I am begging people to
read the specs of the 5-panel EIA test. It
only detects
that the antibody binding sites are occupied,
not what they are occupied with. They will bind to either cocaine or cocaine metabolites, so if you only perform the antibody test on a sample of pure cocaine containing no metabolites you WILL get a strong positive. It says in the machine specs that they confirmed this to be the case while designing it, specifically by contaminating coke-negative hair with external contact.