How Does Renal or Kidney Dialysis Work?

Dialysis machine & patient
A woman undergoes renal or kidney dialysis. Photo © Science Photo Library/Brand X Pictures/Getty Images

Renal or kidney dialysis is a process used to filter impurities from human blood using a dialysis machine (dialyzer) when an individual's kidneys are no longer healthy enough to perform this function. (The word renal derives from the Latin term "ren," meaning kidney.)

Normally, human kidneys remove excess salt, water and other toxic waste products from the blood, which helps the body maintain the appropriate levels of important chemicals and minerals and helps maintain proper blood pressure.

When the kidneys don't work properly, or if chronic or end-stage kidney failure occurs, then the patient will require dialysis.

Whether performed in a hospital, clinic or even at home, the process generally involves the insertion of a thin plastic tube, called a catheter, into an artery. During dialysis, the blood flows through this arterial catheter into the dialyzer, where it is filtered/cleansed, before returning into the body via the venous catheter, a second thin plastic tube inserted into a vein.

Renal dialysis can be used temporarily to allow the kidneys to heal from certain acute, short-term problems, but if chronic or end-stage kidney failure has occurred, the patient will require dialysis for life unless he or she receives a kidney transplant.


Renal dialysis is also known as kidney dialysis or hemodialysis. (Another form of dialysis, known as peritoneal dialysis, cleanses the blood when the kidneys cannot but does so internally, i.e., within the patient's abdomen.)

Edited and updated by Chris Raymond, June 3, 2015.

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