardiovascular complications, which remain the leading cause of death in people on dialysis.
How Peritoneal Dialysis Handles Sodium
Peritoneal dialysis works differently. Instead of filtering blood through an external machine, it uses the lining of your abdomen as a natural membrane. A sugar-based solution is infused into the abdominal cavity, and waste products and excess fluid cross from the blood vessels in that lining into the solution.
Sodium removal in peritoneal dialysis involves a unique phenomenon called sodium sieving. When fluid is pulled across the peritoneal membrane, a significant portion of it (roughly 40 to 50 percent) crosses as free water, meaning water without sodium. This dilutes the sodium concentration in the dialysate fluid sitting in your abdomen, creating a measurable dip in dialysate sodium during the first hour of a dwell. The size of that dip is proportional to how fast fluid is being pulled across, and clinicians can use it as a marker of how well the treatment is working.
Because so much of the fluid transfer is sodium-free water, peritoneal dialysis can struggle to remove enough sodium overall. Inadequate sodium removal leads to sodium retention, fluid buildup, and volume overload, a recognized challenge for people on this form of dialysis.
Dietary Sodium and Dialysis Working Together
Dialysis can only do so much. A typical hemodialysis session happens three times a week for about four hours, and even under ideal conditions, the machine can’t fully compensate for a high-sodium diet consumed over the days between sessions. That’s why dietary sodium restriction is a cornerstone of managing kidney failure.
The National Kidney Foundation recommends no more than 2 grams (2,000 milligrams) of sodium per day for people on hemodialysis, with reductions also recommended for those on peritoneal dialysis. For reference, a single teaspoon of table salt contains about 2,300 milligrams of sodium, and the average American diet contains over 3,400 milligrams per day. Staying within the recommended range means reading labels carefully and cooking most meals at home, since restaurant and processed foods are the biggest sources of hidden sodium.
Keeping sodium intake low between sessions reduces thirst, limits fluid weight gain, and makes each dialysis treatment more effective at maintaining a healthy fluid balance. It also gives your care team more flexibility in setting the dialysate sodium at a level that keeps you comfortable during treatment without loading you up with extra sodium in the process.