Further chemical tests are needed to prove that the substance is blood.
Presumptive testing has found widespread use by employers and public entities.
The FDA recommends for confirmatory testing to be conducted and the placing of a warning label on the presumptive drug test: "This assay provides only a preliminary result.
Clinical consideration and professional judgment should be applied to any drug of abuse test result, in evaluating a preliminary positive result.
To obtain a confirmed analytical result, a more specific alternate chemical method is needed.