Plasmapheresis works by drawing your blood out of your body, separating the liquid portion (plasma) from the blood cells, discarding or filtering that plasma, and then returning the blood cells along with a replacement fluid. The entire process takes about two to three hours per session, and a typical course involves four to five sessions. It’s used to physically remove harmful antibodies, immune complexes, and other disease-causing proteins that are dissolved in your plasma.
Two Ways to Separate Plasma From Blood Cells
There are two main techniques for splitting plasma away from blood cells, and they work on different physical principles.
Centrifugation spins your blood at high speed. Because red blood cells, white blood cells, platelets, and plasma all have different densities, centrifugation pushes heavier components outward while lighter plasma collects separately. The machine discards the plasma entirely and returns your blood cells mixed with a replacement fluid. This method extracts about 80% of the plasma from the blood passing through the circuit, and it works at relatively low blood flow rates of 10 to 150 milliliters per minute. That’s slow enough that many patients can use a standard peripheral IV in their arm rather than a larger catheter.
Membrane filtration pushes blood through a semipermeable membrane with pores sized to let plasma proteins pass through while holding back blood cells. This approach can be more selective: instead of throwing out all the plasma, it can target specific large molecules (those above a certain size) while keeping smaller, beneficial proteins. Because the plasma is filtered and processed rather than fully discarded, patients receiving membrane filtration sometimes don’t need replacement fluid at all. Membrane filtration requires higher blood flow rates, typically 150 to 200 milliliters per minute, which usually means a larger-bore catheter.
What Replacement Fluids Do
When centrifugation-based plasmapheresis discards your plasma, that lost volume needs to be replaced. The two main options are a 5% albumin solution and fresh frozen plasma (FFP) from donors, and the choice depends on your specific condition.
Albumin is the most common replacement fluid, used in roughly 71% of procedures either alone or mixed with saline or other fluids. It replaces the volume and maintains your blood pressure without introducing immune proteins. Fresh frozen plasma is reserved for situations where you need something plasma naturally contains. In thrombotic thrombocytopenic purpura (TTP), for example, patients are missing a critical enzyme that breaks down blood-clotting proteins. Donor plasma supplies that enzyme directly, so it serves a therapeutic purpose beyond simple volume replacement. FFP is also preferred when there’s a high bleeding risk, such as before major surgery, because it contains clotting factors that albumin lacks.
Each replacement fluid carries different trade-offs. Albumin is associated with drops in blood pressure during the procedure. Donor plasma carries a small risk of allergic reactions and, very rarely, transfusion-related acute lung injury. Anaphylactic reactions to donor plasma are the most common cause of serious complications during plasma exchange, reported in up to 21% of patients receiving plasma as a replacement fluid. These reactions range from fever and hives to wheezing and dangerous drops in blood pressure.
Why Removing Plasma Treats Disease
The therapeutic logic is straightforward: if a disease is driven by something dissolved in your plasma, physically removing that plasma removes the disease driver. The targets include autoantibodies (antibodies your immune system mistakenly makes against your own tissues), circulating immune complexes (clumps of antibodies bound to other molecules that deposit in organs and cause inflammation), and other large proteins that are fueling a disease process.
The American Society for Apheresis recognizes 166 separate indications across 91 disease categories where plasma exchange has evidence supporting its use. Some of the most well-established include Guillain-Barré syndrome (where antibodies attack the nerves), myasthenia gravis (where antibodies block signals between nerves and muscles), and TTP. In Guillain-Barré syndrome, a standard course of four to five sessions removes enough pathogenic antibodies to allow nerve recovery, with patients reaching maximum improvement in roughly six to seven weeks.
What a Session Feels Like
Each session typically lasts two to three hours. You’ll be seated or reclined while blood is drawn from one access point, run through the machine, and returned through the same or a second access point. Most patients undergoing a short course of treatment use a central venous catheter, a large IV line placed in the neck, chest, or groin. For people who need ongoing, repeated treatments over months or years, a surgically created connection between an artery and vein in the arm (similar to what dialysis patients use) provides more durable access with lower infection risk, though these are used in only 2% to 4% of apheresis procedures because they take weeks to mature.
During the procedure, the machine processes roughly 1.5 to 2 times your total blood volume. Only a small amount of blood is outside your body at any given time, around 180 milliliters in a centrifuge-based system, so the process isn’t as dramatic as it sounds. You’re awake throughout and can read, watch something, or rest.
Side Effects During and After Treatment
The most common side effect is tingling or numbness around your mouth and fingertips, caused by the anticoagulant used to keep blood from clotting inside the machine. That anticoagulant, sodium citrate, works by binding to calcium in your blood. When it lowers your calcium levels too much, you feel pins-and-needles sensations, and in more pronounced cases, muscle cramps, nausea, or chest tightness. Medical teams monitor for this and can slow the procedure or give calcium supplements to counteract it. Severe reactions like dangerous heart rhythm changes are rare.
Other possible complications include low blood pressure (especially with albumin replacement), allergic reactions (especially with donor plasma), and catheter-related issues like infection or bleeding at the insertion site. Metabolic alkalosis, a shift in blood chemistry toward being too basic, can also occur from the citrate.
Effects of Repeated Treatment on Immunity
Because plasmapheresis removes plasma proteins indiscriminately, repeated sessions lower your levels of immunoglobulins, the antibodies your body uses to fight infections. This is an expected consequence, and it raises a reasonable concern: does stripping out antibodies leave you vulnerable to getting sick?
A large prospective study of repeat plasma donors found that while immunoglobulin levels did decline over time, particularly in those who started with higher levels, the drop did not translate into more infections or serious side effects. Donors whose antibody levels fell below the normal threshold on three or more occasions actually had lower rates of infection than those whose levels stayed above the threshold. The study concluded that plasmapheresis remained safe even in people with persistently low immunoglobulin measurements. For patients receiving therapeutic plasmapheresis for a disease, the courses are typically short enough (five sessions over one to two weeks) that long-term immune suppression is not a major concern, though your medical team will monitor your levels if treatment extends over months.