Blind Standards

What are they?

A blind standard is a sample obtained from an external source, whose validated concentration is known to the facility supervisor, but is unknown to the lab analyst/technician. Unlike reference (PT) samples, blind standards do not have to be purchased from an approved provider. The only specification is that the samples obtained have a theoretical "true" value, and statistically determined acceptance criteria.

Also unlike reference samples, whose results are typically not received for some time after the testing is performed, the acceptance criteria are immediately available to the analyst. The exzception to this is those PT providers that offer a "rapid response" type of PT program. Blind standards can --and should--be used at any time there is concern about the control of a specific analysis. Having immediate access to the validated concentrations allows the analyst/technician to take immediate action to identify and correct the problem. These types of samples are important indicators of quality due to the real-time feedback on analytical performance obtained.

How often must they be analyzed?

Section NR 149.14(3)(j)specifies that blind standards must be analyzed three (3) times a year

if a standard is available
and
if the analyte was analyzed during the previous 4–month period.

Other Blind Standards Requirements

Analysis of blind standards must meet all of the following requirements:

• Analysis shall be conducted for each analyte in test categories 1 to 9, 15, and 19.
• Analysis shall be conducted for one analyte in each test category in test categories 10-14, 16, and 17.
• If the result for any analyte does not fall within the limits established by the provider or the laboratory, corrective action shall be taken by the laboratory and an additional blind standard shall be analyzed to verify that the corrective action was successful.
• The blind standard shall be analyzed at least 3 months and no longer than 5 months after the previous blind standard.