Each batch is laboratory tested before shipped out. We find that most of the time the customers are not doing ketosis correctly. They may be losing weight because they cut out carbs, but they don't realize that fat intake needs to be around 75%+. And we understand some people are still learning about the keto process. Also please note that the strips are good 90 days after you open them.
Regardless, sometimes there could be a problem with the strips. We offer a lifetime guarantee.