I'm not very familiar with blood lab tests, but I believe many of them are some form of chromatography, e.g. HPLC, which is "just" a high-tech version of pee-on

I'm not very familiar with blood lab tests, but I believe many of them are some form of chromatography, e.g. HPLC, which is "just" a high-tech version of pee-on-a-stick tests. For those, there is a "control" indicator that should always show positive, and failure is when it doesn't show positive.