College of American Pathologists
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Checking for silicates

May 2001

Not discipline-specific but relatively new is a checklist question "that has been throwing people," Dr. Ruhlen says. "They didn’t realize it was in there and they were getting cited on it."

Question 01:4165 from the laboratory general checklist asks, "Has the laboratory evaluated its source water to determine if a high concentration of silicates is present?"

Like other water quality testing, checking for silicates is important because elevated concentrations of this mineral can adversely affect some enzyme and electrolyte determinations. But inspectors often find that laboratories have not tested their source water for silicates or, if they've done so, the documentation has been misplaced.

The solution is simple: Laboratories need to test the source water—not the purifier effluent—for silicates. The NCCLS Guideline C3-A3 explains how to do this. Then, if high levels are found, the laboratory should install a water purification system capable of removing silicates.

The checklist does not require routine repeat testing for silicates. "But from a laboratory management standpoint, if you have a silicate problem in your source water and you're depending on your water system to remove that, it would make good sense to periodically check that it’s doing its job," Dr. Ruhlen suggests. It would also be a good idea for laboratories located in a geographic area with a silicate problem to repeat their testing if they have changes in their source water supply.