Dialysis is a medical technique that allows people with damaged kidneys to have waste products from their blood removed, mimicking what a healthy kidney would do. The efficiency of dialysis is typically monitored, to check that the affected person is treated in the best way possible. Measuring this efficiency is called checking dialysis adequacy, and there are two main ways in which to do this. These methods both involve removing and analyzing blood for waste products before and after dialysis sessions. Alternatively, the patient's urine may be analyzed for waste products to assess dialysis adequacy.
Waste products in the body normally leave the body in urine, in feces or in exhaled breath. When the kidneys are damaged, their ability to sort waste from the blood reduces, and the person may then require dialysis. Instead of the waste products in the blood filtering through the kidneys, they are filtered artificially through a machine. This machine removes waste like urea and excess water from the blood, and returns the filtered blood back to the person's body.
Each individual person undergoing dialysis has differing levels of waste and excess water removed from the body. This is due to various factors, such as the size of the person and the rate at which the blood flows trough the body and through the machine. Tweaks of the dialysis routine are therefore sometimes necessary to give the patient the best rate of waste clearance from blood, and so give him or her the best treatment possible.
Checks of the efficiency of a particular dialysis routine are referred to as dialysis adequacy checks, as each individual's dialysis adequacy is achieved with different routines. A nurse or doctor can use two different major techniques to assess dialysis adequacy, both of which are based on the concentration of waste products in the blood at particular points in the dialysis regimen. One is called urea reduction ratio (URR), and is calculated by comparing the concentration of urea, which is a waste product, in the blood of the patient before and after dialysis. This directly represents the efficiency of the dialysis machine at clearing waste from the blood.
The other is a calculation expressed as Kt/V. In this equation, the "k" represents the rate at which blood moves through the dialyzer, "t" represents time, and "V" represents the volume of water in the patient's body. This entire calculation represents the blood volume that is cleaned during a particular session of dialysis. Both of these methods of checking dialysis adequacy can be used to help tweak the dialysis routine of the patient.
For example, a low Kt/V can indicate that the person may benefit from longer periods of time on the dialysis machine. A URR result of less than about 60 percent generally also indicates that the type of dialysis the person is undergoing is not sufficient. For patients who still produce urine, the levels of waste products in the urine may also be tested to assess the adequacy of dialysis. Dialysis removal of waste is important for the health of people with kidney problems, as the body's waste products become toxic at high levels.