Today’s question comes from David:

“I am wondering what validation protocols you would recommend for your test strip products. Is it necessary to perform positive and negative controls every time a strip is used or is it assumed that if a batch of strips is in date and have been correctly stored then they will work directly from the shelf?”

-David

Thanks for the great question David. We love proactive customers who want to ensure they’re using our test strips correctly. We’re going to answer this question by first explaining the levels of quality control at our facility, and the stability of our test strips. We’ll arm you with enough information to make your own informed decision based on what might be best for your testing situation. Every situation is different, and thus, some may require more advanced checks of the strips, while others may not.

Quality Control

We routinely perform two types of tests for each batch of test paper made: precision of each concentration value and accuracy of the color chart. We check precision by testing multiple samples at one concentration value. For example, the 0-200 chlorine test papers are checked using a 5 ppm chlorine standard. This is the lower limit for this strip, so we are also verifying the detection limit. Ten randomly selected samples are tested. All ten samples must exhibit a positive reaction to the 5 ppm standard.

We also check accuracy for each batch. Accuracy is really a measure of the test strip performance with the color chart. We prepare standards at each of the color blocks on the label. These standards are verified using a secondary test method, usually a test kit. To pass, the test strips must test within +/- half a color chart unit at each concentration value. Continuing with the chlorine test paper example, with color blocks at 10, 50, 100, and 200ppm, a standard of 100 ppm chlorine would need to test somewhere between 75 and 150 ppm. Under normal conditions, the accuracy is often much better than +/- half a color chart unit, however, due to variations between users, lighting, paper, labels, and so on, the specification of +/- half a color chart unit is a practical one.

Stability

Our test strips are normally very stable, however, we do perform stability tests when we develop new products to determine how they should be stored. We vary the packaging to provide a suitable environment to maintain shelf-life. For example, if a particular test strip is susceptible to high humidity, we package it in a vial with a desiccant liner. If the test strip is susceptible to light, we package it in an opaque vial or an amber UV bag. In all cases, it is best to store our test strips in a cool, dry environment out of direct sunlight.

Validity

Under normal conditions, we don’t think that a check of each batch at your end is necessary. However, that really is up to you and should be determined based on the application. The more accurate the requirement, the more checks that may be necessary. Most strips are used in a semi-quantitative or qualitative fashion to economically monitor a situation and to compliment less frequently run, and more expensive, test methods (test kits, titrations, and meter methods). So, think about your specific situation and requirements, and knowing what you now know about our QC methods, do what you think is necessary.