Ok, maybe this is a stretch, but here's an idea:
When he was younger, LA had that bad reaction to Accutaine involving platelet deficiency. It's apparently called
Thrombocytopenic Purpura (I found the name of the disease on Marinadedave's site.)
Thrombocytopenic Purpura can
apparently be treated with something called
Danazol (
wiki). Danazol is a modified testosterone. I wonder if the lab tests are sensitive enough to distinguish between Danazol and testosterone. Or, perhaps Danazol breaks down into testosterone with time & heat, or exposure to "cleaning fluid," chloroform, or ethanol. (Crap, if only I hadn't dropped organic chemistry... then maybe I'd know for sure
)
Anyway, maybe a syringe containing Danazol was still sitting in a medicine cabinet in the Ant's or LA's house, and KC (or, uh, the real killer) swiped it for other uses...
[Though, if the syringe came empty in a bag, this wouldn't make too much sense. And who knows if LA actually was prescribed Danazol injections. On the other hand, steroids (specifically methylprednisolone) are apparently a standard treatment for LA's disease. Methylprednisolone is structurally somewhat similar to testosterone, so maybe in the presence of heat/time/the-other-chemicals, it too could transform into testosterone, or something that would test as testosterone. Again, if only I'd gone through with that organic chem thing, perhaps I could say for sure. Heh.]