Cocaine, is it really there? Differing sensitivities of immunoassay drug screen and mass spectrometry

A case of a 23-month-old girl who presented with an upper respiratory tract infection and seizure activity potentially due to cocaine exposure has been described. Two urine samples were drawn 1.5hours apart. The initial sample was positive for the benzoylecgonine using an immunoassay screen and mass spectrometry-based tests. However, the sample drawn after about 1.5hours after the first one was negative for cocaine metabolite by immunoassay. The finding was consistent with the fact that the child had been exposed to cocaine with the low levels of metabolite suggesting either a low dose exposure or exposure that may have occurred a few days prior to her presentation. This case highlights the preanalytical variables such as timing of urine collection and its impact on urine drug testing.