Water Testing In Renal Dialysis
Chlorine and Renal Dialysis
Chlorine and related disinfectants such as chlorine dioxide are generally treated as “undesirable” in renal units.
This is because chlorine attacks the semi-permeable membranes where the exchange of waste products between the patient’s blood and the dialysate takes place. Chlorine damage typically increases the size of the pores in the membrane and the chlorine itself eventually moves through the membrane in to the patient’s bloodstream. This is fairly catastrophic and causes haemolysis (rupture of red blood cells).
However, there is also a need to disinfect the medical equipment, tubing and machinery used in dialysis treatment. High levels of Chlorine can therefore be useful for this, but it is then important to remove this thoroughly by rinsing with purified water. Then test for the presence of chlorine.
How is Chlorine removed from Renal Dialysis Water?
Renal dialysis units invest large amounts of money trying to remove chlorine from the feedwater they use to generate dialysis fluid.
Typically, incoming water passes through a water softener; is then filtered through activated carbon and then passes to a reverse osmosis process. This should remove all contaminants (including chlorine) from the water which then has a very low conductivity. Typically this is measured continuously. This water is then circulated in an isolated loop around the renal unit.
The loop water is then tested regularly for chlorine to ensure that there is always an extremely low level or complete absence. Testing for the absence of an analyte such as chlorine requires awareness of the limit of detection of the test method being used and the specificity of the method.
What are the Guidelines for Chlorine Levels in Renal Dialysis Water?
ISO 23500:2019 is widely accepted for guidance on consent limits and testing chlorine in renal dialysis water, however regulations can vary globally. According to this standard the maximum consent limit for chlorine is 0.1 mg/L total chlorine.
The standard refers to the total chlorine level. It is important to understand the difference between total, free and combined chlorine as this can help when deciding which test method to use.
What Methods are Used to test Water used for Renal Dialysis?
Test Strips
Test strips have been the standard method for measuring chlorine in many countries for many years as they are easy to use and require little investment.
However, test strips are limited in resolution to a small number of discrete steps. Not all brands are designed for use in renal applications where the chlorine levels are very low. This increases the chances of false negative results. Testing is further complicated by the often small visible colour differences between graduations i.e. pads at 0 mg/L chlorine and 0.1 mg/L chlorine may be very similar in colour.
DPD Colorimetric Method
DPD reagents are an alternative to test strips when measuring chlorine in water samples. When used with a photometer, the method is less dependent on human interpretation, eyesight and colour vision. In ISO 23500, the DPD colorimetric method is stated as a suitable method and is used in the UK.
DPD reagents are an alternative to test strips when measuring chlorine in water samples. When used with a photometer, the method is less dependent on human interpretation, eyesight and colour vision. In ISO 23500, the DPD colorimetric method is stated as a suitable method and is used in the UK.
Inline chlorine meters that use DPD are an alternative option. However, these are expensive and require regular maintenance and attention.
Kemio Disinfection
Test Strips
Kemio™ is a multiparameter measurement platform from Palintest. It uses a sophisticated, non-subjective electrochemical method with disposable sensors to measure chlorine concentration in a water sample. The Kemio™ method is US EPA approved, with a detection limit of 0.02 mg/L for total chlorine, which is below the consent limit of 0.1 mg/L.
- Kemio™ will measure free and total chlorine at the same time with ease, meaning that combined chlorine levels can be monitored more closely.
- Kemio™has a truly simple, 4-step method meaning no user training is required. An instructional video is available.
- The Kemio™ instrument can store up to 10000 test results with all test information making for complete traceability of results.
- There is no glassware or chemical reagents required.
Chlorine Dioxide
Chlorine dioxide is often added to incoming water in large buildings such as hospitals. This is because the incoming mains water may become depleted of chlorine when it is distributed over large networks of piping within buildings. There is then a particular risk of legionella, especially on the hot water distribution system.
Chlorine Dioxide is used because it is easy to manufacture in situ. It is also a particularly effective disinfectant. It works well against biofilms and tends to produce fewer disinfection byproducts than chlorine.
In addition to chlorine Kemio™ Disinfection can also test for chlorine dioxide and chlorite which is used as a precurser chemical in the dosing process and also needs to kept withing a maximum limit.